Skin fit and retrofit: challenging the sustainability of curtainwall practice in tall buildings

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Skin fit and retrofit:
Challenging the sustainability of
curtainwall practice in tall buildings

Michael Robert Patterson

A Dissertation Presented to the
FACULTY OF THE SCHOOL OF ARCHITECTURE
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY IN ARCHITECTURE

December 2017

Copyright 2017 Michael Robert Patterson

ii
Dedication

To lifelong learning.

iii
Acknowledgements

My sincere gratitude to all who have extended such patience, encouragement and support
to me during this protracted academic pursuit; my remarkably talented Ph.D. colleagues
at the University of Southern California School of Architecture: Jeffrey Vaglio, Yara
Masri, Andrea Martinez, Lizzie Valmont, Eve Lin, Jae Yong Suk, Ed Losch, Simon Chiu,
and Myoboon Hur; my dissertation committee: Professors Douglas Noble, Marc Schiler,
Tridib Banerjee, and Karen Kensek; the School of Architecture administrative staff
including Lisa Shimabukuro, Jennifer Park and Jane Ilger; my business colleagues, and
the friends and family who have listened to the trials and tribulations of dissertation
trauma over too many years. A very special thanks to my esteemed friend and colleague
Professor Noble for his tireless efforts in support of us students and of the brilliant and
vitally important MBS and Ph.D. programs at the University of Southern California
School of Architecture. Thanks to my parents for patiently encouraging my education
until I could discover the joy of learning (it took awhile). And finally, my deepest love
and appreciation to my sweetheart Victoria; this was truly a collaborative effort realized
only with your unflagging confidence, patience, encouragement and support (we did it!).
Thanks to all!

iv
Table of Contents
Dedication ............................................................................................................................... ii
Acknowledgements ................................................................................................................ iii
Table of Contents ................................................................................................................... iv
Table of Figures ...................................................................................................................... x
Table of Tables ...................................................................................................................... xv
Abbreviations ....................................................................................................................... xvi
Chapter 1 — Skin deep in tall curtainwall buildings .............................................................. 1
1.1 Introduction .................................................................................................................... 1
1.2 Context ............................................................................................................................ 4
1.3 Summary ....................................................................................................................... 11
1.4 Chapter organization ................................................................................................... 12
Chapter 2 — Research description ......................................................................................... 18
2.1 Introduction to research approach ............................................................................... 18
2.3 Hypothesis .................................................................................................................... 22
2.4 Research goals and strategies ...................................................................................... 22
2.5 Research questions ....................................................................................................... 25
2.6 Research methods ......................................................................................................... 28
2.6.1 Descriptive research ................................................................................................. 28
2.6.2 Existing data sets ...................................................................................................... 28
2.6.3 facaderetrofit.org and surveys of building professionals ......................................... 28
2.6.4 Resilience Workshops .............................................................................................. 30
2.6.5 Case study research .................................................................................................. 32
2.7 Literature review .......................................................................................................... 32
2.8 Summary ....................................................................................................................... 37
Chapter 3 — Why skins: Building sustainability and the relevance of the façade zone .... 41
3.1 Building stresses: Why building-as-usual is a failure scenario ................................... 42
3.1.1 Building economic stresses ...................................................................................... 43
3.1.2 Building carbon stresses: Energy consumption and greenhouse gas (GHG)
emissions ............................................................................................................................... 43
3.1.3 Building social stresses: The challenge of urbanization, health and productivity ... 44
3.1.4 Building energy retrofits: The case for existing buildings ....................................... 44
3.2 Building types: Why tall? ............................................................................................. 46
3.2.1 Commercial Building Typology .............................................................................. 46
3.2.2 Tall Buildings ........................................................................................................... 48
3.3 The rise of the tall curtainwall building ....................................................................... 51

v
3.3.1 Skin and bones: A new building cladding technology for the post war building
boom 52
3.3.2 A Vertical Nexus ...................................................................................................... 55
3.3.3 Curtainwall technology ............................................................................................ 55
3.3.4 Unnatural ventilation ................................................................................................ 57
3.3.5 The aging modernist facade ..................................................................................... 58
3.3.6 It’s not all about glass .............................................................................................. 60
3.4 Sustainable skins .......................................................................................................... 60
3.4.1 Tall challenges and the lifecycle context ................................................................. 60
3.4.2 The measure of sustainability .................................................................................. 63
3.4.3 Is green building sustainable? .................................................................................. 66
3.4.4 The Dimensions of Sustainability ............................................................................ 69
3.4.5 Environmental Protection ........................................................................................ 71
3.4.6 Economic Development ........................................................................................... 71
3.4.7 Social Factors ........................................................................................................... 72
3.4.8 Sustainability and the building skin ......................................................................... 72
3.4.9 Façade functions and the façade affect zone ............................................................ 75
3.4.10 Operational energy in the façade zone ................................................................. 77
3.4.11 Sustainability is a Design Problem: Strategies to enhance façade performance . 78
3.5 The Strands of Façade Sustainability ........................................................................... 79
3.5.1 Façade Sustainability Attributes .............................................................................. 83
3.5.2 Construction and demolition C&D waste ................................................................ 86
3.5.3 Durability ................................................................................................................. 89
3.5.4 Economy .................................................................................................................. 92
3.5.5 Energy and carbon ................................................................................................... 93
3.5.6 Heritage value of TCBs ............................................................................................ 96
3.5.7 Indoor Environmental Quality ................................................................................. 98
3.5.8 Integration ................................................................................................................ 99
3.5.9 Resilience ............................................................................................................... 102
3.5.10 Water .................................................................................................................. 104
3.6 Summary ..................................................................................................................... 104
Chapter 4 — Skin deep durability: Extending service life and quality of curtainwall
systems to enhance sustainability of buildings and urban habitat ........................................ 105
4.1 Introduction ................................................................................................................ 105
4.2 Context ........................................................................................................................ 109
4.2.1 The time value of carbon ....................................................................................... 116
4.3 Dimensions of durability ............................................................................................ 117

vi
4.3.1 Why durability is important ................................................................................... 117
4.3.2 The expression of lifespan ..................................................................................... 118
4.3.3 Beyond operational energy: Embodied carbon ...................................................... 123
4.3.4 Supply chain considerations ................................................................................... 127
4.3.5 Differential durability: The compounded complexity of building assemblies ...... 127
4.3.6 Why buildings (and their façade systems) fail: Predicted versus actual service life
................................................................................................................................ 130
4.3.7 Linkage to Adaptability ......................................................................................... 136
4.3.8 Climate Change, Complexity, and Innovation ....................................................... 139
4.3.9 Maintenance: The M-word ..................................................................................... 140
4.3.10 Why buildings (and their facade systems) endure: All you need is love! ......... 144
4.3.11 Design Service Life Baselines for Buildings ..................................................... 145
4.3.12 Service Life Planning ........................................................................................ 153
4.4 Material matters: Durability and embodied carbon considerations .......................... 157
4.4.1 Low carbon material considerations ...................................................................... 158
4.4.2 Anchorage systems ................................................................................................ 159
4.4.3 Framing Systems .................................................................................................... 159
4.4.4 Infill Panel Materials .............................................................................................. 161
4.4.5 Finishes .................................................................................................................. 162
4.4.6 Architectural Glass ................................................................................................. 163
4.4.7 Differential durability and metal curtainwall assemblies ...................................... 165
4.4.8 Regenerative façade systems: Maintenance, repair and renovation considerations
................................................................................................................................ 175
4.4.9 More embodied impacts and durability considerations ......................................... 183
4.4.10 Lifecycle and the value of durability ................................................................. 188
4.4.11 Radical innovation ............................................................................................. 189
4.5 Guidelines to enhance façade system sustainability through considerations of
durability and embodied carbon ............................................................................................. 190
4.6 Summary, conclusions, and discussion ...................................................................... 197
Chapter 5 — Is glass green? Considering the Insulating Glass Unit ................................. 208
5.1 The problem with the IGU .......................................................................................... 209
5.2 High performance glazings ........................................................................................ 209
5.2.1 Unintended Consequences ..................................................................................... 210
5.2.2 Embodied Energy ................................................................................................... 210
5.2.3 Durability and Service Life .................................................................................... 210
5.2.4 Service Life Collapse and Wasted Durability ........................................................ 211
5.2.5 Recyclability .......................................................................................................... 211

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5.3 Design Goals and Assumptions for the m-IGU .......................................................... 212
5.3.1 Service Life ............................................................................................................ 212
5.3.2 Constraints ............................................................................................................. 212
5.5 Makeup of the m-IGU (Figure 7.1 and 7.2). .............................................................. 213
5.5.1 Material .................................................................................................................. 214
5.5.2 Glass ....................................................................................................................... 215
5.5.3 Films and Coatings ................................................................................................. 215
5.5.4 Durability Harmonization ...................................................................................... 216
5.5.5 New Tech Ready .................................................................................................... 216
5.5.6 Recycling the Chemical Soup ................................................................................ 216
5.5.7 Compression gaskets .............................................................................................. 216
5.5.8 Cassette frame ........................................................................................................ 217
5.5.9 Material .................................................................................................................. 217
5.5.10 Mechanisms ....................................................................................................... 217
5.5.11 Resilience Attribute ........................................................................................... 218
5.6 Vented Cavities in Façade Systems ............................................................................ 219
5.6.1 Consideration of a Vented IGU ............................................................................. 219
5.6.2 Gas Fills ................................................................................................................. 220
5.6.3 Cavity Ventilation Filter ........................................................................................ 220
5.7 Maintenance as a Strategy for Renewal ..................................................................... 221
5.7.1 Minimizing the Impact of Maintenance ................................................................. 221
5.7.2 Ease of maintenance: Access ................................................................................. 222
5.7.3 Frequency of maintenance ..................................................................................... 222
5.8 Integrated design and planning processes ................................................................. 223
5.9 Conclusion .................................................................................................................. 224
Chapter 6 — Supple Skins: A Methodology and Framework for Considering Façade
System Resilience ....................................................................................................................... 227
6.1 Introduction ................................................................................................................ 227
6.2 Bending Strength ........................................................................................................ 228
6.3 Resilience in the Public Sphere .................................................................................. 230
6.3.1 Resilience versus Sustainability ............................................................................. 235
6.4 The Larger Context .................................................................................................... 235
6.5 Resilience by Design ................................................................................................... 244
6.5.1 Resilience Thinking ............................................................................................... 246
6.5.2 Resilience at Scale ................................................................................................. 248
6.5.3 Design Objectives .................................................................................................. 250
6.6 Façade Links to Resilience ......................................................................................... 252

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6.7 The Subtleties of Resilience ........................................................................................ 253
6.7.1 Delivery Processes and Supply Chains .................................................................. 253
6.7.2 Durability ............................................................................................................... 254
6.7.3 Adaptability ............................................................................................................ 255
6.7.4 A Methodology for Evaluating Façade System Resilience ................................... 256
6.8 Principles of Façade Resilience ................................................................................. 258
6.9 A Framework for Building Façade Resilience ........................................................... 261
6.9.1 Resilience Factors .................................................................................................. 262
6.9.2 Metrics and Strategies for Façade Resilience ........................................................ 264
6.9.3 Ten Top Strategies to Enhance Façade Resilience ................................................ 265
6.9.4 Façade Resilience Table ......................................................................................... 268
6.10 Summary ..................................................................................................................... 271
Chapter 7 — Vintage skins: Retrofitting the tall face of Modernism ................................ 273
7.1 Introduction ................................................................................................................ 273
7.2 Context ........................................................................................................................ 275
7.3 Replacement versus rehabilitation ............................................................................. 280
7.3.1 A tale of two building types ................................................................................... 281
7.3.2 Vintage Midtown Manhattan tall curtainwall buildings ........................................ 283
7.3.3 Toronto’s multi-unit residential building towers ................................................... 285
7.3.4 Comparison of TCB and MURB Building Typologies ......................................... 287
7.3.5 Is the TCB a sustainable building typology? ......................................................... 288
7.4 Façade system renovation considerations of TCBs ................................................... 299
7.5 Façade retrofit types .................................................................................................. 305
7.5.1 Proposed TCB façade renovation typology ........................................................... 306
7.5.2 Renovation and restoration .................................................................................... 310
7.5.3 Refit and retrofit ..................................................................................................... 310
7.5.4 Selective enhancement and replacement (SER) ..................................................... 311
7.5.5 Overclad ................................................................................................................. 316
7.5.6 Reclad ..................................................................................................................... 326
7.5.7 Heritage building façade retrofits .......................................................................... 340
7.6 Reclad: The problem with façade system replacement .............................................. 349
7.6.1 High monetary cost ................................................................................................ 351
7.6.2 Disruption to ongoing building Operations ........................................................... 352
7.6.3 Hidden cost ............................................................................................................ 353
7.6.4 Motivational factors and selection of façade renovation type ............................... 354
7.7 Rethinking the building energy retrofit ...................................................................... 361
7.7.1 Façade-integrated deep green retrofits: Critical considerations ............................. 363

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7.7.2 Program objectives and goal setting ...................................................................... 364
7.7.3 Advances in curtainwall technology and retrofit practices .................................... 364
7.7.4 Beyond considerations of operational energy: Durability and adaptability ........... 372
7.7.5 Minimalist interventions: Reskin as a retrofit option of last resort ........................ 374
7.7.6 Cassette systems as an adaptive façade strategy .................................................... 374
7.7.7 The Veneer System for perpetual overclad ............................................................ 376
7.7.8 Incremental façade retrofits: Curtainwall technology as a strategy to step existing
buildings toward carbon neutrality ...................................................................................... 377
7.8 The preservationist’s perspective ............................................................................... 377
7.9 Renewable systems as a preservation strategy ........................................................... 383
7.9.1 Renewable systems: Maintenance as a restorative paradigm ................................ 384
7.10 Guidelines for TCB façade retrofit ............................................................................. 386
7.11 Summary and conclusions .......................................................................................... 388
7.11.2 A critical assessment of current retrofit practices .............................................. 394
Chapter 8 — Contribution, limitations, and future work ................................................... 395
8.1 Findings ...................................................................................................................... 397
8.2 Contributions .............................................................................................................. 405
8.3 Discussion and limitations ......................................................................................... 407
8.4 Future work ................................................................................................................ 410
8.5 Summary ..................................................................................................................... 413
Bibliography ............................................................................................................................... 415

x

Table of Figures
Figure 1.1: Iconic and landmark buildings like Lever House (left) and the Seagram Building, which share
the same intersection on Park Avenue in Manhattan, are easily identified as among the heritage of
Modernism. (Author’s photograph.) ___________________________________________________ 8
Figure 1.2: The character of urban habitat in areas like Midtown Manhattan is deeply influenced by the
early Modernist glass and metal curtainwall buildings. (Author’s photograph.) _________________ 9
Figure 2.1: A triangulation procedure was adopted as the strategy for testing the hypothesis in Section 2.2.
_______________________________________________________________________________ 39
Figure 3.1: Relationship and interactions of the “three pillars of sustainability,” ecological, economic and
social. (Source: Bell and Morse 2003) ________________________________________________ 42
Figure 3.2: From USGBC policy brief (USGBC 2011). _______________________________________ 67
Figure 3.3: The building façade is the nexus of many, often competing, considerations that ultimately
determine façade, and much of building, performance. ___________________________________ 73
Figure 3.4: Façade strategies and performance considerations as layered attributes toward the goal of
health, comfort and productivity. ____________________________________________________ 74
Figure 3.5: Energy end use data indicating areas typically affected by the performance of the building skin.
These areas are responsible for more than 50% of energy consumption (adapted from DOE 2012,
chapter 1-2). ____________________________________________________________________ 77
Figure 3.6: A sampling of design strategies and considerations in the façade zone (courtesy of Advanced
Technology Studio-Enclos). ________________________________________________________ 79
Figure 3.7: An interrelated and interdependent set of sustainability considerations developed for the
assessment of façade design and delivery practices in TCB applications. _____________________ 83
Figure 3.8: 5-year trend in monthly mean CO2 (NOAA 2017). __________________________________ 95
Figure 3.9: Concept for automating façade system integration (courtesy of Selkowitz, LBNL). _______ 101
Figure 4.1: Conceptual diagram of service life (adapted from Iselin and Lemer 1993, 16; Kesik 2002). _ 121
Figure 4.2: Area under curve equals durability, making component #2 the more durable. (Kesik 2002, 3)
______________________________________________________________________________ 123
Figure 4.3: Differential aging characteristics between components of an assembly may result in
replacement of the assembly and the premature service termination of the remaining fit components
(Kesik 2002) (graphic adapted from Kesik (2002). _____________________________________ 129
Figure 4.4: Conceptual diagram of link between maintenance and service life (adapted from Iselin and
Lemer 1993, 16; Kesik 2002). ______________________________________________________ 141
Figure 4.5: Cyclical renewals may extend service life by periodically elevating service quality (Iselin and
Lemur 1993, 22). ________________________________________________________________ 143

xi
Figure 4.6: Curtainwall anchored to column face. Anchor design accommodates adjustment in the x, y and
z directions (courtesy of Enclos). ___________________________________________________ 159
Figure 4.7: A 2-part silicone is applied between the fame and the IGU to bond the glass to the fame and
provide the weather seal. __________________________________________________________ 161
Figure 4.8: Section of shadow box at stack joint, with curtainwall anchor to building on right (courtesy of
Enclos). _______________________________________________________________________ 162
Figure 4.9: Typical insulating glass unit (IGU) construction. The wet sealant bonding of the space to the
glass to provide a hermetic seal, along with the coatings applied to the glass surfaces, reduce the
service life and compromise the recyclability of the glass material (Source: Advanced Technology
Studio – Enclos). ________________________________________________________________ 164
Figure 4.10: Javits Convention Center, New York City Pei Cobb Fried & Partners, 1986; FXFowle Epstein
renovation, 2014. During façade replacement: original curtainwall on left, new on right. _______ 165
Figure 4.11: Analysis of embodied energy use intensity of primary CW assemblies indicating how minority
materials—gaskets, seals, finishes—compromise service life of majority materials—aluminum,
glass—which represent the large majority of embodied GWP of the assemblies. ______________ 173
Figure 4.12: Curtainwall unit frames are factory assembled from fabricated aluminum extrusions and
gaskets fitted to extruded raceways (author’s photo). ____________________________________ 174
Figure 4.13: Typical horizontal stack joint between vertical curtainwall units showing location of primary
seal (Source: Advanced Technology Studio – Enclos). __________________________________ 177
Figure 4.14: Cyclical renewals may extend service life by periodically elevating service quality (adapted
from Iselin and Lemur 1993, 22; Kesik 2002). _________________________________________ 182
Figure 4.15: Procurement of curtainwall materials and assemblies for the LA Live Tower ( 2010, Los
Angeles, Gensler, façade contractor Enclos). __________________________________________ 185
Figure 5.1: Concept sketch for the m-IGU. ________________________________________________ 213
Figure 5.2: Concept sketch for the m-IGU. ________________________________________________ 214
Figure 5.3: The effects of IGU pillowing are apparent in the reflection of the building (left) in the glass
façade (right). __________________________________________________________________ 220
Figure 5.4: A conceptual semi-automated device to aid in the maintenance of the m-IGU by facilitating the
removal of the inner lite, or alternatively, the entire unit if required. (Advanced Technology Studio –
Enclos) ________________________________________________________________________ 223
Figure 6.1: Over efficiency can reduce redundancy and the ability of a system to adapt to stresses, causing
collapse and return to a state of less efficiency but greater resilience (adapted from Fisher 2013, loc
348). __________________________________________________________________________ 247
Figure 6.2: Organizational strategy for categorizing attributes, measures, and strategies of façade resilience.
______________________________________________________________________________ 257
Figure 6.3: The Resilience Strand is comprised of the primary attributes and considerations of façade
resilience. ______________________________________________________________________ 261

xii
Figure 7.1: The character of urban habitat in areas like Midtown Manhattan is deeply influenced by the
early Modernist glass and metal curtainwall buildings. (Author’s photograph.) _______________ 278
Figure 7.2: Iconic and landmark buildings like Lever House (left) and the Seagram Building, which share
the same intersection on Park Avenue in Manhattan, are easily identified as among the heritage of
Modernism. (Author’s photograph.) _________________________________________________ 278
Figure 7.3: Jane Exbury Towers. (Photo: Archives of Uno Prii.) ________________________________ 286
Figure 7.4: The cavity of the double-skin Shanghai Tower (2014, Gensler) encompasses extensive public
meeting and circulation space (author’s photo). ________________________________________ 295
Figure 7.5: Façade renovation typology (Adapted from Martinez et al. [2015]). ___________________ 307
Figure 7.6: Façade renovation type: selective enhancement. ___________________________________ 308
Figure 7.7: Façade renovation type: selective replacement. ____________________________________ 308
Figure 7.8: Façade renovation type: overclad. ______________________________________________ 309
Figure 7.9: Façade renovation type: reclad. ________________________________________________ 309
Figure 7.10: Façade renovation type: double-skin overclad. ___________________________________ 310
Figure 7.11: Original façade (author’s photo). ______________________________________________ 313
Figure 7.12: Horizontal band of operable windows were fixed shut (author’s photo). _______________ 314
Figure 7.13: Façade is inspected from suspended rig in upper right (courtesy of WASA). ____________ 314
Figure 7.14: Extensive water infiltration through the curtainwall had caused corrosion and rusting of
components (courtesy of WASA). __________________________________________________ 314
Figure 7.15: Original facade before overclad (Courtesy of MdeAS Architects). ____________________ 319
Figure 7.16: Installation of overclad curtainwall proceeding up left side of front elevation (Courtesy of
MdeAS Architects). ______________________________________________________________ 320
Figure 7.17: Roof area was used as staging for the many suspended work platforms (Courtesy of MdeAS
Architects). ____________________________________________________________________ 320
Figure 7.18: Installation of overclad curtainwall proceeding up left side of front elevation (Courtesy of
MdeAS Architects). ______________________________________________________________ 321
Figure 7.19: The completed overclad with a higher performing façade system presents a markedly different
building aesthetic (Courtesy of MdeAS Architects). ____________________________________ 321
Figure 7.20 Original masonry façade. ____________________________________________________ 323
Figure 7.21: Anchors have been installed in the pockets where the brick façade has been removed. The new
system being installed over the old to the right. (Photo courtesy of Alex Terzich) _____________ 324
Figure 7.22: Post-retrofit appearance is a radical departure from the original. (author’s photo) ________ 324
Figure 7.23: Javits Crystal Palace before reclad (author’s photo). _______________________________ 329
Figure 7.24: Original 5’x5’ grid with reflective glass (left), and new 5’x10’ module with higher visible light
transmission (right). (author’s photo) ________________________________________________ 330
Figure 7.25: A view to the east from inside reveals the difference in transparency between the new façade
system (left) and the original (right) (author’s photo). ___________________________________ 331

xiii
Figure 7.26: Another view under different lighting conditions of the new system (left) and the original
(right) (author’s photo). ___________________________________________________________ 331
Figure 7.27: Workers install the new curtainwall system and new entrances along east elevation (author’s
photo. _________________________________________________________________________ 333
Figure 7.28: Fixing detail of curtainwall system to steel spaceframe structure (author’s photo). _______ 333
Figure 7.29: A temporary roof structure allowed the convention center to remain operational throughout the
renovation process (author’s photo). _________________________________________________ 334
Figure 7.30: A mass of scaffolding sits atop the temporary roof structure (Figure 7.29) providing work
platforms and access to the skylight roof (author’s photo). _______________________________ 334
Figure 7.31: As the renovation of the convention center’s 15-story “Crystal Palace” nears completion, the
increased light transmission of the façade system is evident (author’s photo). ________________ 335
Figure 7.32: Original façade elevation. (photo courtesy Filip Maljković) _________________________ 336
Figure 7.33: Renderings compare the added vision glass area in the original façade (above) with the new
scheme (below) (courtesy of Pei Cobb Freed & Partners). ________________________________ 337
Figure 7.34: Section of original stick curtainwall above with new unitized reclad scheme below (courtesy
of Pei Cobb Freed & Partners). _____________________________________________________ 337
Figure 7.35: Rendering including planned unitized reclad façade system. ________________________ 338
Figure 7.36: Rendering of new unitized reclad system, reflecting use of same overall grid and emphasized
verticality as the original façade design (courtesy of Pei Cobb Freed & Partners). _____________ 338
Figure 7.37: The progression from left to right reveals the reduction in spandrel area and increase vision
glass module (courtesy of Pei Cobb Freed & Partners). __________________________________ 338
Figure 7.38: Original façade system, west elevation, circa. 2007. Note the reflectivity. (photo credit I,
Padraic Ryan). __________________________________________________________________ 341
Figure 7.39: West elevation in process façade installation; old system below mechanical floor grills, new
system above. Reflectivity of old façade caused by application of a solar film. The new façade is
intended to restore the original glazing tint (authors photo). ______________________________ 343
Figure 7.40: Suspended scaffolding rig provides work area for demolition of old and installation of new
curtainwall systems (author’s photo). ________________________________________________ 344
Figure 7.41: Detail of temporary outrigger structure to suspend scaffolding rig (author’s photo). ______ 344
Figure 7.42: Construction lift on east elevation used to move old materials out and new materials in
(author’s photo). ________________________________________________________________ 345
Figure 7.43: View of completed east elevation from the East River on an overcast day (author’s photo). 346
Figure 7.44: Scope items reported from the original surveys indicate the potential for change to building
appearance. ____________________________________________________________________ 350
Figure 7.45: Survey response to goals as a component of façade renovation program (Martinez et al.
2015a). ________________________________________________________________________ 356
Figure 7.46: Survey response to design and analysis strategies included in façade renovation program
(Martinez et al. 2015a). ___________________________________________________________ 356

xiv
Figure 7.47: Insulating glass unit (IGU) surfaces and components. ______________________________ 366
Figure 7.48: Rendering of a double-skin façade concept with a laminated glass outboard skin and an IGU
inboard skin. The cavity provides protection for an automated dynamic shading system (courtesy of
Enclos). _______________________________________________________________________ 369
Figure 7.49: Section detail of vertical mullion; concept for a removable cassette glazing system (image
courtesy of Advanced Technology Studio–Enclos). _____________________________________ 375
Figure 7.50: Insulated glass units are generally combined with body tints, low emissivity (low-e) and
spectrally selective surface coatings, ceramic frits, warm-edge spacers and gas fills to further enhance
performance; all process that yield noticeable differences in the visual and optical properties of their
products. ______________________________________________________________________ 380
Figure 7.51: The façade renovation of the Javits Convention Center involved design changes including an
alteration of the glazing grid from 5x5 to 5x10 foot (left; old curtainwall system on left and
replacement on right) (author’s photo). _______________________________________________ 382
Figure 7.52: Another material change on the Javits renovation was a stainless-steel panel system to replace
spandrel glass along the south wall (author’s photo). ____________________________________ 382
Figure 7.53: Renewable façade systems last until the decision is made to terminate their service
independent of considerations of visual and performative quality, those key attributes being cyclically
maintained within specified boundaries (adapted from Kesik {2002}). ______________________ 385

xv
Table of Tables
Table 3.1: Façade functions and performance contributions ......................................................................... 76
Table 3.2: Proposed planetary boundaries. Derived from Rockström et al. (2009, 8-9) and Folke (2013, 22-
24). ........................................................................................................................................................ 81
Table 3.3: Primary and secondary façade zone sustainability attributes must be integrated in balanced
response as part of holistic building design process, considered over building lifecycle. ................... 85
Table 4.1: Categories of threat to service life (from Silva et al. 2016, 16). ................................................. 132
Table 4.2: Factors in determining design service life (Athena Institute 2006, 9-16; Straube and Burnett
2005, 37-42; ISO 2000). ..................................................................................................................... 148
Table 4.3: Summary of service life and design service life data and opinion from literature review. ........ 150
Table 4.4: Baseline material analysis of CW system (Source: James Casper). ........................................... 171
Table 4.5: Embodied energy approximation of baseline CW system using ICE LCI data (Hammond and
Jones 2011), with predicted service life averages. ............................................................................. 172
Table 4.6: Attributes of low carbon assemblies. .......................................................................................... 184
Table 5.1: Preliminary embodied energy analysis for baseline IGU. Embodied energy values from ICE
database (Hammond and Jones 2011). ............................................................................................... 215
Table 6.1: The following principles of façade resilience are a product of this research derived from
workshops, surveys, and literature review as described in Section 2.5.4, and partially derived from the
work of the Resilient Design Institute (2012-2013a). ........................................................................ 258
Table 6.2: Twelve factors have been identified as the primary attributes of façade resilience. .................. 262
Table 6.3: This collection of resilient façade design strategies is in part derived from the Principles of
Façade Resilience in Table 6.1, and both are a product of this research derived from workshops,
surveys, and literature review as described in section 2.5.4. ............................................................. 265
Table 6.4: Table of façade resilience factors, metrics, and strategies. ......................................................... 269
Table 7.1: Manhattan buildings data disclosure (NYC 2017). .................................................................... 283
Table 7.2: A summary of pros and cons of the tall building type (derived from Sturgis 2017a; Smith 2016;
Ijeh 2015). .......................................................................................................................................... 290
Table 7.3: Summary of case study data in Section 7.5. (cost in USD). ....................................................... 347
Table 7.4: Ownership and occupancy from EIA (2012) Table C3 .............................................................. 359
Table 7.5: Sustainability objectives for façade retrofit applications on TCBs. ........................................... 364
Table 8.1: Summary findings. ...................................................................................................................... 397
Table 8.2: Table of contributions to the field of tall curtainwall building façade technology. ................... 406

xvi

Abbreviations
AGGI – Annual greenhouse gas index
AIA – American Institute of Architects
APT – Association of Preservation Technology
ASR – Automobile shredder residue
ASTM – American Society for Testing and Materials
BIPV – Building-integrated photovoltaics
BMS – Building management system
BOD – Basis of design
CBECS – Commercial Buildings Energy Consumption Survey
CNR – Carbon-neutral ready
CSA – Canadian Standards Association
CTBUH – Council on Tall Buildings and Urban Habitat
CW – Curtainwall
DER – Deep energy retrofit
DOE – Department of Energy
EIA – Energy Information Administration
EISA – Energy Independence and Security Act
EPD – Environmental product declaration
EUI – Energy use intensity
FAR – Floor area ratio
FSLP – Façade service life planning
GHG – Greenhouse gas
GSA – General Serviced Administration
FEMA – Federal Emergency Management Administration
HVAC – Heating, ventilation and air conditioning
IBC – International Building Code
IBHS – Insurance Institute for Business & Home Safety
ICE – Inventory of Carbon & Energy
IEQ – Indoor environmental quality
ISO – International Standards Organization
LCA – Lifecycle assessment

xvii
LCCA – Lifecycle costing analysis
LCI – Lifecycle inventory
LEED – Leadership in Environmental and Energy Design
MSW – Municipal solid waste
NBI – National Building Institute
NIBS – National Institute of Building Science
NOAA – National Oceanic and Atmospheric Administration
OPR – Owner’s project requirements
PNNL – Pacific Northwest National Laboratory
PV - Photovoltaics
SER – Selective enhancement and replacement
SES – Socio-economic system
SLP – Service life planning
TCB – Tall curtainwall building
UNEP - United Nations Environment Programme
USGBC – United States Green Building Council
WBDG – Whole building design guide
WWR – Window-to-wall ratio
ZNE – Zero-net energy

1

Chapter 1 — Skin deep in tall curtainwall buildings
1.1 Introduction
The global warming effects of climate change resulting from greenhouse gas (GHG)
emissions—produced or accelerated through the industrialization of human societies and
primarily involving the burning of fossil fuels—are increasingly recognized as an
escalating threat to human and other species (Gore and Gellert 1994; Santer, Wigley,
Barnett and Anyamba 1996; Parmesan and Yohe 2003; Schwartz and Randall 2003;
Oreskes 2004; Hansen, Sato, Ruedy et. al. 2006; Rosenzweig, Karoly, Vicarelli et. al.
2008; IPCC 2014). This has brought increasing attention to the patterns of energy
consumption and sustainable development in society. There is now widespread
recognition in the sciences that the building sector is a significant part of the problem
(AIA 2017; Architecture 2030 2017; EISA 2007). In developed countries, the building
sector is a leading consumer of energy and producer of carbon emissions. Using U.S.
Energy Information Administration data (EIA 2012) Architecture 2030 (2017) has
calculated that buildings are responsible for 47.6 percent of energy consumption, nearly
as much as the industrial and transportation sectors combined. In addition, U.S. buildings
consumed three-quarters of electricity and generated nearly half of all carbon emissions.
While critical considerations of sustainability extend throughout all sectors of the global
economy, buildings and the built environment have been revealed as the leading impact
sector.
Climate change effects and escalating environmental impacts resulting from resource
utilization have brought increasing urgency to building energy performance and related

2
greenhouse gas emissions—the dominant focus on energy consumed during the
operational phase of buildings—but also a growing realization of the role of embodied
energy in a building’s eco footprint (La Roche 2017). The pursuit of net-zero
energy/carbon performance in commercial and large multifamily residential buildings is
imperative (Pless and Torcellini 2009, 18; Aksamija 2015; La Roche 2017). Existing
buildings are the biggest contributor to the problem, and the façade plays a pivotal role in
achieving building energy efficiency goals (Olgyay and Seruto 2010; Killien 2011; Hart
et al. 2013). Plans for reducing carbon emissions such as New York City’s 80 x 50 plan
to reduce greenhouse gas emissions by 80 percent over 2005 levels by 2050 cannot be
attained through more efficient new construction alone (NYC 2014). Existing building
enclosures will have to be retrofitted, and in particular those that are known to have high
energy consumption and poor thermal performance.
According to U.S. Energy Information Administration statistics, building renovation has
historically approximately equaled new construction, or about 5 billion square feet
annually (Mazria and Kershner 2007, 10). Should this trend continue, Architecture 2030
projects that some three quarters of the building stock will be comprised of either new or
renovated buildings by the year 2035. This represents a tremendous opportunity to
fundamentally transform the commercial building sector in the relatively near future, with
renovation of the existing building stock as a critical component. Building renovations,
however, take many forms and are undertaken with varying motivations. Some
renovations may not improve a building’s patterns of energy consumption at all; some
may even make it worse. A new form of building renovation has emerged as part of the
green movement in the building industry, what is commonly referred to as a building
energy retrofit, with the objective of improving energy performance. Most often,
however, these retrofits involve the replacement of mechanical and lighting systems and
fail to address the façade system, which significantly limits the effectiveness of the
retrofit in optimizing energy efficiency (Olgyay and Seruto 2010; Killien 2011; Hart et al.
2013). Deep energy renovations (DER) have as their benchmark energy consumption
reductions of 50 percent or more, but increase the cost and complexity of the renovation
work . Adoption of optimized retrofit practices represented by DERs has been slow, for
reasons first articulated by Lovins (1992) but still valid today:
§ Absence of consideration of building system interactions and the requirement for
systems integration in whole-building design.

3
§ First cost and simple payback cost analysis rather than lifecycle costing analysis
(LCCA).
§ Financing is problematic for many building owners and does not encourage
integrated whole-building renovations.
§ The split incentive problem in which the owner incurs a disincentive in pursuing
energy efficiency.
Killien (2011) and Hart et al. (2013) also note a lack of knowledge among practitioners
regarding the why and how of DER implementation.
Energy is not the only consideration when considering the sustainability and resilience of
existing buildings and the opportunity and challenges presented by their renovation.
Climate is a dominant consideration in shaping building design. A change in climate will
alter design practices and reshape the interaction between building and environment, and
a building’s exposure to predicted climate change impacts should even be considered in
the assessment of renovation value (Gething 2014, 36, 42). Hotter summer temperatures,
for example, increase the probability of overheating, at least in the perimeter zones,
bringing increased advantage in solar shading strategies. Climate change is accelerating,
bringing uncertainty to future climatic conditions (Stainforth et al. 2005, 403; Climate-
ADAPT n.d.). Buildings are long lived artifacts of the built environment, and will likely
experience increased climate variation over their service lives. The ability of buildings to
readily adapt to these changing conditions will play a large role in determining the
resilience of buildings and urban habitat. The façade system presents an opportunity to
build adaptive capacity into a building. Curtainwall systems service life is typically less
than that of the building (Section 4.3.11). While this is not current practice, the
curtainwall system affords the opportunity to plan for cyclical façade retrofits, where
such factors as façade condition and climate changes can be assessed and the façade
system tuned to balance thermal and solar behavior, and other appropriate adaptations
can be made in response. If future conditions produced by climate change effects are
unpredictable now, then at least the need for adaptability in buildings and their major
systems can be anticipated, and steps taken in façade system design to facilitate such
things as inspection and replacement of the weather seals, retrofit of glass panels, options
for adding insulation, and the attachment of exterior solar shading devices.

4
The challenges presented by the façade retrofit of existing buildings point to more
fundamental problems in façade system design that will ultimately impact buildings
under construction today. Within an approximate 30 to 40-year time frame of new
building construction, multiple motivations will likely emerge for façade retrofit:
§ deterioration in the appearance of façade materials,
§ a decline in product performance attributes,
§ the availability of new, higher performing products and materials,
§ a desire to change or upgrade a building’s image,
§ the recognition that exterior shading is an optimal response to climate change.
The challenges are caused by the complete failure of the building industry to anticipate
and accommodate this easily identifiable future requirement of adaptability.
The building sector is comprised of many building types. The Energy Services
Administration (EIA) categorizes 14 principal building types in the commercial sector by
activity (CBECS 2015). Renovation practices for buildings and their major systems must
be tuned to the nuances of building type (Jerome and Ayon 2014). One distinct building
type not categorized by activity as in the EIA scheme is the tall building, the purview of
the Council on Tall Buildings and Urban Habitat (CTBUH 2017a). Tall buildings house a
broad range of activities, from residential to office. De Jonge (1006, 8) comments that tall
buildings are strongly linked with curtainwall façade systems. This linkage forms a
distinct and dominant subcategory of tall buildings, the tall curtainwall building (TCB).
(Note: referenced Section numbers, e.g., Section X.X.X, refer to numbered sections in
this document.)
1.2 Context
The TCB typology of the twentieth century is an icon of Modernism. Architects
producing these icons included Mies van der Rohe, Le Corbusier, Oscar Niemeyer,
Minoru Yamasaki, I.M. Pei, Gordon Bunshaft, and many others. The better-known icons
include the UN Secretariat Building (Le Corbusier, Oscar Neimar, Wallace Harrison et
al., 1952), Lever House (Gordon Bushaft and SOM, 1952) and the Seagram Building
(Mies van der Rohe, 1956-58) in New York City, the National Congress of Brazil in

5
Brasilia (Oscar Niemeyer, 1957-64), and again, many others. These early icons inspired a
new vernacular of tall curtainwall buildings (TCBs) of a notably lesser quality
(Wigginton 1996, 96).
Lost amidst the current unprecedented global boom in tall building construction is that
the earliest of this building type dating back to the mid twentieth century are now fifty
years of age and more, in service far longer than their builders anticipated (Browning
2013). Some few have undergone major renovation. The large majority have not, and
represent a looming need for renovation on an urban scale. A defining characteristic of
these Modernist glass towers that so quickly redefined the skylines of major urban areas
in the U.S. and Europe is the modular metal and glass curtainwall, combining both the
face and enclosure of these buildings, defining both building skin and urban habitat. As
these buildings have aged and become the focus of rehabilitation considerations, this
façade system typology has proven to be a significant renovation challenge (Henket
1996, 14).
Both the need and the complexity of curtainwall retrofit on vintage TCBs is amplified by
the dramatic change in performance expectations since their construction. Energy
conservation, thermal and acoustical performance, solar control, daylighting, and
ventilation requirements have evolved well beyond initial parameters. In addition, the
conditions of use have changed. Urban environments have grown increasingly dense,
along with noise, light and air pollution. As it turns out, curtainwall system designs have
proven very poorly equipped to adapt to these changes (Section 4.3).
Many of these buildings were constructed during the post-war building boom in the mid
twentieth century, a period of cheap energy prices characterized by little consideration for
energy performance, and a time when building science was poorly understood and
seldom applied. It was also a period of experimentation with emergent and unfamiliar
systems and materials (Wigginton 1996, 3.94-3.96; Ayón and Rappaport 2014, 18).
These factors, combined with a construction ethic that anticipated building lifespans as
limited to a maximum of 30 years, resulted in buildings of poor quality and limited
durability, buildings that were poor performers from the beginning and that have not aged
well. These buildings are now 40 to 50 years old and more and comprise a significant
percentage of the commercial building sector in urban zones like Midtown Manhattan
(Rappaport and Sigge 2004). The sheer quantity of these buildings renders it impractical

6
to consider their demolition and reconstruction as a standard practice. Rather, it is
imperative that efficient methods are developed to significantly prolong the lifespan of
these buildings. Consequently, goals for future reductions in energy consumption and
related carbon emissions must be built on a foundation of improvements to the existing
building stock (Elefante 2007).
The opportunity is significant. Richards (2015) describes the rejuvenation of tired
buildings as the “realignment of a building’s durability with long-term economic value.”
Tishman Construction, one of the largest general contracting firms operating in New
York City, has a “building repositioning” team specializing in existing building
renovations. The team’s director notes, “There are 440 million square feet of commercial
space in New York City. Of that, about 70 percent was built before 1980. The current and
future market is in transforming these buildings to be energy efficient, sustainable,
marketable, and updated” (Hauserman 2016). Unfortunately, TCBs are proving
particularly challenging whole-building renovation candidates.
Curtainwall technology and its application developed rapidly in the mid twentieth
century. These new lightweight cladding systems gained swift market adoption as an
alternative to the masonry infill wall practices of the time. Combined with the use of
passenger elevators and air conditioning systems, this new technology owed its initial
success to the embrace of the real estate development community, which recognized the
benefit in the increased leasable floor area provided by the thin cladding systems
(Wigginton 1996, 96). Multiplied by each floor, this advantage was significant, and
served as one important aspect in the emergence of the tall building form.
Built principally for office buildings in the days of cheap and abundant energy, energy
efficiency and comfort were not predominant concerns of TCB design and construction.
They were also realized amidst an emerging throwaway culture in which the lifespan of
even a tall building was regarded as perhaps 20 years (Browning 2013), eliminating
considerations of durability and service life as design drivers. Despite the advancing age
of these early applications, relatively few have undergone façade interventions of any
significance (Patterson and Vaglio 2011a). There are good reasons for this; it turns out
that the tall curtainwall building presents a challenge when it comes to the renovation of
these exterior wall systems. Cost and, even more, disruption to ongoing building
operations, act as significant barriers to façade interventions in this building type. Even

7
the relatively recent trend of building energy retrofits that has found traction in the
commercial building sector frequently stops short of addressing holistically the
unprecedented challenge of retrofitting the curtainwall. In many instances, the low-
hanging fruit of HVAC and lighting systems are upgraded while the aged, substandard
façade systems are left intact (Olgyay and Seruto 2010; Hart et al. 2013). With this
limited approach, the opportunity for optimizing energy performance and comfort
through the integration of the major building systems is lost, with the very real prospect
that the façade system will soon require major repair or replacement in any case. Deep
energy retrofitting necessitates consideration of the building envelope (Killien 2011; Hart
et al. 2013) and in the case of older TCBs, it generally requires a significant level of
intervention with the facade system.
There is also emerging recognition of the potential heritage value of the TCB building
type (Ayón and Rappaport 2014). Appreciation for the “glass box” tall curtainwall
building as an expression of Modernism has waxed and waned since the time of its
widespread appearance in the 1960s, and opinions vary widely among owners,
professionals, the public and academics alike as to its cultural value. Some of the older
curtainwall buildings are clearly an important part of the heritage of Modernism and
deserving of preservation. Iconic and landmark buildings like Lever House and the
Seagram Building are easily singled out in this respect (Figure 1.1).

8

Figure 1.1: Iconic and landmark buildings like Lever House (left) and the Seagram Building, which
share the same intersection on Park Avenue in Manhattan, are easily identified as among the
heritage of Modernism. (Author’s photograph.)
Less significant manifestations of this architectural style are abundant and in need of
façade renovation. These buildings are integral to the texture of urban habitat and their
contextual contributions and character-defining presence has been thoroughly
documented in commercial areas such as Midtown Manhattan (Figure 1.2), where more
than two hundred modern curtainwall buildings were recorded in a survey performed by
the local Docomomo chapter (Rappaport and Sigge 2004, 113). There is a growing
awareness of the vernacular value of these buildings, and calls for increased protections
including landmark designations continue to arise (Jerome 2014). The recent designation
as a New York City Landmark of the Citicorp Center at 601 Lexington Avenue (Hugh A.
Stubbins, Jr., Emery Roth & Sons, and E.L. Barnes, 1974-78), however, is an interesting
development in the saga of the rezoning of Midtown Manhattan. As landmark petitions
for other Modern buildings in the area languish, this designation reinforces the notion that
only the high-profile examples of this building type will be preserved and that many tall
vernacular TCBs will likely remain unprotected and subject to significant alterations for
years to come.

9
In the United States, some relevant
discussions have started to take place
within the framework of preservation
scholarship, advocacy and research. A
roundtable discussion on the rehabilitation
of curtainwalls organized by Docomomo
NY/Tri-State in 2013 brought together
several practitioners in the subject to
discuss some of the more relevant
challenges (Ayón and Rappaport 2014). A
symposium—Renewing Modernism –
Emerging Principles for Practice—
organized by the APT’s Technical
Committee on Modern Heritage and
Technical Committee on Sustainable
Preservation and conducted during the APT
2015 annual conference in Kansas City
catalyzed important discussion on the
renovation of Modern glazed facades, as
well as emerging principles and best
practices for intervention.
Complicating considerations of cultural
significance and heritage value are multiple factors (discussed in section 7.3), but an
overarching consideration is the environmental impact of the building sector. Climate
change effects have brought increasing urgency to building energy consumption and
resulting greenhouse gas emissions, and produced a growing realization of both the
operational and embodied impacts comprising a building’s eco footprint. The push is on
for net-zero (Peterson, Torcellini and Grant 2015; NBI 2017) or net-zero-ready (DOE
n.d.) performance in commercial and large multifamily residential buildings, with respect
to an expanding array of impacts including energy, carbon, water and waste. Existing
building enclosures must ultimately be retrofitted, especially the many that are known to
have high energy consumption and poor thermal performance, as with the vintage TCB
stock. Assessment of heritage value and the development of preservation strategy for any
given building must be undertaken in support of appropriate resilience and sustainability

Figure 1.2: The character of urban habitat in
areas like Midtown Manhattan is deeply
influenced by the early Modernist glass and
metal curtainwall buildings. (Author’s
photograph.)

10
goals at the local, regional, and national scales. The preservation of buildings and urban
habitat is an important component of the sustainability dialogue, but it is one among
many that must be balanced against each other to achieve successful outcomes.
The focus on operational energy consumption has masked other important considerations
vital to the realization of sustainability; embodied impacts, health and productivity,
resilience, durability and adaptability among them. While energy is the dominant issue,
and the most studied, other factors must also be considered in developing sustainable
solutions to the problems of global consumption. Sustainability issues are complex,
multivariate whole-systems problems that must be addressed holistically to arrive at truly
sustainable solutions.
Buildings and their façade systems are complex, layered assemblies developed in
response to varied, and often competing, demands. Buildings, through their enclosures,
must provide for the safety, security, and privacy of the occupants, along with protection
from the elements, while simultaneously providing connection, visually and physically,
to the exterior (Allen 1995). The provision of sensorial comfort in the form of visual,
thermal, acoustical and biophilic attributes of the interior environment, especially as it is
linked to human health and productivity, have relatively recently become a predominant
focus of building performance (WELL 2017). Buildings are further expected to provide
these functions at a competitive cost, with minimal environmental impacts, and with
minimal maintenance over an extended period of time. At this level of functionality, there
is little to differentiate the façade system from the building itself. Straube and Burnett
(2005, 40) bring the building science perspective and a greater level of detail to building
enclosure considerations with a list of physical functions and qualitative attributes that
each building must strive to satisfy, with all but the first and last two being attributes of
in-service performance, and all directly applicable to the façade system:
§ constructability
§ economic viability (short and long-term cost)
§ viewability (appearance: aesthetic, cultural, stylistic)
§ utility
§ sustainability
§ serviceability

11
§ safety: life, health, injury, property, enterprise
§ productivity
§ operability
§ maintainability
§ repairability
§ durability
§ adaptability
§ disposability
These various considerations converge in the façade system and must be accounted for in
curtainwall system design and delivery, but they are poorly understood and often ignored.
1.3 Summary
Climate change brings urgency to carbon reduction from the built environment, buildings
being the leading carbon producing sector. Deep energy renovations of existing buildings
integrating façade system retrofits is potentially the most effective strategy to bring
transformation to building sector performance. Old TCBs dating back to the mid-
twentieth century are notable for their poor thermal and acoustical performance and
substandard in the control of air and water penetration and the provision of comfort.
Designed for no explicit service life duration, the original curtainwall systems are
approaching 50 years of service and more, and need refurbishment. Their design provides
few options for renovation, with those providing upgrades to contemporary façade
performance standards being costly and disruptive to building users and ongoing building
operations. Complicating these issues is the growing recognition of the cultural value of
these artifacts of twentieth century Modernism. The highly-glazed curtainwall is
commonly singled out as a contributing factor to poor building energy performance. At
the same time, it provides the benefits of daylight and connection to the outdoor
environment, and occasionally ventilation. The façade system is uniquely positioned at
the nexus of many competing variables that must be carefully considered and balanced on
a case-by-case basis in TCB façade system design.

12
1.4 Chapter organization
This document is comprised of 8 chapters, the basic content of each briefly described
following.
Chapter 1: Skin deep in tall curtainwall buildings
Tall curtainwall buildings (TCBs) are a discrete building type with
historical, cultural and technological roots in twentieth century Modernism
as an experimental building form. They are a component of the opportunity
present in the upgrading of the existing building stock, but also present
unique performance and retrofit challenges linked to the attributes of the
TCB typology.
Chapter 2: Research description
The sustainability of contemporary curtainwall practices is challenged with
two key arguments: 1—contemporary metal curtainwall systems fail to
support service life duration and quality consistent with sustainable building
performance, and 2—enhancing curtainwall system durability can extend
service life and quality, thereby amortizing embodied carbon over a longer
period and resulting in a reduction in environmental impacts, with
consequent contributions to the sustainability of the building sector. The
tested hypothesis was:
The service life of metal curtainwall systems can be extended through a
renewal strategy of planned maintenance, retrofit and renovation
cycles, that perpetuates service life, thereby providing advantages that
improve building sustainability as compared with a cyclic system
replacement strategy.
Considerations of durability, adaptability, embodied carbon, resilience and
heritage value provide gateways to a deeper assessment of TCBs and their
façade systems, and curtainwall design, delivery and renovation practices.
Surveys, interviews and workshops with industry practitioners reveal the
predominance of reclad as a façade renovation strategy. Case studies are
useful in developing a façade renovation typology and in revealing the

13
underlying problems that render TCB renovation a challenge. Literature
across disciplines of building science, social science, facilities management,
industrial ecology, engineering and construction, and historic preservation
addresses considerations of sustainability, resilience, service life prediction,
obsolescence, durability planning, lifecycle assessment, construction and
demolition waste, renovation and retrofit, building materials and
maintenance.
Chapter 3: Why skins? Building sustainability and the relevance of the façade zone
The origins and historical development of tall buildings and curtainwall
systems provides necessary context for understanding their relevance among
the existing building stock, and the opportunity of facade-integrated
building retrofits in TCBs. The development of sustainability criteria
relevant to the building skin includes energy and carbon, durability,
adaptability, resilience and heritage value. The application of these criteria
to TCB façade design, delivery, repair, maintenance, retrofit, renovation and
end-of-life processes reveals shortcomings worthy of further inquiry.
Chapter 4: Skin deep durability: Extending service life and quality of curtainwall
systems to enhance sustainability of buildings and urban habitat
Durability provides a rich line of inquiry that exposes significant
shortcomings in curtainwall practices in supporting sustainable outcomes.
Curtainwall systems are comprised of high-intensity materials,
approximately 88 percent glass and aluminum, both with long service life
potential, but weak links in the assemblies of weather seals and finishes
collapse actual service life to 35-50 years. Curtainwall systems are found to
be poorly designed for repair, maintenance, retrofitting and renovation
purposes, all strategies that could potentially be used in service life planning
to extend service life and reduce lifecycle embodied carbon by as much as
50 percent. In addition, new unitized systems may prove to be less durable
and adaptable than their early progenitors. Alternatives to standard practices
are required to promote sustainable outcomes. Guidelines for durable
building-integrated façade development that minimize lifecycle carbon
consider the integration of alternative pre-design, planning, system design,

14
procurement and instillation, emphasizing material selection and service life
planning.
Chapter 5: Is glass green? Considering the Insulating Glass Unit
The insulating glass unit (IGU) is identified in chapter 5 as a weak link in
the curtainwall system, with a predicted service life of only 20-25 years.
Abandoning convention and rethinking strategies for adding insulation value
to the vision-glass area of the façade system with the goal of significant
service life extension, and the adopted constraints of reuse and recyclability
for all system materials and components, necessitates the dis-integration of
the IGU into an unbonded assembly with layered functionality, avoiding, for
example, laminations and glass coatings that could potentially compromise
recyclability. The resulting concept for a disassemblable IGU relies on
maintenance and service life planning to extend service life indefinitely,
potentially optimizing the service life of glass. Limiting the recurring
embodied carbon impact of maintenance would require a future
developmental focus on minimizing required maintenance and optimizing
its efficiency. The conceptual exercise tests the notion that constraints can
drive radical solutions that may not be converged on through a series of
incremental improvements—the current trajectory of IGU development. In
the process, limitations are revealed in current insulating glass assemblies.
The exercise demonstrates the potential for the development of viable
alternative products.
Chapter 6: Supple Skins: A Methodology and Framework for Considering Façade
System Resilience
Resilience and sustainability are linked concepts; considerations of
resilience have been elevated by the emerging shocks and stresses driven by
global climate change. Resilience is a whole-system concept that has been
reinterpreted and developed by a range of scientific disciplines, but perhaps
most usefully in a vein of socio-ecology that provides another unique and
informative lens through which to view the behavior of TCBs and their
façade systems. Considerations of resilience provide a different base from
with to consider curtainwall practices, one where the pursuit of efficiency
must be balanced against the redundancy necessary to enhance system

15
resilience. Earthquakes, floods, fires, and extreme wind and temperatures
link the façade to resilience. Findings reinforce the relevance of durability
and adaptability concepts and their application to the evaluation of TCB
curtainwall practices as developed in chapter 5. Resilient façade system
designs anticipate future uncertainty, embrace geometric simplicity and
avoid high levels of customization, all of which run counter to current trends
in façade system design.
Chapter 7: Vintage skins: Retrofitting the tall face of Modernism
“The greenest building is the existing building” is an often-repeated
aphorism; building reuse is a fundamentally sustainable action. Some
buildings are more easily reused that others, and the same is true of building
types, as evidenced by a comparison of the TCB with the multi-unit
residential building (MURB) type. Inherent design flaws in many TCBs
include an under-designed structural system and deep floor plates combined
with shallow floor-to-floor heights. TCB façade systems are also a problem
with the vintage stock of TCBs. Constructed at a time of abundant and
cheap energy and when the building science of façade systems was
rudimentary, especially with respect to the new experimental systems using
glass and metal in unprecedented ways in building skin applications, the
early curtainwalls were poor performers from the beginning. Now they are
approaching 50 years of age and more. Designed with no consideration of
future retrofit the systems lack adaptive capacity and provide limited
renovation options. When part of a building renovation program, they are
most often stripped from the building and replaced with a new curtainwall
system, at considerable expense and with problematic disruption to ongoing
building operations. The unrecognized cost is embodied carbon, also
significant as the potential durability of aluminum and glass are wasted in
the process, with the aluminum generally recycled but the glass down-
cycled or transported to landfill. Moreover, the replacement curtainwall
systems are equally negligent in anticipating and facilitating the next retrofit
and renovation requirements. Case studies reveal the challenges of TCB
façade renovation, and suggest a different way of thinking about solving the
immediate renovation need, as well as how related future challenges may be
eased or avoided. The sustainability of TCBs and their façade systems are

16
found lacking in fundamental respects. At the same time, there is potential
heritage value in the vintage stock of TCBs, and the preservationist’s
perspective provides another informative lens to view these issues, where
the propensity for reclad and overclad façade renovation strategies are a
threat in compromising the historical aesthetic of this unique building type.
Chapter 8: Contribution, limitations, and future work
Contemporary TCB façade practices do not support sustainable outcomes in
tall buildings and urban habitat. They fail to provide service life
commensurate with their consumption of energy-intensive materials, adding
to a building’s lifecycle carbon footprint. They fail to provide adaptive
capacity to avoid obsolescence, to accommodate upgrades of performance-
enhancing materials and components, and to facilitate renewal strategies that
could extend service life. They share similar shortcomings to the early mid-
twentieth century curtainwall practices, and are producing latent durability
problems even as the industry struggles to deal with the legacy of those
early systems. The impacts of these failures extend to all three pillars of
sustainability: the economics of curtainwall construction, repair and
renovation stress owners, lending institutions, and ultimately, communities
and the societies they populate; the environmental impacts of embodied and
operational carbon are driving climate change acceleration, which itself
effects the three pillars; substandard façade service quality compromises
indoor environmental quality, effecting the health and productivity of users
who spend, on average, 90 percent of time indoors. Solutions are possible
but require novel trajectories to engrained curtainwall practices. These
involve expanding considerations of sustainability beyond the energy
consumed in building operations, bringing weight to such factors as:
• durability and differential durability,
• embodied carbon,
• the time value of carbon,
• the embodied impacts of materials and the importance of material
selection,
• the relationship between service life and lifecycle carbon,

17
• service life planning and strategies to extend service life,
• adaptive capacity in curtainwall systems to optimize repairability,
maintainability, and upgradability, and as a hedge against the forces
of obsolescence,
• designing for resilience as an attribute of sustainability,
• and the heritage value of the building skin.
These considerations in the context of curtainwall systems provide
opportunities for enhancing the sustainability of buildings and urban habitat.
The means to manifest these opportunities are found in the practices of
design, delivery, planning and management; contemporary curtainwall
practices are determined to be lacking with respect to these practices in
failing to account for the considerations stated above. Curtainwall system
design and delivery practices that facilitate repair, maintenance, retrofit and
renovation requirements over a perpetually extendable building service life
are the key.
More needs to be done in investigating, quantifying and articulating these
lines of inquiry to expose the nuances needed to drive a transformation in
curtainwall technology in support of sustainable buildings and urban habitat.

18

Chapter 2 — Research description
2.1 Introduction to research approach
The sustainability of contemporary curtainwall design, delivery and renovation practices
were challenged as not supportive of sustainable outcomes in buildings and urban habitat.
Key sustainability attributes were identified, their meaning and relevance developed, and
their relationship to metal-framed curtainwall systems in tall building applications
explored. These primary attributes of sustainability are introduced as the strands of
façade sustainability and discussed in Chapter 3. A select subset of the strands focuses
the inquiry on the attributes of durability, adaptability, resilience, embodied carbon and
preservation. The strand metaphor recognizes the interrelatedness of these attributes, and
the necessity that they be considered and applied as an integrated whole in a lifecycle
context. The approach is necessarily reductive to provide a manageable scope, but is
consequently flawed, an acknowledged limitation; sustainability considerations are
inherently complex, whole-systems problems. However, the findings discussed in section
9.1 informed the sustainability evaluation of tall curtainwall buildings (TCBs) and their
façade systems, and fundamentally supported the arguments in section 2.2.
Curtainwall design, delivery and renovation practices were investigated through a
methodology combining a literature review extending through multiple disciplines and
topics (Section 2.6), surveys, workshops, case studies (Section 2.5), and a quantitative
analysis of curtainwall materiality (section 4.4), but was ultimately built on three decades
of curtainwall experience that at times made it difficult to put aside predispositions and
prejudices accumulated along the way. The mental barriers, for example, to abandoning
spectrally selective and low-e coatings in pursuit of sustainability goals in the form of
recyclable material solutions is counter-intuitive to any façade practitioner.

19
The investigation of the sustainability of curtainwall design, delivery and renovation
practices extended beyond the predominant industry, professional and academic focus on
operational carbon to embodied carbon, with the recognition that as buildings become
increasingly energy efficient, embodied carbon will grow to dominate the lifecycle
carbon footprint. Consideration of embodied impacts highlighted contributory factors like
durability as a strategy to extend service life and mitigate embodied impacts. The
extension of service life required consideration of why buildings are demolished and why
they persist. The diverse causes of building obsolescence revealed that the leading cause
of building demolition was not the presumed aging and deterioration, but a failure to
adapt to changing conditions of use. In a time of accelerating social and technical change,
anticipating the potential for obsolescence becomes equally more challenging and
relevant.
Curtainwall practices were found to be problematic in several important respects, with
causation rooted in design shortcomings that manifest in the aging stock of early TCBs,
and remain in contemporary curtainwall design. Durability was identified as a key
consideration of sustainability with relevance to curtainwall technology, as a mitigating
factor to the predominance of high energy-intensity materials used in their makeup.
Durable materials and systems endure, meaning they exhibit long service life potential.
The link between embodied carbon and service life prompted consideration of strategies
to extend service life as a means to minimize lifecycle carbon footprint.
While contrary to conventional curtainwall practice, the notion of repair, maintenance
and partial renovation suggested procedures with this potential. This led to the concept of
specifying these activities through a process of durability or service life planning—in
combination with façade system design specifically accommodating repair, maintenance
and retrofit procedures—as a strategy to extend service life. The intent was to support the
hypothesis in the following section that curtainwall system service life can be extended
through renewal processes of maintenance, repair, retrofit and renovation, thereby
providing advantages over reclad as the most common form of TCB façade renovation.
This failed to account for the complicating factors investigated in Section 4.3:
§ recurring embodied carbon: maintenance, repair, retrofit and renovation
procedures add to the lifecycle embodied carbon, offsetting at least some part of
the service life gains,

20
§ and obsolescence: the reasons for building or building system replacement may
lie beyond the ability of these renewal activities to resolve.
These factors highlighted the importance of system design to minimize maintenance,
retrofit and renovation requirements while maximizing their efficiency to mitigate
recurring embodied energy impacts. This combined with the obsolescence factor to
highlight the importance of adaptability in support of extended service life, as discussed
in 5.36 and 5.37. Disruption caused by major façade renovations involving over-clad,
and especially, reclad strategies emerged as another factor in support of the hypothesis,
whether occupants are relocated during the construction process or the building remains
occupied throughout construction, with impacts discussed in Section 8.6. Disruption and
cost were identified as primary reasons for building upgrade programs excluding the
façade system, thereby delaying related performance improvements and subjecting
occupants to extended periods of substandard service quality. Both the disruption and the
delay introduced a potential impact to comfort, health, and productivity that challenged
sustainability considerations.
System removal and replacement—the reclad strategy discussed in Section 8.5.6—was
identified in the surveys discussed in Section 2.5.1 as the most common form of
curtainwall renovation despite the challenges it presents. The employment of an ongoing
process of renewal involving planned maintenance and partial renovation cycles was
conceived and investigated as a viable alternative in Sections 4.4.8 and 8.9, with the goal
of radically extending the service life of the curtainwall system, reducing the cost,
impact, and disruption of façade replacement on a 35 to 50-year cycle. The renewal
strategy also has the potential of maintaining an uncompromised service quality through
the lifespan of the system. While facade renovation practices on large commercial
curtainwall buildings provided the background for the research, the findings have
important implications for ongoing curtainwall design and construction practices for new
buildings, explored in Section 4.4.
Research on TCB façade renovation, the basis for Chapter 7 and the primary gateway
into related areas of inquiry (e.g., resilience and the literature review of socio-ecological
science discussed in Chapter 6) was notable for a relative dearth of material; renovations,
unless they involve iconic buildings, receive far less media and scholarly attention than
new construction projects. This was the impetus behind façaderetrofit.org, a tool

21
developed to facilitate façade renovation and research, discussed in Section 2.5.1.
Materials relevant to façade renovation were found in the discipline of historic
preservation, yielding articles exhibiting deep understanding of curtainwall technology,
and especially early curtainwall systems. The area of heritage and historic preservation is
largely unfamiliar to those outside the discipline, but provided another perspective to the
investigation and another venue from which to test the hypothesis and arguments adopted
here, as discussed in Sections 8.5.7 and 8.8. It was discovered that the vintage TCBs have
emerging relevance in the preservation dialogue, both as a renovation challenge and a
point of controversy as to heritage value.
The preservation literature includes relevant experience and expertise with respect to
early curtainwall technology, an expertise informed by the experience of analyzing,
repairing, rehabilitating, retrofitting, restoring and replacing façade systems on early
curtainwall buildings. This expertise seems isolated from the practice of contemporary
façade design. The feedback loops are not there; façade designers for new buildings do
not typically participate in the preservation dialogue; façade renovations are a specialty.
Few building scientists and façade consultants have had the opportunity to participate in
façade renovation projects involving these Modernist buildings, perhaps because there
have been relatively few of them to date. In addition, the preservation practitioners with
this experience seldom get the opportunity to participate in new curtainwall design
projects or in new curtainwall system development. This is a tangible manifestation of
the fragmentation dominating the building construction industry, a fragmentation that
some trace as far back as the shift away from the “master builder” project delivery system
(Taylor 2003, 40; Yates and Battersby 2003, 636). This problem is not unique to the U.S.
construction industry; a United Nations report (Cheng et al. 2008) discusses this
fragmentation and related impacts at length, and finds it a dominant factor in the
challenge presented by the greening of the building sector. Others investigate the barriers
this fragmentation presents to knowledge sharing and the development of best practices,
and the need for more collaborative design and delivery processes as a counter measure
(Alashwai, Rahman and Beksin 2011; Nawi, Baluch and Bahauddin 2014).

22
2.3 Hypothesis
The arguments developed include
1. contemporary metal curtainwall systems fail to support service life duration and
quality consistent with sustainable building performance, and
2. enhancing curtainwall system durability can extend service life and quality,
thereby amortizing embodied carbon over a longer period and resulting in a
reduction in environmental impacts, with consequent contributions to the
sustainability of the building sector,
and more specifically tests the hypothesis:
The service life of metal curtainwall systems can be extended through a
renewal strategy of planned maintenance, retrofit and renovation cycles, that
perpetuates service life, thereby providing advantages that improve building
sustainability as compared with a cyclic system replacement strategy.
2.4 Research goals and strategies
The general strategy was to develop the concept of durability and establish clear linkages
with sustainability, with the primary goal of testing these linkages in the TCB facade
system, and if present, to assess the resulting impacts on buildings and urban habitat. A
further goal was to identify strategies for mitigating impacts that compromised the role of
the TCB façade system in supporting sustainable outcomes in buildings and urban
habitat. Chapter 5 explores the rich vein of durability and its implications in curtainwall
design, delivery and renovation practice, and is foundational to the following chapters,
especially Chapters 6 (deconstructing the IGU) and 7 (TCB façade renovation).
The consideration of TCB façade renovation practices was initially burdened by the
predisposition to material and system deterioration as the prime cause of building and
building system demolition; if this process of deterioration could be stopped, the service
life of the systems would be extended. Obsolescence in its various forms was ultimately
recognized as the problem, and the lack of adaptive capacity on the façade system as the
general cause.

23
With the consideration of durability and service life as the primary drivers, the goal was
to establish the relevance of durability as a consideration of sustainability of the same
general magnitude as that of operational cycle energy consumption in buildings, and to
demonstrate that relevance through the example of the façade system, in this case, metal-
framed curtainwall systems. This is argued in Section 4.3. In addition, potential linkages
were tested and found between durability and other relevant façade sustainability
attributes identified in chapter 3, including energy and carbon, economy, maintenance,
service life, adaptability, resilience and heritage value.
Chapter 5 uses the insulated glass unit (IGU) as a vehicle to test the ideas developed in
Chapter 4. A counterfactual strategy was pursued: if a viable concept can be developed
from constraints that improve attributes of sustainability, e.g., recyclability, maximizing
service life potential, etc., then the development of alternative products adopting a
fundamentally different approach to performance—in this case an unbonded product that
can be disassembled and reassembled for maintenance and repair purposes—is a possible
strategy to address shortcomings in current materials and processes. The viability of the
IGU concept is debatable; the value was in working through the process of rethinking
product functionality and ways to provide that functionality consistent with sustainability
goals.
Chapter 6 tests for and explores a relationship between resilience and the building skin,
with the goal of establishing linkages between resilience and curtainwall façade system.
Considerations of resilience were investigated at the scale of the building façade, and at
the larger scales of building and urban habitat. Temporal scales were also considered.
Establishing the relevance of resilience considerations in façade systems revealed
shortcomings in current practice. Strategies developed below in response to these
shortcomings hold the potential to improve future practices, favorably impacting the goal
of resilient and sustainable of urban habitat.
Another primary strategy was to test and evaluate the findings of the durability research
within the context of heritage preservation, exploring the relationship between
curtainwall system renovation practices and the impact on heritage value in buildings and
urban habitat, ideas discussed in Chapter 7. Identifying the impact of façade aging and
rehabilitation on the heritage value of midcentury Modern curtainwall buildings provided
a unique perspective, and informed the consideration of future facade design and delivery

24
practices. Sustainability and resilience were identified as rooted in the behavior of a
sociocultural system. The system produces patterns and artifacts over time that become of
intrinsic value to the system’s evolution. The preservation of this heritage value is the
central focus of the historic preservation community. The goal was to reveal the linkages
between curtainwall systems and the heritage value of curtainwall buildings and the
urban habitat they populate. Such linkages may provide a new mechanism by which to
favorably impact the future sustainability of a sociocultural system.
In summary, the research strategies included the following, with the sections indicated
where they are discussed:
1. Literature review: A broad-based review was undertaken to develop a contextual
backdrop reinforcing a relationship between durability, sustainability and the building
skin, and to determine the factors that affect the service life of buildings generally,
and curtainwall systems specifically. (Sections 4.1 through 4.3)
2. Sustainability metrics: A set of relevant sustainability considerations were
developed = to test the sustainability of curtainwall design, delivery and renovation
practices. (Sections 3.4-3.5)
3. Critical evaluation: Based on the findings of the literature review, a critical
evaluation of contemporary curtainwall technology was developed with respect to
durability as an attribute of sustainability. (Section 4.4)
4. Materials analysis: Quantitative analysis of the material composition of a typical
glass and aluminum curtainwall system, and evaluation of durability attributes was
performed. (Section 4.4)
5. Concepts to extend service life: Alternative concepts with the potential to extend
service life and reduce embodied GWP of curtainwall systems were explored.
(Sections 4.4 – 4.6, 7.7 and chapter 5)
6. Rethinking the IGU: An alternative concept for an insulated glass product that does
not exhibit the problematic behavior identified in Section 4.4 was developed.
(Chapter 5)
7. Principles of façade resilience: Drawing from the literature review, general
principles of resilience were developed and tested for relevance with respect to the
façade system. The general principles were used to develop considerations of façade
resilience and design strategies to enhance façade resilience. (Sections 6.1-7.4)
8. A framework for evaluation: A framework was conceptualized and developed that
supports the evaluation and potential enhancement of façade system resilience on any
new building project or existing building renovation. (Section 6.9)

25
9. Resilience considerations: Working from the principles of façade resilience, a set of
resilience attributes and parameters were identified and tested for relevance to the
façade system. (Section 6.9.1) Strategies were developed for each attribute with the
potential to build façade resilience. (Section 6.9.3)
10. Metrics for façade resilience: Metrics relevant to the resilience attributes were
considered in support of the strategies identified to enhance resilience. The metrics
can potentially be quantitative or qualitative; numbers, ranges, or processes. (Section
6.9.2)
11. Assessment of TCB type: The sustainability of the TCB and its relative value in the
existing building stock was critically assessed. (Section 7.3.5)
12. TCB renovation considerations: A set of considerations to be used in the evaluation
of a TCB façade renovation was developed. (Section 7.4)
13. Curtainwall retrofit typology: A typology for curtainwall façade renovations was
developed, with an evaluation and case study of each strategy. (Section 7.5)
14. Rethinking the TCB energy retrofit: Current practices were assessed and
conceptual alternatives developed for façade-integrated deep green facade retrofits.
(Section 7.7)
15. Heritage perspective: The manner in which current curtainwall retrofit practices
impact considerations of heritage value and preservation was investigated. (Sections
7.5.7, 7.8)
2.5 Research questions
The following questions provided trajectory to this research and are categorized by topics
of durability, resilience, retrofit and preservation. Research methods used in deriving
answers to these questions are discussed in the following section.
Durability questions (Chapter 4)
1. How are the early examples of stick curtainwall systems dating to the mid-
twentieth century performing from the standpoint of durability?
2. How will the newer unitized curtainwall systems compare from a durability
perspective with the early stick systems.
3. How long should a building last? What is an appropriate building service life?
4. How long should a curtainwall system last? What is an appropriate façade system
service life?

26
5. What is the relationship between building and façade system service life?
6. What is the value of extending service life, service quality? What is the cost?
7. What strategies can extend service life? What are the costs and offsets resulting
from these strategies?
8. What is the relative value of a maintenance and partial renovation strategy verses
a reclad strategy over an appropriate building service life? How is this value
measured?
9. What are the opportunities for façade system design changes that would extend
service life?
10. What is the impact of façade materials that are recycled (aluminum)?
11. What is the impact of façade materials that are not recycled (glass)?
12. Is a fully recyclable curtainwall system feasible?
13. What is the importance of adaptability in curtainwall facades, and how may this
attribute be enhanced?
14. What is the financial incentive to the building owner/developer in extending
façade system service life?
Resilience questions (Chapter 6)
1. What are the term roots of resilience?
2. What is the relationship between resilience and sustainability?
3. What is the meaning and significance of resilience at the scale of the built
environment?
4. How does this meaning scale to buildings and building systems (e.g., the façade
system)?
5. Are temporal scales relevant to the concept of resilience?
6. Is resilience relevant to curtainwall technology?
7. Can considerations of resilience provide insight into better performing and more
sustainable curtainwall systems?
8. Can the façade system contribute to resilience at the broader scales of building
and urban habitat?
9. How do resilient design strategies differ from the green building practices
developed over recent years?

27
Preservation questions (Chapter 7, Sections 7.5.7 and 7.8)
1. What heritage value is recognized—within the preservation community or
elsewhere—for the mid twentieth century tall curtainwall building (TCB) type as
an artifact of Modernism?
2. If there is heritage value, what role does the building façade play in that value
structure?
3. What challenges does the curtainwall system bring to the protection of heritage
value for this building type?
4. What are the implications of façade retrofit practices on this heritage value?
5. What about the differentiation of the iconic from the vernacular; is the vernacular
salvageable and worth saving?
6. What unique perspective does the preservationist bring to the consideration of the
curtainwall systems on the select building type?
7. How does the preservationist’s perspective relate to fundamental considerations
of sustainability and resilience?
8. How can the findings from this dissertation research project be applied to the
problem of protecting heritage value?
9. In what ways can curtainwall renovation processes be improved to support
preservation goals?
10. In what ways can the preservationist’s perspective inform contemporary
curtainwall design and delivery practices?
Curtainwall retrofit questions (Chapter 7)
1. What are the different kinds of facade renovation?
2. What are appropriate criteria to evaluate the various renovation strategies with
respect to any specific application?
3. What are the different functions of the facade and how to they intersect with
retrofit requirements?
4. What are the material and system components of facade retrofit?
5. How does facade retrofit relate to other aspects of building retrofit?
6. Market considerations are potentially informative; what market opportunities are
presented by facade renovation; what are the barriers to facade retrofits?

28
2.6 Research methods
Research methods utilized include descriptive research, the use of existing data sets,
surveys and an online data collection tool, workshops and case study research.
2.6.1 Descriptive research
Descriptive research methods, largely qualitative in nature and derived from the literature
review described in Section 2.6, in combination with the author’s career experience with
curtainwall systems, were used extensively throughout to develop arguments intended to
test the hypotheses. To establish validity of results, triangulation was attempted and
achieved by 1. viewing the phenomenon (TCBs) through multiple lenses, including
durability, resilience, and reuse and renovation, 2. a conceptual exercise in rethinking the
IGU, and 3. a comparative analysis of two building types (TCBs and multi-unit
residential buildings), demonstrating convergence on the relevance of core findings
regarding embodied impacts, repairability, maintainability, upgradability, adaptability,
and extended service life.
2.6.2 Existing data sets
Select data identified in the literature review was used to substantiate key points. For
example, data was used from a publicly accessible online database on tall buildings
maintained by the Council for Tall Buildings and Urban Habitat. Unfortunately, this
database does not track information specific to the façade system, which limited its
usefulness, but most tall buildings constructed from the 1960s-onward used metal-framed
curtainwall technology. Data was used to provide some evidence as to the lifespan
characteristics of this building type.
2.6.3 facaderetrofit.org and surveys of building professionals
Working in a somewhat parallel track with PhD candidate colleague Andrea Martinez
(now Andrea Martinez, PhD) researching façade retrofit, both collecting case study data
on façade renovation projects, it became apparent that the spreadsheet Dr. Martinez was
developing to store the data was going to be inadequate for effective analysis, especially
as the combined data sources grew. Previous experience with database tools had revealed
their effectiveness in this context. Working with a small team at Enclos Corp, a database
structure was defined as described in Martinez et al. (2015). The team included web and
database development capabilities, and the structure was implemented with Enclos

29
playing a sponsorship role. The database was populated, with some USC student
assistance, with the spreadsheet data and survey results. The database tool,
facaderetrofit.org, was launched in beta version in 2014. Conceived as an open-source,
publicly accessible resource, the building community was invited to submit projects
through entry forms accessible on the website. Submissions were received, vetted, and
published. There are currently over 500 projects in the database. In addition to the
database tool itself, the concept was of a growing library of case studies, description of
basic façade renovation types with design and deliver strategies for each, a vocabulary of
facade renovation terminology, a catalog of retrofit products, guidelines, best practices,
and other resources.
To further joint research efforts and to populate the database, a survey of façade retrofits
was developed and promoted to a large network of façade practitioners and researchers in
2012. This was followed by another more refined survey in 2013. The surveys resulted in
the identification of over 300 façade retrofit projects. These methodology and results
were reported in Martinez et al. (2015; 2015a). Empirical data derived from the two
surveys is referenced in this dissertation. The exercise and results of this survey—and the
resulting facaderetrofit.org product—were valuable in providing clues as to the widely
varying impacts of curtainwall technology, particularly as manifest in the midcentury tall
curtainwall building. In addition to the methods and practices of façade retrofits, the
survey included an effort to solicit underlying motivations, goals, and relevant attitudes
characteristic of the participants in these renovation projects. The response is used to
support a claim that sustainability cannot be achieved in the absence of suitable
overriding intent. The same argument is used with respect to preservation: heritage value
is unlikely to be retained in the absence of specific preservation goals established as part
of the renovation program.
The idea of collecting data on façade retrofit projects has considerable merit, and the
quick ramp up of project entries likely reflects the potential value of the tool. Data
regarding past façade renovations is much harder to come by than data on new
construction projects, which are far more commonplace in mainstream media. There is a
limited but growing body of academic work covering case study projects as well as
diverse aspects of façade renovation, ranging from lifecycle assessment of façade
components to new product and process development for retrofit applications. A
searchable, sortable data source of existing cases could be of value to practitioners and

30
researchers alike, in filling the knowledge gap around façade renovation. The database
was a source of data for the research documented in this chapter.
A seed grant was awarded the project by CTBUH, with the money used by the University
of Southern California School of Architecture to fund student support for data
qualification and entry into the database. The project has been documented in a paper
(Martinez et al. 2015), and was presented at the CTBUH annual conference in Shanghai
in 2014. The project was also presented by the author at the annual conference of the
Association for Preservation Technology in November 2015. The current status of
facaderetrofit.org is that it remains operational, in beta, but is essentially abandoned in
terms of ongoing maintenance, and any progress on further development has ceased for
the time being. The resource has been handed off to the recently formed Façade
Tectonics Institute, where it is accessible through their website, and there is an expressed
intent to rejuvenate the project and continue its development. There is a list of issues with
respect to the websites functionality, the data quality requires additional vetting and
upgrading, and many of the projects have only minimal data at this point. Still, it remains
a useful resource as it stands, but with great further potential as the definitive resource for
façade intervention data.
The greatest value facaderetrofit.org for this research was in assessing trend data, e.g.,
appearance as the primary motivation for the façade renovation was initially something of
a surprise, which drove further research into the topic of obsolescence, much of which is
documented on Chapter 4 on façade durability. Also, the surveys established façade
replacement as the dominant curtainwall retrofit type, an important finding behind key
conclusions derived from this research.
2.6.4 Resilience Workshops
Descriptive research methods—largely qualitative owing to a lack of empirical data
regarding urban resilience—are employed to explore the hypothesized relationship
between the concept of resilience and curtainwall façade systems. In addition, a series of
workshops were conducted described following.

31
A conference series focused on the building skin1 was used to host a series of cross-
sectional studies in the form of workshops exploring façade resilience. The workshops
brought together small groups of industry professionals with interest and experience in
façade technology and practice in a focused discussion on the meaning and relevance of
resilience at the scale of this important building system. Risks to human life and property
resulting from shocks to the building skin were explored, performance parameters were
identified that link to these shocks, all with a view to identifying strategies to mitigate
these risks. Ways in which façade systems can be developed to enhance the resilience of
a building and urban habitat were also part of the discussion. Four workshops were
conducted with a total of 89 participants:
1. July 25, 2015; Chicago, IL; 26 attendees
2. October 31, 2014; Dallas, TX; 8 attendees
3. February 6, 2015; Los Angeles, CA; 22 attendees
4. April 17, 2015; New York City, NY; 30 attendees
The workshops were highly interactive, with a minimum of presentation—just enough to
establish context—and a focus on facilitating an inclusive dialogue encouraged by a
series of provocative questions and problems that were addressed both as a group and in
smaller group breakout sessions. The discourse that emerged from these workshops was
contributory to establishing the validity of the hypothesized relationship between the
concept of resilience and the building façade—a relationship that extends beyond the
usual consideration of engineering resilience. The dialogue was also instrumental in
shaping the principles of façade resilience (Table 6.1), the façade resilience factors (Table

1
Facades+ is an ongoing conference series focused on the building skin. At the time of the workshops, the conference
was a collaborative joint venture production by Architect’s Newspaper and Enclos.

32
6.2), the 10 top strategies to enhance façade resilience (Table 6.3) and many of the
metrics and strategies that populate a proposed evaluation framework (Table 6.4).
2.6.5 Case study research
Select façade retrofit cases were developed to support the arguments and findings in
Section 7.11 and 8.1, and to exemplify the façade renovation typology proposed in
Section 7.5. The case studies are documented in Section 7.5.
§ 1271 Avenue of the Americas; 1958, New York City, Wallace Harrison of
Harrison, Abramovitz, and Harris. A complete curtainwall system replacement
that claims to honor the original design intent while adding significant vision
glass area.
§ 3 Columbus Circle; 1922, 1927 addition, New York City, Willian Welles
Bosworth, Shreve & Lamb addition. Curtainwall overclad of an earlier masonry
building.
§ 330 Madison Avenue; 1963, New York City, Kahn & Jacobs. Overclad of a
vernacular TCB.
§ Javits Convention Center; 1985, New York City, James Ingo Freed; Pei Cobb
Freed & Partners. Curtainwall replacement with limited consideration for
maintaining the original façade aesthetic.
§ UN Secretariat Building; 1952, New York City, Wallace Harrison, Oscar
Niemeyer, Le Corbusier, et al. A complete curtainwall replacement of iconic TCB
building that attempts a faithful replication of the original aesthetic with
meaningful performance upgrades.
§ 60 Broad Street; 1962, New York City, Emery Roth & Sons. A discreet program
of targeted repairs for this vernacular TCB intended to extend the service life of
the original single-glazed façade by 20 years.
2.7 Literature review
The literature review was multi-disciplinary, including building science, social science,
facilities management, industrial ecology, engineering and construction, historic
preservation; and topics ranging through sustainability, resilience, service life prediction,
obsolescence, consumer products, durability planning, lifecycle assessment, construction
and demolition waste, renovation and retrofit, building materials, and maintenance.

33
There is a sparsity of literature directly addressing the durability of metal-framed
curtainwall systems, despite their predominant use in commercial building construction.
Kesik (2002) (2005) addresses durability with respect to buildings and their façade
systems in general, and is definitive with concepts of durability, embodied energy,
recurring embodied energy, and differential durability. The Athena Institute (2006) was
helpful in contextualizing the definitions and standards related to façade durability and
service life. Silva et al. (2016) directly addresses durability and façade cladding, but
focuses on the masonry related practices of Portugal and does not address contemporary
curtainwall applications. Garmston (2017, 157-207) produced four case studies
documenting successful building renewal through façade retrofit, although the focus of
the study was decision-making process and the building typology was different,
comprised primarily of low-rise institutional buildings opaque wall systems and
windows.
Reference is included to a large body of scientific work related to service life prediction,
which includes various methods and processes in support of this endeavor. Service life
prediction is a specialized scientific/engineering discipline, with extensive writings
concerning theory and methodology (Danotti et al. 2008). Silva et al. (2016) is a rich
source of this literature. The methods and processes themselves were not useful to this
research, but many of those involved in this pursuit have gained insight into the causal
forces at work in limiting service life, and those insights were harvested to some benefit.
Similarly, with lifecycle assessment the highly technical methods and processes of this
discipline were of limited value to the research thread, but the insights of those involved,
of necessity, in lifecycle thinking were of value. While decades old as a discipline,
lifecycle assessment remains as much an art as a science, in that the results of any two
practitioners can diverge widely when examining an identical project. The views of
Heiskanen (2002), for example, while controversial, had resonance with views expressed
in this report on lifecycle thinking.
Surveys on façade retrofit conducted as an early component of this research as reported in
Martinez et al. (2015) suggested that the leading driver for façade renovations was not
performance but appearance related. This was unanticipated, but confirmed by Kesek
(2002), Brand (1994) and others, and discussed as an aspect of obsolescence. This led to
a new vein of literature addressing the concept of obsolescence, both in buildings and
consumer products. Burns (2010) was particularly useful in rounding out the concept and

34
its implications in the realm of consumer products, but with many links to buildings. The
increased complexity of the causal forces behind premature service life termination, well
beyond the originally considered forces of material weathering and degradation,
significantly amplified the relevance of adaptability as a factor of façade endurance.
There is a definite linkage here to ecological science and socio-ecological systems, and
the concept of adaptive capacity as articulated in depth in that literature, and this was
explored in earlier research and documented in chapter 6 on resilience and the building
skin. It is the concept of resilience as developed in the writings of ecology and socio-
ecology science that became another predominant driver of this research. Parallel
trajectories in other sciences are used to reinforce the primary themes derived from
ecology. The review revealed no empirical studies directly linking resilience and the
façade system, but provided direction and support of the research goal of establishing
linkages between resilience and the TCB façade system and research strategies 8-11, as
discussed in Section 2.3 above. The literature review provided the basis for productive
qualitative descriptive research comparing the concepts of ecological and urban
resilience.
Information and papers of varying relevance and quality were found within the various
silos of industry and academia: the Council on Tall Buildings and Urban Habitat, Glass
Performance Days, The Aluminum Association, the Building Enclosure Council of the
National Institute of Building Sciences, the International Facility Management
Association, were found to be useful sources of information and direction, and the
research led to participation in many of these programs as both author, conference
participant and speaker.
Literature from the preservation community provided another strand to integrate in the
façade retrofit weave. The preservation disciplines have their own practitioners,
monographs, case studies, journals, conferences and proceedings, with little in the way of
crossover with other strands such as building science, facilities management, or
architectural research, much less ecology or systems theory. While common terms are
integrated into the dialogue—terms like sustainability, resilience, and performance—they
are embodied with a unique perspective; the preservation of heritage value in buildings
and the built environment. The knowledge base provided was of interest and contributed
insight to the embodied carbon benefits of building and building system reuse and the

35
threat to heritage value inherent in the predominance of façade system replacement as a
TCB renovation strategy.
Writings from the preservation community were occasionally encountered in the early
broad research of curtainwall technology. Interestingly, they were among the most
technically insightful articles, which came to make sense along with the recognition that
their insight was gained from experience with aged, and often failed, curtainwall systems.
Preservationists are provided a great opportunity to see firsthand what has worked and
not worked, what has failed and why, an experience that is often less accessible to the
new façade system practitioner. While the emphasis is primarily on fixing the problem—
in this case from the perspective of the preservationist and the protection of heritage
value—this experience affords the opportunity to consider the larger problems presented
by the symptoms they are treating. Indeed, in the dilemma presented by Modernist iconic
buildings, preservation goals sometimes focus on restoring the appearance of a facade
system at the direct expense of performance; e.g., renovations that forego performance
enhancements and replace original single-glazing with new single-glazing to preserve the
authenticity of the original design. However, in the perception of this researcher, the
preservation community exhibits an uncommon understanding of and sensitivity to the
attributes of sustainability that directly reflects their experience base. Richard Moe (2010,
loc 120), as President Emeritus of the National Trust for Historic Preservation
commented, “…preservationists are particularly adept at thinking about the long-term
survivability of buildings and how they can be carefully maintained, innovatively reused,
and thoughtfully preserved for future generations to enjoy—tasks that represent the very
essence of sustainability.”
Literature sources included the Association of Preservation Technology, an international
association which conducts conferences, published proceedings, and produces the “APT
Bulletin: The Journal of Preservation Technology.” While the APT embraces the broad
spectrum of preservation concerns, their Technical Committee on Modern Heritage
musters a focus relevant to research of the tall curtainwall building. This author
participated as a speaker at a symposium—Renewing Modernism – Emerging Principles
for Practice—organized by the APT’s Technical Committee on Modern Heritage and
Technical Committee on Sustainable Preservation and conducted during the APT 2015
annual conference in Kansas City. The symposium afforded the opportunity to interact
with some of the leading voices in the preservation of Modernist heritage.

36
DOCOMOMO is the International Committee for Documentation and Conservation of
Buildings, Sites and Neighborhoods of the Modern Movement. The Committee was
founded in 1988 with the mission of preserving the heritage of the Modernist Movement.
DOCOMOMO has since become a rich source of material for researchers through their
various events, conference proceedings and other publications, including its biannual
themed International Journal.
The International Scientific Committee on 20th-Century Heritage (ISC20C), a product of
the International Council on Monuments and Sites (ICOMOS), is another group with a
focus that encompasses the target building and system type that are the subject of this
dissertation research. Other relevant organizations include the Getty Conservation
Institute's Conserving Modern Architecture Initiative, modern Asian Architecture
Network (mAAN), and an increasing number of twentieth century heritage conservation
societies around the world intent on elevating preservation considerations of Modern
architecture. The scholars and practitioners that populate these organizations are busy
creating a rich vein of material on Modern buildings from the preservationist’s
perspective.
Relatively recent monographs produced by leaders in this field include Prudon’s
Preservation of Modern Architecture, (2008), Stein’s Greening of Modernism (2010),
and Caroon’s Sustainable Preservation: Greening Existing Buildings (2010). The
relevance to the central hypothesis of this research project—that current metal
curtainwall design and delivery practices are not sustainable—is clear from these titles,
especially the latter two. While the building façade is not the predominant focus of these
works, they all reference the building envelope at some level. Carroon (2010, 5.4, 9.2)
has sections on energy and the building enclosure, and discusses relevant topics of
maintenance, repairability, embodied energy, life-cycle assessment, and renewable
systems in the broader context of building preservation.
While including the building envelope in their discussion, these authors, as with most
authors on building sustainability, typically fail to recognize the pivotal role played by
the façade system. In articles like “Greening the Glass Box” (Ayón and Rappaport 2014)
and “Can the 1960s Single-glazed Curtain Wall be Saved?” (Jerome and Ayón 2014),
practitioners and authors Jerome, Ayón and others are among the few researching and
writing specifically on curtainwall systems in midcentury Modernist buildings,

37
recognizing the unique definition these systems bring to both the performance and
appearance of this building type. Ultimately, in a manner quite unlike prewar masonry
buildings, the renovation and preservation of a midcentury Modern building centers on
the façade—the curtainwall system.
Borrowing the perspective of the preservationist highlighted the challenge of the long-
term performance of the façade system, the threat presented by limited options and façade
system replacement, or even building replacement as possible consequences, and the
opportunity in recognizing these challenges as management problems with potential
solution in embedding preservation thinking in the design, delivery, and service life
planning of buildings.
2.8 Summary
The general strategy of investigating the concept of durability to establish links with
sustainability was successful, and the primary goal of testing these linkages in the TCB
facade system revealed strong links with materiality, service life, embodied carbon,
obsolescence, adaptability and resilience (Chapter 4). Impacts compromising
sustainability were identified and are discussed in Section 4.4, and concepts to mitigate
these impacts are explored in Sections 4.4 and 4.5. The identification of the IGU as the
weak link in the curtainwall systems (Section 4.4.6 and 4.4.7) led to the conceptual
exercise of rethinking the IGU, Chapter 5. A strong link was identified between
sustainability, resilience and the TCB façade system, leading to further investigation
documented in Chapter 6. The initial strategy of investigating the renovation of TCBs
that led to the focus in durability is documented in Chapter 7. A further goal was to
identify strategies for mitigating impacts that compromised the role of the TCB façade
system in supporting sustainable outcomes in buildings and urban habitat. The research
questions on preservation also drove consideration of the preservationist’s perspective
(Section 7.8), which informed the investigation on both durability and TCB façade
system renovation.
The literature review (Section 2.6) was the most productive research method employed,
although the façade renovation surveys (Section 2.5.3) yielded several relevant findings,
most having to do with the motivations behind the façade renovations and the lack of
engagement with sustainability strategies like resilience and embodied energy, revealing

38
a clear disconnect between expressed renovation goals and the strategies employed to
achieve those goals (Section 8.6.4). Another important and unexpected finding was the
predominance of façade removal and replacement (reclad) as a renovation strategy. The
resilience workshops (Section 2.5.4) also proved to be a valuable research method,
directly yielding the resilience framework developed in Chapter 6.
Evidence presented in the durability chapter (4) Sections 4.3 and 4.4 supports the
arguments in Section 2.2 that: 1) contemporary metal-framed curtainwall systems fail to
support service life duration and quality consistent with sustainable building
performance; and 2) enhancing curtainwall system durability can extend service life and
quality, thereby amortizing embodied carbon over a longer period and resulting in a
reduction in environmental impacts, with consequent contributions to the sustainability of
the building sector.
Testing of the hypothesis
The service life of metal curtainwall systems can be extended through a renewal strategy
of planned maintenance, retrofit and renovation cycles, that perpetuates service life,
thereby providing advantages that improve building sustainability as compared with a
cyclic system replacement strategy,
While the research discussed here is mixed-method, it is fundamentally qualitative in
nature as discussed in Section 2.5. The research approach essentially adopts the position
articulated by Golafshani (2003), with the intent of providing a quality study that helps to
“understand a situation that would otherwise be enigmatic or confusing” (Eisner 1991,
58), and of “generating understanding” as different than with a “purpose of explaining”
as in quantitative research (Stenbacka 2001, 551). The objective is to “engage in research
that probes for deeper understanding rather than examining surface features” (Johnson
1995, 4). The measures of quality in qualitative research can be regarded as credibility,
neutrality, consistency and applicability (Lincoln and Guba 1985). Testing in this context
becomes a matter of validating the “reliability, validity, trustworthiness, quality and
rigor” of the research (Golafshani 2003, 602). Triangulation is a recognized testing
strategy for qualitative research (Mathison 1988, 13; Patton 2001, 247). Triangulation is
defined by Creswell and Miller (2000, 126) as “a validity procedure where researchers
search for convergence among multiple and different sources of information to form
themes or categories in a study.” This approach has been interpreted and adopted in this

39
research. The concept of durability was investigated from multiple perspectives,
including building science, resilience and preservation, as diagramed in Figure 2.1.

Figure 2.1: A triangulation procedure was adopted as the
strategy for testing the hypothesis in Section 2.2.
The findings of this research in Section 8.1 encompass each of these perspectives.
In summary, evidence is presented that metal-framed curtainwalls are high energy-
intensity systems (Section 4.4), and that planned maintenance, retrofit and renovation
cycles are valid strategies for extending service life (Section 4.3), with the potential for
keeping critical systems like the TCB façade in perpetual service, with potential
sustainability benefits as compared with the cyclic replacement of the façade system
(Section 4.4). These renewal activities, however, are performed at the cost of recurring
embodied energy that adds to a building’s lifecycle embodied footprint, offsetting, and
potentially exceeding, the impacts of cyclical replacement. The concept is illustrated in
Figure 4.14.
The only available methodology identified to quantitatively test the hypothesis is
lifecycle assessment (LCA) (Section 3.4.1, 4.3.2), a complex assessment methodology
beyond the scope of this current investigation, but recommended for future work (Section
8.4). Numerous LCA studies are referenced in Chapter 4 involving the consideration of
service life, but none directly addressing this issue. The assessment will be complex and
the results dependent upon the definition of critical variables like service life of the
building and façade system and the frequency and scope of the maintenance, retrofit and
renovation program. In addition, LCA will only measure impacts related to energy and
carbon emissions. While arguably the leading measure of sustainability considerations,
carbon is not the only one. The sustainability advantages of the renewal versus cyclic
recladding strategy referenced in the hypothesis link to advantages of façade system
renewal identified in Chapters 4-7, including enhanced resilience, health and

40
productivity, heritage value, and minimized material waste. These factors add weight to
the core arguments in Section 2.2, but lack definitive quantitative metrics in support of
the hypothesis.
The first part of the hypothesis,
The service life of metal curtainwall systems can be extended through a renewal strategy
of planned maintenance, retrofit and renovation cycles, that perpetuates service life…
is validated by this research. The second part,
…thereby providing advantages that improve building sustainability as compared with a
cyclic system replacement strategy.
In linking service life to processes of deterioration, the hypothesis fails to account for the
wildcard of obsolescence, which can derive from many causal forces, some having
nothing to do with material or system degradation (Section 4.3.6). In addition, and as
discussed in Section 4.4.8, the design and delivery of a façade system that facilitates the
maintenance, repair, retrofit and renovation proposed as the strategy to perpetuate service
life, is likely to carry some premium of both carbon and monetary cost, creating that
potential that premature service life termination for some unforeseen reason would result
in a net loss of sustainability benefit. The concept embedded in the hypothesis is
dependent upon some length of service life where the benefits gained outweigh the initial
investment, making the condition tenuous in the early service life but likely improving as
the service life extends. Lynch (1958, 20) notes the tendency of over-capacity—as might
be employed in the form of enhanced adaptability as a hedge against obsolescence, or as
design features to facilitate maintenance and renovation processes—to be accompanied
by increased first and running costs, making unused capacity expensive. Premature
service life termination for whatever reason can definitely produce results counter to the
second part of the hypothesis, essentially disproving the hypothesis. The hypothesis
succeeded, however, in driving this inquiry.

41

Chapter 3 — Why skins: Building sustainability and
the relevance of the façade zone
The building skin combines attributes of performance and appearance like nothing else in
architecture (Patterson 2011, 226; Richards 2015, 140). The pathway to sustainability in
buildings and urban habitat winds through the façade system as the pivot point in holistic
building integration.
This chapter discusses the general relevance of the building skin with respect to building
and urban habitat—why it is important, linkages the façade system establishes between
inhabitants, building, and environment, and why the skin, as an integrative system, is a
portal to sustainability of the built environment.
Section 3.1 frames the problem in the context of the buildings and the built environment,
and the urgency of achieving carbon emission reduction from the building sector. The
opportunity represented by the existing building stock is discussed, and the role the
façade is introduced in section 3.2. The focus on metal-framed curtainwall systems and
the historical development of these systems is explained in section 3.3 (the following
chapter develops a technical description of metal-framed curtainwall technology).
Issues of sustainability are central the critical evaluation of curtainwall technology. The
integral role of the façade system in building performance and the linkage of the building
skin with sustainability is the focus of sections 3.5 and 3.6. Section 3.7 lays out the
sustainability measures selected for this research, and the rational for their
appropriateness. Sustainability considerations are developed in the context of the built
environment, buildings, and the building facade, establishing the primary considerations

42
for evaluating the sustainability of facade design and delivery practices. Chapter 3 also
identifies attributes of sustainability outside the mainstream sustainability dialogue.
Buildings are at the center of the three pillars of sustainable development—economic,
social and environmental (WCED 1987; ECOSOC n.d.), represented in Figure 3.1 and
discussed in the following section.

Figure 3.1: Relationship and interactions of the “three pillars of sustainability,” ecological, economic
and social. (Source: Bell and Morse 2003)
3.1 Building stresses: Why building-as-usual is a failure
scenario
Issues of sustainability now reside in the public consciousness as evidenced by the
ongoing public debate on critical social, environmental, and economic factors threatening
the future of cultural evolution worldwide. At all levels of government and society;
nations, states, cities, civic and private groups, and individuals are grappling with issues

43
including rapid climate change, population growth, environmental degradation, continued
reliance on nonrenewable energy sources, greenhouse gas emissions, growing economic
disparity between rich and poor, and a host of others that effect the sustainability of
social, economic, and ecological systems (IPCC 2014; Roaf et al. 2009; Meadows et al.
2004; Odum 1989).
3.1.1 Building economic stresses
Central to many of these issues is the built environment. “The nation’s economy hinges
on a healthy building sector,” (Mazria n.d.) and vulnerability of the sector was illustrated
by the Great Recession of 2008. Financial distress caused by the subprime mortgage
fiasco dramatically impacted the global economy. Housing starts remained down and
commercial real estate vacancies high for years, and recovery was slow. Widespread
high-level unemployment also persisted, with unemployment in the construction industry
at least several percentage points above the national average (Mazria 2011). Recognizing
the multiple impacts of the built environment, Mazria (2011), founder of Architecture
2030, has stated, “The road to energy independence, economic health and reductions in
greenhouse gas emissions runs through the building sector.”
The recession eased through a slow and uneven recovery. Building booms have occurred
in some regional markets, like New York City, Chicago, Los Angeles, San Francisco and
Seattle (Richter 2017). This construction market activity, however, has focused largely on
new building construction, and much remains to do in converting existing buildings to
sustainable building goals (Amann 2017).
3.1.2 Building carbon stresses: Energy consumption and greenhouse
gas (GHG) emissions
It is not just the economy, however, that is impacted by the building sector.
Environmental impacts resulting from the massive pumping of greenhouse gases into the
atmosphere are driving anthropogenic climate change and altering global climatic
conditions, warming the earth, melting glaciers that feed the world’s waterways and
raising sea levels, and producing superstorms of increasing strength and frequency (IPCC
2014; McKibben 2012; Rahmstorf et al. 2007). People new to these considerations are
often surprised to learn that buildings in the U.S. consume nearly half of all energy,
almost as much as the transportation and industrial sectors combined. Buildings also
consume over 75% of all electricity generated in the U.S., and produce nearly half of all

44
GHG emissions (Architecture 2030 2017). Again, both debate and action have emerged
at levels as represented by such organizations as 2030 Architecture and their various
initiatives targeting carbon neutrality in buildings. Various groups including the
American Institute of Architects (AIA) have embraced the Challenge. The AIA has
responded with the organization of architectural firms in embracing the program, which
includes progress monitoring and transparent reporting. New York City has responded
with a comprehensive and ambitious plan PlaNYC, and many cities and municipalities
have developed their own sustainability plans and initiatives.
Operating energy consumption in new buildings, as the leading contributor to GHG
emissions from the building sector, quickly became the predominant focus of the green
building dialogue.
3.1.3 Building social stresses: The challenge of urbanization, health
and productivity
The majority of the world’s population reside in urban areas, projected to reach 66
percent by 2050 (World Bank 2017). In North and Latin America, over 80 percent are
urban dwellers. Urbanization and population growth are projected to add 2.5 billion
people to the world’s cities by 2050. (U.N. 2014, 1) David Harvey (2014, 29) has written,
“We are, in short, in the midst of a huge crisis—ecological, social, and political—of
planetary urbanization without, it seems, knowing or even marking it.”
Urbanization is dramatically reshaping culture, technology and the built environment.
Urban environments in mid-twentieth century North America were largely workday
habitats, comprised primarily of office buildings, that emptied out in the early evening as
commuters returned to their suburban dwellings (Roaf et al. 2009). This has changed
rapidly over recent years with the construction of multi-unit residential buildings in dense
urban environments (CTBUH 2011).
3.1.4 Building energy retrofits: The case for existing buildings
Existing buildings are estimated to outnumber new buildings by over 100 to 1
(Lockwood 2008), and represent the biggest opportunity in reducing energy consumption
and greenhouse gas emissions produced by the building sector.

45
Green codes, standards, and practices continue to emerge and to be adopted at various
levels of governance and operations. Building and building product-rating systems have
developed in response to the challenges posed by the building sector. Energy Star is an
energy focused labeling system that extends from products and appliances to buildings.
Started in 1992, ENERGY STAR is a joint program of the U.S. Environmental Protection
Agency and the U.S. Department of Energy. The organization claims $7.8 billion in
commercial building energy savings through their program in 2015 alone, $144 billion
since 1992 (Energy Star n.d.). As of 2016, over 29,500 commercial facilities have earned
the Energy Star, using on average 35% less energy than their lesser peers.
The U.S. Green Building Council (USGBC) launched the Leadership in Energy and
Environmental Design (LEED) green building certification system in 2000. As of
September 2016, the USGBC claims nearly 32,500 LEED certified commercial buildings
in 162 countries (Shutters and Tufts 2016), not a strong uptake considering the magnitude
of problem posed by the commercial building sector, where the U.S. Energy Information
Administration (EIA) estimated 5.6 million commercial buildings in 2012 (EIA 2012).
While very few of these buildings are categorized as large (over 100,000 square feet of
floor area) they represent one third of total commercial floor space; fixing a few large
buildings can be an effective strategy to change building sector energy performance.
Much of the focus of the various rating and certification programs, as with LEED, has
been on new buildings and new building construction. It is apparent, however, that the
existing building stock provides the greatest opportunity for transformation of the sector.
The EIA (2012) characterizes the U.S. commercial building stock as middle-aged, with
approximately half built before 1980; the median building age in 2012 was 32 years.
In New York City, the impact of buildings dominates the environment; buildings are
responsible for 75% of the city’s carbon emissions, 94% of electricity use, 50% of solid
waste from building construction and demolition, and 85% of water use. Planners
estimate that approximately 85% of the city’s existing buildings will still be standing in
2030 (City of New York 2011, 169, 204). What percentage this will represent of the total
building stock in 2030 depends on an uncertain future of new construction, but clearly,
they will be a determining factor in the overall energy efficiency of the city’s building
stock. With nearly a million existing buildings this is a formidable challenge. However,
the total square footage represented by these buildings is concentrated in just 2 percent,
or about 15,000 properties over 50,000 square feet that consume 48% of total energy use

46
in the City (NYC 2017). Goals for future reductions in energy consumption and related
carbon emissions must be built on a foundation of improvements to the existing building
stock. New York City has initiated its “80 x 50” plan, with the goal of 80 percent
reduction in GHG emissions by 2050 (City of New York n.d.). Other organizations have
responded to the opportunity presented by existing buildings. Architecture 2030 has
integrated building renovation into the carbon reduction targets for its initiative to assure
that renovations of existing buildings at least match new construction (Architecture 230).
The USGBC developed LEED for Existing Buildings: Operations & Maintenance,
focused on existing building performance. LEED v4 for building design and construction
includes standards for new construction and major renovations.
Building renovation has historically approximately equaled new construction (EIA n.d.).
Should this trend continue, Architecture 2030 projects that fully three quarters of the
building stock will be comprised of either new or renovated buildings by the year 2035.
This quantifies the opportunity to fundamentally transform the commercial building
sector in the relatively near future, with renovation of the existing building stock as a
critical component. It is estimated that renovation of existing stock is related to 86% of
the U.S. annual building construction expenditure (Landsberg et al. 2009). Building
renovations, however, take many forms and are undertaken with varying motivations.
Some renovations may not improve a building’s patterns of energy consumption at all;
some may even make it worse. A new form of building renovation has emerged as part of
the green movement in the building industry, what is commonly referred to as a building
energy retrofit, with the objective of improving energy performance. Most of these
renovations tend towards the cosmetic, and even the energy retrofits fall short of optimal
results. A deep-energy retrofit, as a more specific form of building renovation, involves
consideration of the façade system in the renovation program (Hart et al. 2013).
3.2 Building types: Why tall?
3.2.1 Commercial Building Typology
A challenge presented by the commercial building sector is that most buildings represent
unique cases customized to such considerations as site, use, location, zoning and building
code regulations, aesthetic considerations, number of stories, applied building
technology, and myriad other factors that yield a wide assortment of building types

47
regardless of categorization criteria. Consequently, categorizing the building stock is
somewhat challenging, and as with any classification scheme, different criteria can be
used as the basis for distinction. Any of the considerations mentioned above, for example,
can conceivably be used in various combinations in a scheme for categorizing buildings,
with the goal of establishing groupings appropriate to some program of analysis. Yet any
meaningful classification scheme in this context will likely produce a wide range of
types. The Energy Information Administration’s Commercial Buildings Energy
Consumption Survey (CBECS) 2003, for example, categorizes the nearly 5 million
commercial buildings in the U.S. on the activities of use, aggregating over 100 identified
activities into 14 categories. This classification scheme has some relevance to retrofit
considerations: vacant buildings and warehouses, for example, will have far different
patterns of energy consumption than occupied office or retail buildings.
Buildings can be classified by height, as does the Council on Tall Buildings and Urban
Habitat (CTBUH), by size in terms of floor area, or any number of other criteria. Some of
these variables are also important considerations in determining a façade retrofit strategy.
A high-rise building located in an urban environment, for example, will present different
challenges than a single-story building in a suburban office park. The type of technology
employed in a building is a fundamental consideration in a retrofit program, particularly
with respect to the structural system, mechanical systems, and the building envelope
itself. Single story masonry buildings, rather obviously, present an entirely different
retrofit challenge than do tall buildings. Most contemporary tall buildings are skinned
with curtainwall cladding systems, with most of these making a predominant use of glass.
Low-rise masonry structures, in comparison, frequently incorporate punched windows in
masonry walls. Retrofit considerations will vary substantially between these types of
buildings.
It is useful to explore retrofit considerations within the context of an appropriate building
type. The point here is not to develop a new categorization scheme for commercial
buildings, but to identify a discrete building type that will allow for a focused and
meaningful analysis of all components of a facade retrofit program in the specific context
of that building type. It is proposed that the most relevant consideration in determining
the target building type is the facade technology employed in the building envelope.
Other factors may also be appropriate in developing a more focused building type for
examination.

48
3.2.2 Tall Buildings
There is no exact definition for a tall building (including skyscrapers, high-rise, and
supertall buildings. CTBUH has established itself as the arbiter of building height and
assumed the cataloging of tall buildings and tracking of tall building technology (CTBUH
2017a). Regarding tallness criteria, they suggest an approximate threshold of “perhaps”
14 or more stories, and over 50 m in height. CTBUH tracks statistics concerning tall
buildings worldwide over 200 m. The CTBUH goes on the qualify “tallness” as a relative
function of;
1. context: a 20-story building in the middle of a Midwest cornfield will exhibit the
property of tallness, the same building in the midst of Manhattan's Midtown
district may appear dwarfed,
2. proportion: slenderness, the ratio of height to width, is an attribute of a tall
building, whereby a 20-story building with a small footprint will appear tall,
perhaps even regardless of context, a 20-story building with a huge footprint will
not appear tall even in the middle of a cornfield, and finally,
3. technology: certain building technologies are associated with tall buildings, such
as vertical transport and structural wind bracing.
Supertall buildings are more succinctly defined as buildings over 300 m (984 ft) in
height. The pursuit of ever-increasing tallness recently motivated CTBUH to create the
new category of megatall at over 600 meters. There are currently 3 supertalls, and the
Council predicts 8 by 2020.
Most early tall structures functioned as office buildings, one of the designated CBECS
building types. By the turn of the twenty-first century, tall building design had evolved to
multi-use functionality, with many high-rise structures incorporating some combination
of office, retail, residential, sport, and entertainment facilities. In addition, increasing
numbers of tall buildings were being constructed as residential towers.
Most tall buildings are concentrated within the dense urban centers that comprise the
great cities of the world. Unfortunately, CTBUH does not track data on the façade system
typologies of tall buildings, but the large majority of tall buildings starting in the early
1960s incorporated curtainwall technology. TCBs emerged from a post-war building
boom in Europe and North America that intersected with emergent building technology
and the need for additional office space in the rapidly developing cities (Wigginton 1996,

49
96). A new crop of speculative building developers recognized the intersection as a
lucrative opportunity for a new building type, the steel-framed high-rise curtainwall
building. Wigginton (1996, 65-98) notes that early curtainwall technology was unrefined,
the design, fabrication, and installation often wanting in quality and craftsmanship, built
during a period when energy was cheap and there was little concern for occupant
comfort. These early tall buildings were almost invariably single-glazed, with no thermal
break between the façade system and the building interior (Ayon and Rappaport 2014).
The relevance of tall buildings is partially in their extensive and increasing application–
through the twentieth century to the present day–and the resulting environmental,
economic, and social impacts, but also in the space they occupy in the public
consciousness. Skyscrapers have from the beginning been associated with economic
growth, prosperity, and a global modernism. Scott Johnson in Tall Building: Imagining
the Skyscraper (2008, 11), gestures to both the past and future evolution of this building
type, “Paradoxically, as the building type [tall buildings] continues to develop greater
levels of complexity, encompassing subtler technologies, and designed to address specific
and fundamentally different cultures, the image, that is to say, the idea, of the skyscraper
in the public mind seems to become simpler, more omnipresent, and more consumable.”
Skyscrapers have inspired numerous books of both theory and practice, movies and other
artistic musings, and careers, yet have also been controversial from their initial rise.
Critics continue to predict the demise of the tall building as an unsustainable building
form. In Adapting Buildings and Cities for Climate Change, in a chapter titled “The End
of the Age of Tall Buildings,” Roaf et al. 2009, 237), declares, “With the arrival of the
global economic slump in 2007/08, so began the end of the age of tall buildings.” The
chapter catalogs many of the problems and concerns unique to high rise buildings, and
renders a rather apocalyptic vision of the future of this building form. The Great
Recession of 2008 curtailed high-rise construction projects in many regions, yet the
rebound was swift in markets like New York City, followed by Miami, San Francisco and
Seattle in North America.
The construction of tall buildings has entered a dramatic boom period, as documented by
the Council for Tall Buildings and Urban Habitat (CTBUH 2017). The number of tall
buildings, along with their size and height, has been escalating since the late 1990s.
Record years include 2014-2016, with new records predicted in 2017 and 2018. Notable
statistics for 2018 include:

50
§ 128 completions over 200 m, a record
§ 1,168 buildings over 200 m worldwide; 111 over 300 m
§ 66% of completions were in China
§ 54 cities in 19 countries with completions
§ 52% office; 15% residential; 31% mixed-use
CTBUH reports document that while the construction of new tall buildings has shifted
dramatically from North America and Europe to Asia and the Middle East, increasing
dramatically in both quantity and height, the majority of older tall buildings are
particularly abundant in North America. Developing markets will soon enough become
developed markets. The construction community must recognize the inevitable need, and
plan for the future façade retrofit of new tall buildings. Markets now experiencing a tall
building boom have the opportunity to build better performing and longer lasting
buildings that anticipate and accommodate the need for future facade retrofit. Two
important predictions regarding these newer tall buildings can be made with some
certainty (Patterson et al. 2012, 214):
1. They will be around for many decades; and
2. They will require renovation to the building facade during the lifetime of the
building.
Roaf et al. (2009, 259) goes on to comment, “The thrill of tall buildings has, to a large
extent, been dampened for New Yorkers, and many others around the world, by the
events on and after 11 September 2001.” In fact, the CTBUH database records the
completion of 63 buildings 150 m tall or more have been completed in New York City in
the wake of 9/11, a full 25 percent of the current total in the city. Globally, the number of
buildings over 200 m has increased by 484 percent since 2001, to 1,428.
It may still be premature to predict the end of the skyscraper. The trend of more and taller
buildings continues through this day, although major geographic shifts in construction
have altered the patterns of new tall building construction among nations. There are good
reasons, however, to question the sustainability of this trend, and of the tall building as a
sustainable building type. The Great Recession did evidence a vulnerability of large and
costly construction projects to economic conditions. A peak could come at any time,
followed by a gradual decline in applications that ultimately renders tall buildings as
mere artifacts of the built environment. Roaf et al. (2009) link tall buildings with a

51
variety of problematic phenomenon ranging from psychological problems for occupants
and associated health care costs, to high construction, operation, and maintenance costs.
The authors are essentially arguing against the future promotion and construction of tall
buildings. They take no position on what should be done with the many existing
buildings. If these assertions prove valid, a path forward is to repair, rehabilitate, adapt
and ruse these buildings in an attempt to correct or mitigate the problems they have
identified. Stein (2010, 34) claims that upgrading and reusing rather than replacing
buildings can save the equivalent of 4 billion gallons of oil per year in construction
processes, which he further equates to “removing about 10 million cars from the road.”
If tall buildings are not, in fact, inherently unsustainable, then sustainable solutions may
yield from these remedial efforts, as well as from future developments in the design and
technology of this building type.
While the CTBUH reports document that the construction of new tall buildings has
shifted dramatically from North America and Europe to Asia and the Middle East, the
majority of older tall buildings are particularly abundant in North America. Regardless of
location, most of these buildings are clad using curtainwall systems and will ultimately
share the need for facade retrofit. The average age of the top 10 tallest buildings in a
region is an indicator of the imminent need for retrofit. In 2011, developing countries like
Vietnam, Qatar, and Panama had the youngest average at 3 years, the U.S. had the oldest
at 32 years (CTBUH 2011a). The extensive need for facade retrofit will emerge in the
U.S., but will follow in other regions in coming decades. The opportunity is to establish
guidelines for sustainable facade retrofit from the experiences of these early retrofits that
can influence the many to follow, and perhaps inform new tall building design and
construction practices such that future facade retrofit requirements can be minimized and
more easily facilitated.
3.3 The rise of the tall curtainwall building
Many discrete elements developed and converged to lay the foundation for a stunning
post World War II building boom that reshaped, and in some cases created, the skylines
of the urban metropolis. Herein lie the roots of tall buildings and the curtainwall systems
that were so integral to this building type.

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3.3.1 Skin and bones: A new building cladding technology for the
post war building boom
Many discrete elements developed and converged to lay the foundation for a post World
War II building boom that reshaped, and in some cases created, the skylines of many city
centers. Since the time of its inception, curtainwall technology has been applied to a
remarkably wide variety of building types as categorized by form and function.
Nonetheless, the advent and development of curtainwall technology is and continues to
be inextricably linked with tall building design and construction. With origins in the early
half of the twentieth century, tall buildings emerged as a dominant construction strategy
in the mid-twentieth century that continues to this day (CTBUH 2016).
Glass was in widespread use as an architectural material in window applications by the
eighteenth and nineteenth centuries in Northern Europe (Wigginton 1996). A broader
vocabulary of use gradually emerged in the late eighteenth century and into the
nineteenth as represented in the great iron and glass conservatory structures. The
Industrial Revolution was yielding advances in glass fabrication that were paralleled by
new developments in cast and wrought iron production. This yielded an enclosure
technology that diverged radically from the masonry construction characteristic of the
time; a building technique comprised of discrete framing and cladding systems. The
metal frames eliminated the need for continuous load-bearing walls, creating “windows”
in the structural framing system. Innovators such as Joseph Paxton, J.C. Loudon, Richard
Turner, and Decimus Burton were designing structural systems of iron frameworks that
were subsequently clad in sheet glass, thus expressing structure and skin as separate but
related enclosure components (Patterson 2011, 4).
This development was a fundamental prerequisite to the buildings produced by the
Chicago School in the 1880s and 1890s, as well as to the Modernist movement which
followed around the turn of the century. William Jenney, educated in Europe and
working as an architect in Chicago, developed a framing technique for multi-story
construction. His 8-story Home Insurance Building (1885) is widely regarded as the first
skyscraper (Giedion 2009, 207). The technique yielded more efficient building structures
weighing roughly half of a conventional masonry building of similar configuration,
greatly facilitating the verticality of emergent construction practices.

53
Meanwhile, the Modernist vision was in ferment, partially inspired by these gradually
emerging new materials and building techniques, slowly coalescing in a theme of glass
and steel as propagated by visionary architects including Walter Gropius, Mies van der
Rohe, Bruno Taut, and inspired by author–visionary Paul Scheerbart. Utopian
movements centered on glass architecture were increasingly active in the early years of
the twentieth century. Van der Rohe envisioned and expressed the glass skyscraper with
the design for the Friedrichstrasse in Berlin in 1921 (Mertins 2014, 58-82). The design
was unbuilt, exceeding technical capabilities of the period, but was widely publicized and
greatly influenced the international building design community. Several decades would
pass, however, before these visions were manifest, most notably in such iconic buildings
by Van der Rohe as 860-880 Lakeshore Drive, 1949, Chicago; Lever House, 1952, New
York City, and the Seagram Building, 1958, New York City.
The push and pull of market demand and technological invention was engaged by the
early Modernists. The dynamic reveals a complex interplay of forces that often yield a
technological capability that is only very gradually embraced by the marketplace and
assimilated into practice. The new structural framing systems eliminated load-bearing
perimeter walls, freeing the designer to depart from the use of masonry materials to
provide enclosure. Alternate methods were slow to develop, however, and the use of
heavy masonry infill walls with steel structural systems remained common practice
through the first half of the twentieth century, with only a very gradual emergence of new
techniques. The vast majority of multi-story buildings produced during the first half of
the twentieth century utilized masonry construction for the exterior walls.
Regardless of the heavy and somewhat ponderous construction, building height continued
to increase following the first skyscrapers to be constructed in Chicago and New York at
the turn of the century; the great press for increasing height had begun, driven by the
commercial real estate market push for maximizing leasable area on a given footprint. In
addition to the new structural framing techniques, important parallel developments in
refrigeration and lift technology enabled this vertical progression; elevator systems
capable of fast and efficient vertical transport were in place by the late nineteenth
century; William Carrier introduced his first whole-building air conditioning system in
1911. These combined technologies ultimately enabled the sealed high-rise office tower,
whereby natural ventilation was replaced by centralized heating, ventilating and air

54
conditioning (HVAC). This eliminated the need for operable windows, facilitating the
simplified cladding systems that were to emerge in the mid twentieth century.
Curtainwall was the term that emerged in conjunction with the building cladding
technology of the mid twentieth century. The origin of the term is likely in medieval
castle construction, referring to the enclosing wall that spanned between adjacent towers
or turrets (Hughes 1994, 134). This is consistent with the enclosing non load-bearing
masonry walls that spanned between building columns even as steel framing systems
came into use. The term took on new meaning when applied to the emergent steel and
glass–and later aluminum and glass–cladding systems in the twentieth century, where
many assume the term derives from the manner in which they are hung on a building
rather like a curtain. Murray (2009, 20) cites the obscure Boley Building by Louis Curtiss
(Kansas City, 1908) and the Hallidie Building by Willis Polk (San Francisco, 1918) as
the earliest examples of curtainwalls in the U.S. Both projects feature steel-framed glass
panel facades that are separated and steped away from the building structure.
Among the first tall buildings clad in what can be regarded as vintage TCBs were the two
residential towers at 860–880 Lake Shore Drive in Chicago (1951, Mies van der Rohe).
While these earliest curtainwall systems utilized steel as a façade framing element, an
aluminum industry was developing that would soon revolutionize the practice.
Affordable sources of aluminum billets were used to drive new industrial press
technology to deliver economical, highly customized sections of linear material through a
process of extrusion (Yoemans 2001, 13-18). The heated aluminum billets are pushed
through a die conforming to the desired section properties. The process proved ideal in
facilitating the façade framing sections required to clad the exterior of the new high-rise
buildings, and remains the dominant form today.
Another significant development occurred in the 1960s with the advent of a new flat glass
production technique (Wigginton 1996, 64-5). The float process, as it is called, was
developed by Sir Alistair Pilkington, an employee of but no relation to the Pilkington
brothers whose glass production company bearing their name was to become among the
largest international glass producers. Alistair discovered that by floating molten glass in a
continuous ribbon over a bed of molten tin, a highly uniform flatness could be achieved
with excellent optical properties on both surfaces of the sheet without need for additional

55
processing. The process proved highly efficient and quickly revolutionized glass
production, enabling a new glass architecture in the process.
The economical supply of glass was rapidly adopted by building marketplace, producing
a shoddy version of Scheerbart’s vision of crystalline cities (Gibbons 2016). While stone,
metallic, and composite panels were common, glass rapidly became the predominate
infill material in curtainwall systems. Soon, glass monoliths were rising from the urban
centers, characterized by a monotonous uniformity in the building skin. This visual affect
was heightened by the early introduction of mirror coatings to the gridded glass surface to
mitigate the problematic solar behavior of clear glass in the building skin, which quickly
became a comfort issue with the occupants of the early glass towers. Suddenly the
dominant aesthetic was not the transparency envisioned by the early Modernists, but
mirrored reflections rendering the building envelope quite opaque from the outside.
3.3.2 A Vertical Nexus
By the mid-twentieth century the post war building boom was ratcheting up. The
Modernist vision had been largely absorbed by the design community, and a new
aesthetic of transparency and form embraced. An enabling infrastructure of material
suppliers and fabricators was in place, eager to promote an abundant supply of
inexpensive framing and cladding materials. Lift and HVAC systems had also increased
in sophistication, capacity, and cost-effectiveness. Several prominent TCBs had received
widespread attention. But the catalyst that coalesced these elements into a new building
type was the recognition by the real estate community of TCBs as a means to maximize
leasable floor area (Wigginton 1996, 96-97. The minimal depth characterized by these
new “skin” systems represented a significant advantage when the extra inches of floor
dimension were multiplied by the full perimeter of the floor plan, then by the number of
floors, and again by the time factor or rental period. The speculative high-rise office
building was born, and curtainwall was the new skin.
3.3.3 Curtainwall technology
The consideration of retrofit requirements for TCBs is informed by an understanding of
the technology of curtainwall systems and its relation to the evolution of tall buildings.
The following provides a brief historical context to the technology.

56
Curtainwall facades are most simply defined as non-load bearing exterior wall systems,
engineered to span between floors and transfer all lateral and gravity loads to the building
structural framing system (Kelley and Kaskel, 1996, 57). One curtainwall type is the
metal-framed sometimes referred to as metal and glass, or aluminum and glass. They are
most commonly built up from extruded aluminum framing elements, although steel
frames are not uncommon in early applications, that support various infill cladding
components, predominantly glass, but also various opaque materials ranging from stone
to composite insulated panels. Curtainwall buildings are characterized by the extensive
use of glass as a cladding element, and curtainwall technology is integral to the building
strategy that produced the all-glass skyscraper and the sealed building envelope with
centralized HVAC systems as the only source of ventilation. These new lightweight
cladding systems paired with evolving tall building practices to enable a new building
type in the mid twentieth century, the striking glass towers referred to here as tall
curtainwall buildings (TCBs). Highly glazed curtainwall buildings came to dominate tall
building construction in the 1960s (Wigginton 1996, 96-97).
Curtainwall is not limited to application on tall buildings; many low and mid-rise
buildings, large buildings in particular, make use of the technology. Most of the findings
of this research apply to any curtainwall clad building regardless of its height or number
of stories, but the particular focus is their application on tall buildings. Unique
considerations exist with respect to the façade retrofit of tall curtainwall buildings, most
having to do with their extreme verticality and the challenges that presents in accessing
the building surface, and also their frequent location in dense urban environments.
However, many of the findings in summary Chapter 8 are applicable to the broader range
of building stock bearing curtainwall facades, all of which will ultimately share the need
for retrofit. Best practices for façade retrofit are sometimes general in nature, applying to
a broader spectrum of retrofit applications. Fundamental sustainable practices of reuse
and recycling, for example, may be applicable to all retrofit applications. The tighter the
building type classification, the more detailed and finely tuned the practices may become.
The research and analysis presented here purposefully limits focus to TCBs. This
building type is a particular problem with respect to performance and façade renovation.
The façade technology that emerged in response to the new speculative office building
was a simplified, stripped-down, commoditized version of the intricately detailed
explorations launched by the early Modernists. Maximizing profit was the overriding

57
priority with little consideration for performance (Wigginton 1996, 96-97). Thermal
behavior was not a consideration: energy was cheap, and the lessee paid the cost anyway.
Acoustical performance did not really matter; urban areas emptied out in the early
evenings as commuters returned to the suburbs. The office buildings stood empty through
the evening and night. As a result, framing systems were typically thermally unbroken
and single-glazed; it was not until after the oil crisis in the early 1970s that double-
glazing came into increasing use (Sommer 2011). The Lawrence Berkley National
Laboratory (LBNL) estimates that $40 billion is lost annually through inefficient
windows in the U.S. (Selkowitz, 2011).
Wigginton (1996, 3.96) refers to the “intrinsic weaknesses in technology and
performance which these walls incorporated.” Both glass and aluminum are extremely
poor insulators. If one were to set about designing an enclosure system to maximize
building energy consumption per unit of plan area, the high-rise all-glass curtainwall
building may well be the optimal building form. In fact, Wigginton and others have
characterized these new curtainwall skyscrapers as giant heat sinks, optimally designed to
facilitate heat transfer through the uninsulated glass and aluminum skin, and amplifying
energy consumption through a high surface-to-volume ratio characteristic of a tall
structure. Thus, while TCBs are a relatively small percentage of the existing building
stock, they consume more than their fair share of energy (DOE 2010). Even
contemporary LEED rated TCBs have been revealed as characteristically consuming
more energy than pre-war generation with deep floorplates, masonry walls providing
thermal mass, and high windows to provide daylight (Navarro 2009). Some question
whether highly-glazed facades can be regarded as green (Narain 2013; Patterson and
Vaglio 2011a; Straube 2008).
3.3.4 Unnatural ventilation
Operability involving movement and kinetic reconfiguration in a building structure or
envelope is invariably a challenge in the building arts because of the resulting increased
complexity and cost. Operable windows in the building façade are no exception. The new
whole-building HVAC technology available in the mid twentieth century provided a
radical solution eagerly embraced by façade contractors: the completely sealed building
envelope. The building interior could be thermally controlled without the need for
localized user operability. This vastly simplified the curtainwall system requirements, but
virtually eliminated natural ventilation as an environmental control strategy in this

58
building type. There are many benefits to natural ventilation, and green building
designers frequently desire to integrate a strategy of natural ventilation into the facade
design. Operable vents (windows) in TCBs are a particular problem because of the
greater wind speeds at higher elevations, and the difficulty in controlling mechanical air
supply as vents are randomly opened and closed by occupants.
3.3.5 The aging modernist facade
The looming need for building renovation on a massive scale is widely recognized as an
infrastructure problem that should be addressed with the same appropriate urgency as the
nation’s transportation systems, power grid, telecommunications network, and other
critical technical social support systems (Van Cleave 2017). This includes TCBs, and on
this building type, inclusion of the façade system is a must for a deep energy retrofit. The
urban environment has come to be increasingly populated by tall buildings. The vintage
stock of TCBs built up through the 1970s, are now approaching 50 years of age and
more. The argument that the performance of older buildings and building products is
often superior to their contemporary counterparts is not relevant to this building type; the
early tall curtainwall buildings in particular were poor performers to begin with, and age
has further compromised their efficiency (Brock 2005 96; Ayon and Rappaport 2014).
Some form of facade intervention will ultimately be required.
As discussed previously, the building sector is a dominant factor in energy consumption
and carbon emissions, and tall curtainwall buildings are a significant contributor to this
problem. While no agencies monitor the energy consumption of this specific building
type, the EIA notes that while the commercial sector is dominated by small buildings,
large buildings are generally far more energy intensive per unit area (EIA 2008). In
contrast to smaller commercial buildings, the percentage of consumption in larger
commercial buildings greatly exceeds the percentage of buildings. For example, less than
one percent of buildings are larger than 200,000 square feet in size, but these buildings
consume more than one-quarter of total energy (EIA 2008). This statistic points to the
opportunity in improving energy consumption in large commercial buildings, and while
these are not exclusively TCBs, they fall within the general category of large buildings.
Some of these older facades have deteriorated significantly, to the point that they may
even present a life-safety threat to the occupants and to the public from potential
envelope breaches and falling debris. New York City has an aggressive code

59
requirement—Façade Inspection Safety Program (FISP), known as Local Law 11—that
buildings over 6 stories undergo a professional facade inspection every five years.
Temporary protective canopies over public walkways immediately adjacent to a
building's facade are a common sight in Manhattan to accommodate these inspections or
required repairs. In addition, codes and standards have undergone substantial change over
past decades. These older facades were not designed to current wind and seismic loading
requirements that can affect everything from anchorage of the curtainwall system on the
building structure, to the movements the systems are required to accommodate under
various loading conditions.
While the vintage TCBs were not great performers to begin with, their patterns of energy
consumption, carbon emissions, and the comfort provided occupants is far below current
standards of building practice (Ayon and Rappaport 2014). As predominantly office
buildings, thermal and acoustical shortcomings were more or less tolerated. As people
have come to spend increasing time in the office environment and while their
expectations of comfort have expanded, so have these building facades continued to
deteriorate, providing even further compromise to comfort and energy performance. It is
well documented that comfort plays an important role in worker health and productivity,
and there is significant value in providing a functionally comfortable environment for the
workforce (Browning et al. 2012). Excessive energy consumption and related emissions
characterize the commercial building sector, and especially this building type (Section
8.3).
The result is that many of these buildings have fallen out of BOMA class A building
qualifications to class B or C, significantly limiting property values. Facade retrofits of
tall curtainwall buildings represent a potential contribution to the greening of the built
environment. The great challenge is that the façade retrofit of TCBs tends to be both
expensive and disruptive, and the owners of class B and C properties cannot justify the
economics of deep green building retrofits involving the façade system. As the need for
the eventual renovation of these curtainwall systems went unrecognized, they present few
options for retrofit. The majority of major curtainwall renovations in TCBs to date have
involved complete façade replacement (Martinez et al. 2015). The cost and complexity of
this undertaking raises the possibility of building replacement as a viable alternative
(Browning et al. 2013), creating the threat of building demolition and reconstruction with

60
the associated environmental impacts, a challenge to sustainable outcomes from building
renovation. Chapter 7 explores the issues of the façade retrofit of TCBs in depth.
3.3.6 It’s not all about glass
The performance attributes of the facade are not limited to the glass, however, even in a
highly-glazed curtainwall system. These systems are assemblies comprised of panel
cladding materials and framing systems, and it is the assembly that is most important to
consider when evaluating performance. The panel materials are installed in the frame
with a combination of sealants and gaskets to control moisture and air. Air infiltration
and water penetration are the prominent overall considerations in curtainwall
performance, and both were common problems in early curtainwall buildings (Brock
2005, 96; Ayon and Rappaport 2014). Air infiltration through the curtainwall system is a
primary contributor to excessive building energy consumption and compromised
occupant comfort. The integrity of the weather barrier provided by the curtainwall is
reliant upon various combinations of gaskets and sealants. Poor design practices,
compromised fabrication quality, and substandard installation can significantly
compromise performance. Even well designed and constructed curtainwalls, however,
will exhibit compromised performance as seals age and overall system fitness
deteriorates over time. Chapters 5 and 8 discuss the likelihood that new curtainwall
systems are vulnerable to similar problems as now being experience with the older TCBs.
They are not designed for maintenance or retrofit. Once installed it is virtually impossible
to inspect, repair or replace these weather seals.
3.4 Sustainable skins
There are issues that challenge the sustainability of TCBs, effects that must be mitigated
to preserve this building type. Some of these issues are a function of building height. The
goal of a low carbon building sector is to minimize the lifecycle impact of the building.
The facade systems are a necessary contributor to this achievement. Many of the façade
related issues are relevant to any curtainwall building.
3.4.1 Tall challenges and the lifecycle context
Lifecycle thinking is uncommon in the building industry, but critical in achieving
sustainable outcomes in the built environment. The decisions made in the planning and

61
design stages impact building performance over its full lifespan, which is many decades
in the case of tall buildings. These decisions need to be made based on considerations of
lifecycle performance. Lifecycle assessment (LCA), and lifecycle costing (LCC), are
increasingly important strategies and tools in evaluating the true impact and cost of a
material, product, building, or city.
Embodied energy
In addition to operating energy over the service life of a building, embodied energy is an
important parameter of the energy equation. Embodied energy is calculated from three
phases of building lifespan: preconstruction, operations, and end-of-life. Preconstruction
includes raw material extraction, processing and transport. Embodied energy is also
consumed in the building operations phase from repair, maintenance, retrofit and
renovation activities. Finally, the end-of-life phase included energy consumed in
deconstruction/demolition, transport, reuse, recycling and disposal. This is a
comprehensive tally including the sum of the embodied energy of all materials and
products used in a building, the energy consumed by workers commuting to and from
work during fabrication and installation, and the energy and materials consumed by
all equipment during assembly and installation activities. The total is the embodied
energy portion of a building’s energy footprint. It was long felt to be inconsequential, less
than 10 percent of energy consumed in building operations, primarily in heating and
cooling. This perception had changed significantly in recent years. Embodied carbon is
discussed in more detail in Chapter 4 (La Roche 2017; Sturgis 2017; Ibn-Mohammed et
al. 2008).
Embodied carbon emissions
The problem is not the energy itself, which could be provided from renewable sources,
but the carbon (CO2) emissions, or more accurately, the carbon equivalent emissions
(CO2e), the GHGs resulting from the burning of fossil fuels. The term embodied carbon
is the relevant consideration of embodied energy. Even more concise but less used is the
term embodied global warming potential (GWP), a measure of the relevant GHGs as
defined by the IPCC (2007), which, like carbon-equivalents, accounts for the differences
in global warming potential between the various gasses. Lifecycle assessment (LCA)
methodologies calculate the environmental impacts of both operational and embodied
energy consumed over a building’s predicted lifespan in various impact categories,
including global warming potential, nonrenewable energy consumption, human toxicity,

62
acidification, eutrophication, and others (Basbagill et al. 2013; Jolliet 2003). Just as with
looking beyond the carbon emissions resulting from operational energy consumption to
embodied energy impacts, the evolving measure of sustainability will require looking
beyond embodied energy to other embodied impacts, including embodied water,
biodiversity, toxicity and others (Richards 2015). All of these impacts are important, and
while the primary consideration here is GWP, the terms embodied carbon, embodied
GWP, embodied energy and embodied impacts, are used interchangeably.
The impact of building height includes getting the materials and workers up to the higher
elevations of a tall building, adding to embodied GWP, just as the continuous
requirement to move building occupants up and down the building adds to the operational
GWP consumption over the lifetime of the building. Unitized curtain wall technology has
developed in response to the need to minimize site labor, and is consequently effective in
minimizing energy consumption during the installation process.
Extended lifespan and, to a lesser extent, speed of construction of a system are
two factors that mitigate the impact of embodied energy. Early mid-century curtain wall
technology has evolved to the prefabricated, modular systems of today, referred to as
unitized curtain wall systems. They are designed to be factory assembled into large
modules called units (see section 4.6.4). The object is to minimize site labor, which in
many regions comes at high cost. In addition, the building site presents a host of
conditions adverse to the quality craftsmanship required for optimum facade system
performance. Factory assembly promotes quality while reducing the cost of expensive
site labor, thereby improving durability while accelerating the installation process.
Improved façade quality also reduces energy consumption from building operations over
the lifetime of the building.
Unitized curtain wall systems once installed, however, can be exceptionally difficult to
access and maintain, especially in tall building applications. Assumptions regarding
curtainwall system maintenance requirements over the service life of the curtainwall
system are usually minimal, and typically make provision only for annual cleaning
(O’Mara 2015). Even this comes at considerable expense; exterior window-washing
systems for tall buildings are sophisticated and costly. While these systems may be
effective for localized repair work, they are generally ineffective when it comes to
system-wide renovation (O’Mara 2015).

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3.4.2 The measure of sustainability
Concern with issues of sustainability in the building sector is a relatively recent
phenomenon. There was a nascent environmental movement as early as the 1960s,
spurred by such publications as Silent Spring by Rachel Carson in 1962. Limits to Growth
by Donella Meadows and her team was published in 1972; the then controversial report
commissioned by the Club of Rome brought to the forefront the problem of over-
population and resource depletion. The term sustainability, or even the term green as now
used it (along with many other commonly used terms today), were not a part of the early
environmental lexicon.
This environmental awareness bloomed through the 1960s culminating in a flurry of
activity leading up to and in the wake of the 1973 oil crisis, including important
developments ranging from passive solar design strategies to higher performing materials
and products (Wigginton 1996, 97-8; Lee et al. 2002). In fact, it was not until after the oil
crisis that insulated glazing came into widespread use, along with a growing market for
solar coatings on glass, especially the new low-emissivity thin-film coatings. Fuel
supplies and prices quickly stabilized, however, and remained inexpensive in North
America. Without the press of looming fuel shortages and high energy costs any sense of
urgency quickly dissipated, and with it the motivation for energy efficiency in the
building stock. The construction of highly glazed office buildings–with increasing
applications of residential towers–continued through the 1980s and 1990s with little
concern for energy consumption, carbon emissions, or occupant comfort. There was little
in the way of research and development in the façade industry during this period: the
domestic architecture, engineering and construction (AEC) industry was largely content
to sit the sidelines in the arena of new technology development.
The market was different in Europe, however, where high fuel costs and legislative
mandates drove innovation during this time period in the pursuit of higher performing
facade technology. Naturally ventilated double-skin systems and other innovative façade
solutions increased in frequency in Europe from the 1970s onward. These novel facades
were notable for their aesthetic as well as their functionality, but did little to inspire
similar experimentation in North America (Vaglio 2015, xxxii).
Then along with the new millennium emerged the beginnings of a sea change in the
domestic building marketplace, including the introduction of LEED–the Leadership in

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Energy and Environmental Design initiative developed by the U.S. Green Building
Council–and a rejuvenated dialog, now couched in the broader context of sustainability,
seemed to grow in parallel with a new crop of buildings certified to the new standards.
This is not to say that LEED, itself a source of controversy, was the generator of this
dialog or even that it is a uniquely effective measure of sustainability in buildings. Other
viable rating systems discussed briefly in this chapter have also emerged and are vying
for popularity with LEED. There was also growing concern over the prospect of global
warming and rapid climate change, the increasing political instability of fossil fuel supply
sources, escalating urban density, and other factors that contributed to bringing attention
to the problems posed by buildings. In 2003 Mazria, already an influential author and
spokesman for protecting the global environment, launched Architecture 2030 (2017)
focusing on the energy performance and carbon emissions of the U.S. building sector.
Regardless of cause, there was rather suddenly a surge of interest in improved
performance in buildings, and a transformation in the dialog regarding buildings and the
building skin. This dialog gradually coalesced into new concepts, developments, and
terminology, including: sustainability and sustainable development, net zero and net plus
building design, green building practices, integrative design, regenerative design,
integrated delivery methods, innovation in the building facade, emerging building codes
and standards, energy modeling, new design and analysis tools, BIM and the building
skin, façade retrofit, a plethora of new façade materials, processes and products, complex
façade geometry, the balance of daylighting and solar behavior, an ongoing debate over
large areas of glass in the building façade, and a renewed focus on performance issues
including the basic physics of heat, moisture, and sound transfer through the building
skin. The aggregation of these topics amplifies the change underway in building façade
technology, a change driven by escalating performance and aesthetic demands, often
conflicting demands, which find their nexus in the building skin.
Considerations of sustainability are integral to most, if not all, of these topics.
Sustainability within the context of the built environment is often referred to as
sustainable development, although the terms are frequently used interchangeably. The
term refers to the evolution of social and economic systems in balance with the carrying
capacity of the environment. Yet, there is no generally agreed upon definition of the term
(Strange 1997; 1999). Rogers et al. (2008, 22) in An Introduction to Sustainable
Development comments, “we experience difficulties in defining sustainable development

65
precisely or even defining it operationally.” Pezzey, a World Bank official, had compiled
some 72 definitions of sustainable development by 1997 (Rogers et al. 1997, 44), and that
number has only grown with little in the way of convergence. The term was only
gradually assimilated into common usage. In Limits to Growth: the 30-Year Update,
Meadows (2004, 295) notes the earlier use of the term equilibrium in place of
sustainability in the 1972 Limits to Growth. Most definitions of sustainability embody
more than mere survivability, pointing to the perpetuation of long term health and well-
being. Most reference origins in the 1987 Brundtland Commission report, which defined
sustainable development as that which “meets the needs of the present without
compromising the ability of future generations to meet their own needs,” thereby
establishing a baseline, but leaving much needed specificity to others. Ross et al. (1995)
finds the definition vague and imprecise. Rydin (1997) notes that the phrase is used in
varying ways depending upon context. Nonetheless, Stubbs (2004) notes common ground
with respect to term definitions is generally found in concepts that encompass “human
beings working in harmony with their natural and manmade environments to safeguard
the long term interests of the planet and its many life forms” (Rodwell, 2003) or “the
ability of an activity or development to continue in the long term without undermining
that part of the environment which sustains it” (Ross et al., 1995).
As there is no convergence on a definition of sustainability it is unsurprising that there is
also no accepted yardstick to apply when evaluating products, materials, systems, and
processes. The issue of sustainability when applied to any specific product or system
quickly becomes enormously complex, with myriad overlapping, often conflicting
considerations. “And world society is still trying to comprehend the concept of
sustainability, a term that remains ambiguous and widely abused even sixteen years after
the Brundtland Commission coined it,” comments Meadows (et al. 2004, xiv). Little has
changed, and it is arguably worse now. The marketplace has essentially hijacked the
term, which is now brimming with both products and buildings promoted as sustainable;
markets are awash in greenwash now that business and industry has discovered the value
of being recognized as environmentally responsible (BuildingGreen 2011; Graham 2016).
Humans seem possessed of a remarkable capacity to rationalize their interests to fit the
issues of sustainability, representing a significant barrier to its realization (Redclift 2005,
212-27; Kallio et al. 2007). This suggests that the biggest hurdles to sustainability may be
social rather than technical; strategies from the social sciences must be integrated with
building science in the pursuit of sustainability in the built environment.

66
3.4.3 Is green building sustainable?
A related term used to describe products, practices and buildings, intended to denote a
level of environmental responsibility, is green. The USGBC (2014a) defines green
building as the “effort to amplify the positive and mitigate the negative” impacts of the
built environment on humans and the natural environment, involving the design,
construction and operation of buildings with predominant consideration of
§ energy use
§ water use
§ indoor environmental quality
§ material selection, and
§ a building’s effects on its site.
These were used as the foundation of the LEED building rating system. But the USGBC
also recognizes the relativity of its “green” metrics. The graph in Figure 3.2 from a
USGBC (2011) white paper, nicely illustrates the relativity of the LEED rating system
relatively to sustainability. A sustainability metric of zero-impact, although that term in
itself begs definition, is shown as the bar in the graph; presumably a building that
imposes no burden on the environment or society can likely be deemed sustainable.
(Defining and measuring zero-impact is the overwhelming complexity.)

67

Figure 3.2: From USGBC policy brief (USGBC 2011).
Note the progression of the ratings over time relative to zero-impact. As a brief including
the same graph states, “Even in today’s greenest buildings, our impact is still net
negative.” Much of the use of the term, sustainability, is inappropriate, and sustainability
remains poorly understood within the building industry. It is enormously complex
conceptually, and the attempt to actually achieve it may be the greatest test of humanity.
Daly and Townsend (1996, 267) argue that sustainable development is impossible, an
oxymoron. Some question the ability of society to respond to the threat of climate change
(Smit and Pilifosova 2003; Kallio et al 2007; Adger et al. 2009; Kirstin et al. 2013).
It is important to recognize that green metrics are relative measures with respect to
sustainability. They do not equate to sustainability, or even produce sustainable
outcomes. Sustainability is often inappropriately applied as an attribute to promote
specific building products, a context in which the term green might be more appropriately
applied. The terms green and sustainable are often used interchangeably; they are not
equivalent, but there is a relationship. Green is recognized here as a more relative
measure. There are important distinctions between the terms that should reflect in their
relative usage. A specific product may be green in that it is manufactured using
renewable material and energy resources. Consider as an example the plethora of
products made from bamboo claiming green status, ranging from clothing to building
materials. Bamboo is certainly a renewable resource and an excellent material source

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from which to produce potentially green products. Excessive amounts of fossil fuels
consumed in the production of such a product, however, can easily render the production
of the product unsustainable. Or other materials used in the production of a bamboo
product, like the binders used in bamboo flooring materials, may be toxic to the
environment and produce excessive outgassing of toxic chemicals creating a health threat
in occupied spaces. Such a product cannot legitimately claim to be either green or
sustainable. As another example, a bamboo flooring product may be inexpensively
produced in China, benefiting from cheap and often exploitive labor rates that perpetuate
social inequity, then shipped across the planet to markets in America and Europe, the
transportation consuming nonrenewable fossil fuels accompanied by the resulting carbon
emissions into the atmosphere, thereby adding to the burden on the environment and
amplifying global warming potential.
The USGBC adds an important qualifier to its “amplify the positive and mitigate the
negative” position referenced above: “throughout the entire life cycle of a building.” A
product may be produced with green materials, but the pattern of its use may not be
sustainable. Lifecycle thinking is integral to sustainability (McConville and Mihelcic
2007, 937).
Similarly, a building may be measured green by codes, standards or rating systems, but
not contribute to the sustainability of the community in which it is located. A net-zero
energy building–one that produces as much energy as it consumes–may overpopulate an
area causing transportation inefficiencies resulting in excessive fuel consumption and
related carbon emissions, thereby imposing a negative impact on the sustainability of the
community. Furthermore, an appropriately sized building, not green, and with moderate
levels of energy consumption may be sustainable in a community populated with net-plus
energy buildings–buildings that produce more energy than they consume. To further
illustrate the point, a NASA-type space program is clearly not sustainable at the
community level, but may be sustainable at the level of nation or nations. Like green, the
measure of sustainability is not absolute but relative. It is, perhaps to a large extent,
contextual (Rydin 1997; Klostermann and Cramer 2006, 268-276; Kallio et al. 2007).
An important distinction between green and sustainable may be one of scale.
Sustainability is perhaps most meaningful with respect to systems at the level of
community and above: local communities, towns, small cities, major metropolitan areas,

69
regions, nations, and ultimately, the planet. Green products and practices may support the
sustainability of a system but referring to a product as sustainable, e.g., a flashlight,
seems to lack necessary context. This is reflected in popular media by articles such as
“Buying green: Products for sustainable living” (Locke 2008); a “green” flashlight may
support a sustainable lifestyle. Buildings also may be too small to be considered
sustainable independent of their context.
Green, in comparison, is applicable at smaller scale: buildings, materials, products, and
practices. Green may be regarded as an attribute that contributes to the sustainability of a
larger system. This distinction does not help much when it comes to the defining
characteristics of either term. Green may be the more appropriate term to use in a
discussion of building façade practices. The decision to use the term sustainable here
owes to a desire to frame the discussion from the onset in the broader context of
sustainability. The result is that the words are occasionally used with apparent
interchangeability.
3.4.4 The Dimensions of Sustainability
If the term green denotes attributes that contribute to sustainability, then further definition
can be found in exploring the meaning of sustainable development. Definitions of
sustainability often make reference to three fundamental spheres of consideration,
sometimes called the three pillars of sustainability: the environmental, the economic, and
the social (ECOSOC n.d.). The many definitions of sustainability often reference
environment, economy and society in some form. The Los Alamos National Laboratory,
for example, defines sustainable development as, “…developing the built environment
while considering environmental responsiveness, resource efficiency, and community
sensitivity (Farrar-Nagy et al. 2002, 2). These three basic components of sustainability
are integrated and overlapping, but provide informed vantage points from which to
consider issues of sustainability with respect to various systems.
Long before the term sustainability acquired its contemporary meaning, In Operating
Manual for Spaceship Earth, Fuller (1969) spoke and wrote at length about the problems
now covered by the sustainability umbrella. He claimed that population was not the
problem, that there existed ample resources to feed, clothe, and shelter the existing
population and many more, but that the problem was one of management. The progress
of human civilization can be seen as an evolution in the capacity to manage increasingly

70
complex systems. This evolution is still underway, and it is apparent that the deeply
complex problems presented by the issues of sustainable development pose a formidable
management challenge to contemporary sociopolitical organizations.
“What can be measured can be managed,” is a common (but contested) axiom in
industry, and this is a fundamental problem with sustainable development: what and how
to measure. Some debate whether or not it is possible to quantify sustainability (Liverman
et al. 1988; Monteith 1990; Carpenter 1993). The metrics for measuring sustainable
development are formative. Rogers (2008, 26) points out the inappropriateness of metrics
such as GDP (gross domestic product) as an indicator of sustainable economic health. As
GDP measures all goods and services, more pollution resulting in more sewage treatment
plants increases GDP, as does more crime and more prisons. He characterizes these as
defensive expenditures and suggests that these should be treated in a manner that reflects
their social, economic, and environmental cost. He emphasizes the importance of
correctly accounting for resources: resource accounting. Fuel prices, for example,
especially in the U.S., do not even attempt to account for such costs as those necessary to
protect and repair fragile ecosystems from the damage caused by extraction, nor do they
account for the research and development expenditures required to assure that renewable
energy sources are available as the non-renewables are depleted. Resource accounting
would provide the appropriate methodology to accommodate these costs. Popular
sentiment has it that the culture cannot bear the cost, especially in these challenging
economic times, not realizing that the cost is incurred regardless, it is just not measured.
Nowhere is this clearer than with budgeting practices in building construction. Most new
building and renovation projects are evaluated on a first-cost basis, meaning that a
developer will choose the cheaper of two options, regardless of the operational cost
difference (Kaisersatt 2014). Payback strategies are marginally better, with a typical
payback period of just two to five years, a timeframe that precludes the use of many high-
performance materials, products, and systems. Yet if these costs are looked at from the
broader perspective of an appropriate building life cycle, they often represent a
considerable value. Life cycle cost analysis (LCCA) is a method for evaluating whole-life
building cost, from acquisition through disposal (Fuller 2016). LCCA accommodates
comparative assessment between products, systems and design variations in the context
of both initial and operating costs of full building lifespan.

71
The issue of measurement is partially one of time and scope. Sustainability is about the
consideration of a longer timeframe. There is no long-term view to GDP. Sustainable
development, in contrast, ultimately measures time in ongoing human generations. Issues
are examined within the context of service life or lifecycle. This, too, can be a challenge.
There is no generally agreed baseline for the design service life of a tall building. More
concerning, the question is only really asked. Most tall buildings are designed and
constructed with no clear definition of life expectancy. This is discussed in section
4.3.11.
Data collection and the development of appropriate metrics for evaluating sustainability
is critical, but ultimately, many things do not easily lend themselves to measurement. A
successful enterprise learns that what cannot be measured still must be managed.
3.4.5 Environmental Protection
Most people equate sustainability with the environment (Simpson and Radford 2012).
Economic and social development must be balanced with environmental protection.
Buildings consume resources in the form of energy, materials, and water, and generate
waste and emissions, through their entire lifecycle, from construction through their
service life, dismantling, and disposal, thereby producing a significant impact on the
environment. Green practices involve mitigating these impacts in a manner to support
system sustainability through such strategies as conservation, reuse, recycling, optimizing
efficiency and durability, material use, and resource management.
3.4.6 Economic Development
The three pillars of sustainability are also referred to as the triple bottom line, making
reference to accounting practices that must balance the three components in each
analysis. Economic considerations of sustainability include the equitable distribution of
wealth, the mitigation of poverty, and economic management that provides for the
feeding, clothing, sheltering, education, and health care of a population. At the building
level, these considerations involve balancing the environmental and social attributes of
sustainability with affordability, which is certainly cross-linked with such aforementioned
environmental considerations as conservation and the optimization of such measures as
energy performance. Building economic considerations involve cost-benefit analysis over
a full building lifecycle of appropriate duration.

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3.4.7 Social Factors
Sustainability has a social dimension that is as important as the environmental and
economic considerations that tend to dominate the dialog on sustainable issues. No
building stands alone. Buildings dominate the built environment that is shaped by, and in
turn shapes, culture. Green buildings are an integral part of the larger fabric of sustainable
development and the evolution of sustainable communities. Affordable housing and
office space is a growing problem in many communities, and a fundamental aspect of a
sustainable community. Manhattan is rapidly becoming an island of the rich (Roberts
2014). Packed trains flood the borough every morning as workers that cannot afford to
live locally commute from distant suburbs (Clarke 2015). The result is a loss of diversity
in the local population, a diversity that provides both cultural vitality and efficiency to a
community (Sorkin 2013).
The effort to create green buildings should not be allowed to compromise community
sustainability by reducing the availability of affordable housing and office space. As
noted earlier, one of the motivations for facade renovation of existing office buildings is
to raise the real estate classification, with the goal of higher lease and lower occupancy
rates. Similarly, the renovation of older residential properties, or commercial conversions
to residential properties, intend to upgrade the building image and amenities, including
“greening” programs and LEED certification. LEED certification means little to the
person that can no longer afford to live in the building, or the small business that can no
longer afford to lease space in a green retrofit office building.
While the social dimension of sustainability could easily be regarded as outside the scope
of this investigation, it would run counter to sustainable thinking to disregard these
considerations entirely, especially since the thesis involves sustainable practice.
Sustainability issues are inherently complex, as they are necessarily holistic and tightly
woven with the many threads of environmental, economic, and social considerations. It
must be acknowledged that the greenest of buildings, whether new or retrofit, can be
rendered fundamentally unsustainable in the larger context of community and sustainable
development.
3.4.8 Sustainability and the building skin
Façade practices are challenged by the overlapping performance considerations and
functions that converge at the façade system. Sustainability starts with fundamental

73
performance requirements of buildings science and human comfort. Figure 3.3 diagrams
some of these considerations. Many of these can end up as competing considerations, for
example, the provision of daylight and the controls of glare, or the provision of
ventilation and the control of air infiltration. The functions and attributes interact in
complex ways, and must be considered as an integrated whole; addressing them in
isolation or as a limited group will often produce unexpected and unwelcome results.
Façade system design confronts the challenge of balancing these myriad considerations
with available products and design strategies (Herzog et al. 2004, 8-52; Straube and
Burnett 2005, 36-39).

Figure 3.3: The building façade is the nexus of many, often competing, considerations that ultimately
determine façade, and much of building, performance.

74

Figure 3.4 suggests the many layers of façade functionality and strategies that must be
balanced to sustainably achieve the ultimate goal of most buildings; the provision of
inhabitant health, comfort and productivity. The progressive development of façade
solutions that support sustainable outcomes involves peeling back these layers while
constantly evaluating appropriate performance metrics as the design develops. The
ordering of the layers varies by project, and must be considered on a case-by-case basis.

Figure 3.4: Façade strategies and performance considerations as layered attributes toward the goal
of health, comfort and productivity.
occupant health
and comfort
sensors/controllers for dimmable lighting
protected cavity buffer
operable shades and windows for natural ventilation
daylighting zone

glare control
dynamic shading system
static shading system with optimized solar orientation
second layer of facade - double skin system
building integrated photovoltaics
building integrated wind harvesting systems

building integrated greywater collection
resilience

operations and maintenance

durability
whole building energy modeling

systems integration
life-cycle assessment

embodied energy
disassembly and recycling

end-of-life impacts

primary glazing: weather barrier
safety and security
thermal and acoustic insulation

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3.4.9 Façade functions and the façade affect zone
Primary facade functions and their performance contributions developed over years of
project experience are included in Table 3.1. The building skin impacts both the
performance and appearance of buildings in a unique and compelling manner quite unlike
any other building system. The role of the façade in building energy performance is
fundamental. It is often second only to overall building form as an architectural
consideration in many building programs. The conditions of use may amplify building
energy consumption—as with plug loads in office buildings and equipment loads in data
centers and hospitals—adding to the energy burden, but the building skin contributes
significantly to the baseline efficiency of a building. The building skin is a primary
building system that acts as arbiter presiding over the boundary between inside and out,
mediating between opposing requirements such as the provision of daylight and view and
the need for thermal insulation, and moderating mass and energy exchange between
inside and out, as with the provision of daylight without glare or excessive solar gain.
The façade, therefore, plays a dominant role in providing comfort to the building
occupants (Browning et al. 2012). It simultaneously plays a defining role in the
appearance of a building and, thereby, as an expression of culture, contributes to the
character of the built environment.

76
Table 3.1: Façade functions and performance contributions
Function Description Contribution
Structural the skin must hold itself together and to the building
superstructure, accommodate all building movements under
various loading conditions, and transfer exterior loads (wind) to
the building superstructure
life-safety
durability
Thermal regulate heat transfer between inside and out energy efficiency
health, comfort, and
productivity
Solar control solar heat gain and glare energy efficiency
health, comfort, and
productivity
Acoustical moderate the transfer of sound between inside and out health, comfort and
productivity
Moisture regulate the transfer of moisture between inside and out durability
health, comfort, and
productivity
Air regulate the transfer of air between inside and out, providing
natural ventilation as required and preventing unwanted air
infiltration
energy efficiency
health, comfort, and
productivity
Daylight provide and moderate daylight from the exterior to the interior,
controlling glare and solar gain
energy efficiency
health, comfort, and
productivity
View provide view to the outdoors and connection to the outside
environment
health, comfort, and
productivity
Security and
safety
provision of blast, ballistic, and forced egress; missile impact
resistance, as appropriate
life-safety
Energy thermal and electrical energy harvesting and distribution
through solar thermal and façade-integrated photovoltaics
onsite energy production
Communication façade integrated signage and digital displays messaging,
communication and
advertising
Branding linking and expressing corporate or institutional values through
building appearance
building brand value
Beauty the building skin plays an integral role in the aesthetic
expression of the building
durability

Straube and Burnett (2005, 36-39) break down facade functions in some detail, charting
specific loadings against functional categories, even addressing professional
responsibility, revealing the cross-disciplinary considerations presented by the building
skin.

77
3.4.10 Operational energy in the façade zone
The U.S. Energy Information Administration tracks building energy end use in the
Commercial Buildings Energy Consumption Survey database (CBECS 2015). The façade
affects 4 of the 11 end use categories responsible for over 50% of energy consumption
(Figure 3.5).

Figure 3.5: Energy end use data indicating areas typically affected by the performance of the
building skin. These areas are responsible for more than 50% of energy consumption (adapted from
DOE 2012, chapter 1-2).
The façade has a strong influence on heating and cooling loads, and can play a role in
natural ventilation by incorporating operable windows and vents. Daylighting can
effectively reduce electrical lighting loads and the cooling loads incidental to indoor
artificial lighting. Building envelope transparency in combination with thermal mass can
contribute to passive heating and cooling strategies.
With urban populations in 2016 at over 80 percent in North America and most of Europe,
nearing 60 percent in China and growing rapidly worldwide (World Bank 2017), and
with people spending 90 percent of their time indoors (EPA 2017), the performance of
the building façade is taking on ever greater importance.

78

3.4.11 Sustainability is a Design Problem: Strategies to enhance
façade performance
Figure 3.6 represents façade zone design strategies drawn from the above considerations
that support sustainable outcomes. These include primary categories of glazing options,
renewable supply/storage PV and thermal, daylighting and shading, framing,
configuration (e.g., double-skin), insulation, energy recovery façade ventilation,
integration and automation. In addition, new system designs should accommodate future
retrofitting, and consider cassette and overcladding system integration.

79

Figure 3.6: A sampling of design strategies and considerations in the façade zone (courtesy of
Advanced Technology Studio-Enclos).
3.5 The Strands of Façade Sustainability
While a comprehensive widely accepted definition of sustainability remains elusive,
researchers across a broad spectrum of disciplines continue to struggle with the definition
of benchmarks and metrics for key sustainable attributes (Robért 2000, 243-54; Curzons
et al. 2001, 1-6; Ostrom 2009, 419-22). This is true at all scales of sustainability research.
At the planetary scale, for example, Table 3.2 represents nine planetary boundaries
proposed by scientists as a key metric set that, if the activities of humanity do not stray
beyond these boundaries for any extended time, may indicate favorable conditions for the
continuation of human enterprise (Rockström 2009). The values are preliminary,

80
however—some thresholds are unknown or uncertain, some datasets are incomplete, in
some cases systems behavior is incompletely understood—and much work remains
before their accuracy can be validated. Evidence suggests that three of the boundaries
have already been exceeded. There is inadequate knowledge to even establish preliminary
values for two of the boundaries.

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Table 3.2: Proposed planetary boundaries. Derived from Rockström et al. (2009, 8-9) and Folke (2013,
22-24).

The point is the uncertainty and ambiguity that exists at all scales of sustainability
research, and all levels of the sustainability dialog; it is little wonder the dialog is
dominated by sustainababble (Engelman 2013). The deeper one drills down through the
layers from planet to nation, region city, community, building, building system, product,
THE NINE PLANETARY BOUNDARIES
EARTH SYSTEM
PROCESS CONTROL VARIABLE
PROPOSED
BOUNDARY
CURRENT
STATUS STATE OF KNOWLEDGE
climate change co2 concentration ppm
350 387
• ample scientific evidence
• multiple sub-system thresholds
• debate on position of boundary
biodiversity loss extinction rate
species/million/year
10 >100
• Incomplete knowledge on the role
of biodiversity for ecosystem func-
tioning across scales
• thresholds likely at local and
regional scales
• boundary position highly uncertain.
nitrogen cycle N2 removed from atmo-
sphere for human use
millions of tons/year
35 121
• some ecosystem responses known
• acts as a slow variable, existence
of global thresholds unknown
• boundary position highly uncertain
phosphorus cycle P flowing into oceans
millions of tons/year
11 8.5–9.5
• limited knowledge on ecosystem
responses
• high probability of threshold but
timing is very uncertain
• boundary position highly uncertain.
ozone depletion concentration
(Dobson unit)
276 283
• ample scientific evidence
• threshold well established
• boundary position implicitly agreed
and respected
ocean acidification mean saturation state
aragonite in surface
seawater
2.75 2.90
• geophysical processes well known
• threshold likely
• boundary position uncertain due to
unclear ecosystem response
freshwater use human consumption
km3/year
4,000 2,600
• scientific evidence of ecosystem
response but incomplete and
fragmented.
• slow variable, regional or subsys-
tem thresholds exist
• proposed boundary value is a glob-
al aggregate, spatial distribution
determines regional thresholds
land use percentage of land con-
verted to cropland
15 11.7
• ample evidence of impacts of
land-cover change on ecosystems,
largely local and regional
• slow variable, global threshold un-
likely but regional thresholds likely
• boundary is a global aggregate
high uncertainty, regional distribu-
tion of land-system change critical
atmospheric aerosol
loading
atmospheric particulate
concentration by region to be determined
• ample scientific evidence
• global threshold behavior unknown
• unable to suggest boundary yet
chemical pollution i.e.; concentrations in
environment of persistent
organic pollutants,
plastics, heavy metals,
nuclear waste, etc.
to be determined
• ample scientific evidence on
individual chemicals but lacks an
aggregate, global-level analysis.
• slow variable, large-scale thresh-
olds unknown
• unable to suggest boundary yet

82
and material, the dialog becomes increasingly muddled and the claims increasingly
meritless. There are good reasons to question the relevance of sustainability at the finer-
grain scales of building and below. Still, buildings, building systems, building products
and materials are ultimately part of the whole-system, and thereby contribute to, or
detract from, sustainability at the higher system levels.
The intent is not to provide yet another definition of sustainability, nor to propose a
general framework for the evaluation of sustainability. The strategy is to develop a set of
sustainability attributes relevant to the TCBs and their façade systems; the “strands of
façade sustainability” (Figure 3.7). Stranded cable is the metaphor for this interrelated
and interacting set of sustainability considerations. The attribute set is included in the
following section, with each attribute briefly discussed. The attributes selected for further
investigation are embodied carbon, durability, adaptability and resilience.

83

Figure 3.7: An interrelated and interdependent set of sustainability considerations developed for the
assessment of façade design and delivery practices in TCB applications.
3.5.1 Façade Sustainability Attributes
The problem of evaluating the sustainability of facade retrofit practices in curtainwall
buildings is the identification of appropriate for conducting the evaluation. The definition
of a foundational set of sustainability considerations is developed following, as
candidates to test the hypothesis regarding façade practices on TCBs.
Key considerations analyzed in a context of appropriate scope and scale hold the
potential to inform an evaluation of the extent to which a system supports sustainability,
in this case, the extent to which curtainwall technology in tall building applications
supports sustainability in the built environment. The remainder of this chapter identifies

84
and explores a set of sustainability considerations generally relevant to buildings and
building systems, but intended for the narrower focus of TCB façade systems.
The sustainability attributes derived from this study are summarized in Table 3.3, with
arguments presented for each attribute in the following sections.

85
Table 3.3: Primary and secondary façade zone sustainability attributes must be integrated in
balanced response as part of holistic building design process, considered over building lifecycle.
PRIMARY
CONSIDERATIONS SECONDARY STRATEGIES/TOOLS/PROCESSES
C&D waste reuse reuse is optimal strategy; design for reuse
down-cycle asphalt/concrete/other filler material
recycle aluminum; glass can be but is not recycled
disposal landfill
durability material
degradation
material selection: durable materials
adaptability design for adaptive capacity
repairability design for repair of function-critical materials, components
maintainability service life plan (SLP) and maintenance plan
upgradability design to accommodate retrofit
obsolescence design for adaptive capacity
economy cost first cost budgeting
value engineering
real-time budgeting during design development
use collaborative delivery strategy, e.g., design-assist
don’t skimp on design phase
lifecycle costing (LCCA)
energy & carbon operational balance WWR, insulation, daylighting, thermal
see Figure 3.6
embodied material selection; service life extension; less is more
IEQ comfort integrate biophilic design principles
daylight/glare daylight design; glare analysis
view from each workstation
ventilation provide maximum natural ventilation
integration whole building building management system (BMS)
building systems BMS
façade system integrated system needed
resilience shocks & stresses robustness and redundancy
see Table 6.3
water potable conservation
grey water harvesting
filtration and purification

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3.5.2 Construction and demolition C&D waste
Not only is the building sector a leading energy consumer and emissions producer, it is
also a leading contributor to the solid waste stream. With thousands of landfills in North
America alone, this is an increasing environmental concern. The problem with waste in
the modern world is a reflection of the values of a consumer throw-away culture. This
problem does not stop at buildings. Little consideration is given to durability in new
building design or in the major systems and products that comprise them.
The EPA (2017a) defines C&D materials as debris resulting from the construction,
renovation and demolition of buildings and infrastructure. Among the materials listed,
those most relevant to the façade system include: metals, glass, windows, doors and
concrete. The EPA encourages reducing, reusing, recycling and rebuying as strategies for
C&D reduction, and points to benefits including:
§ boost employment in recycling industry (230,000 jobs in 2016)
§ reduce project costs including purchase, disposal, and transport
§ reduced burden on landfills and related environmental issues
§ offset impact of resource extraction and consumption from virgin material use
At 534 million tons in 2014, C&D debris was more than twice municipal solid waste,
with demolition accounting for 90 percent of total C&D debris.
Cabeza et al. (2013) note the importance selecting materials with “high recycling
potential” to mitigate the impacts of energy and resource use over time. McDonough and
Braungart (2002) in Cradle to Cradle: Remaking the Way We Make Things, present a
compelling case for the vital importance of recycling, using a systems model to represent
a materials universe of biological and technical nutrients. Materials and chemicals toxic
to human and environmental health are excluded from the body of technical nutrients
with the objective of eliminating their use entirely. Rather than a linear product lifespan
of extraction, fabrication, use, disassembly, and disposal, the goal is a closed loop in
which technical nutrients are recycled and biological nutrients are composted. They use
the terms upcycling and downcycling to differentiate significant differences in recycling
processes. Materials are downcycled into lesser materials in progressive steps, ultimately
becoming waste. Recycled materials can be used over and again with no loss of value.

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Upcycling is a value-added process in the truest sense of the term, in which lesser
materials are upgraded during the recycling process.
Automotive glass provides a useful example. (Float glass use is dominated by buildings,
with automotive use as second.) These glass products, used as automobile windshields
and windows, are highly engineered materials involving extensive secondary processing
to the raw float glass: bending, heat treating, laminating, special interlayers with heating
elements, special tints, and the application of special coatings. The average lifespan of an
automobile in the U.S. is over 11 years (USDoT 2016). If an automobile is involved in an
accident and permanently disabled, undamaged glass may be reused in identical
automobiles to replace damaged windshields or windows. Reuse, as a form of recycling,
is typically the most efficient form of recycling, requiring the least amount of energy in
adding to the service life of a product.
Alternately, the glass panels could be removed from the disabled vehicle and reprocessed
in a recycling operation. If simple automotive glass is added back to the raw material
inputs into the float glass process, a practice that is known to reduce the energy required
to produce raw float glass, the material is recycled. Glass is infinitely recyclable with no
loss of quality. If, on the other hand, the recycled material is used to produce a specialty
glass, such as a low-iron glass, the material has been upcycled. Glass materials are
sometimes machine ground to small pieces and used as fill material for asphalt or
concrete, a practice commonly referred to as recycling while being in actuality a prime
example of downcycling.
In practice, automotive glass is typically not recycled. The sound of breaking glass
accompanies the familiar scene of an end-of-life automobile carcass being compressed
into a block of material; the windshields and windows are one of the few components not
stripped from the frame for some form of recycling. The compressed blocks of material,
predominantly metallic in nature, are then fed into a shredder that produces fist-sized
hunks of mixed materials. The ferrous and nonferrous materials are then extracted for
recycling. Roughly 20% of the material remains after this process and is called
automobile shredder residue with (ASR), which is considered waste and commonly
landfilled (Guatney and Trezek 2012). Thus, the technical nutrients embodied in
automobile glass products are lost.

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There are subtleties to these recycling processes and practices. Even if a rear window of
an SUV, for example, with holes for hinges and wiper, heat treated, laminated with an
interlayer containing heating wires, coating to reduce glare and solar gain, is reclaimed
and processed as required for reintroduction into the float glass manufacturing process,
the totality of these secondary processes has been lost. This practice would, then,
represent a form of down-cycling. Eventually, science and the recycling of materials must
become a sophisticated science. McDonough and Braungart (2002) predicted that
landfills will one day be mined for their techno-nutrients, a notion that is rapidly gaining
market traction (Mission 2016; Kelland 2008).
The goal or requirement for any green practice should be to use as many used or recycled
materials as possible, and to only use materials that are themselves reusable and
recyclable. Progress toward a sustainable future will ultimately require legislation
mandating the use of recyclable materials and products; if it cannot be recycled, it cannot
be marketed. The process and technology of recycling will then evolve to the required
level of sophistication.
This is the aim of the circular economy, as promoted by the Ellen MacArthur Foundation
(2017) as an antidote to the mass consumer culture. The circular economy is conceived as
a closed-loop system, “restorative and regenerative by design.” The intent is to maintain
“products, components and materials at their highest utility and value at all times.” The
notion of a façade system designed to facilitate repair, maintenance, retrofit and
renovation on a perpetual basis, as discussed in Chapter 4, is consistent with the concept
of the circular economy.
There are three possible solutions to the problem of recycling/reusing architectural glass:
1. The glass industry can develop the techniques and infrastructure required to
recycle post-consumer architectural glass.
2. Building glass can be reused as part of a façade renovation. For example, in the
2010 renovation of the Empire State Building, the onsite renovation of the
insulated glass units used in the windows accommodated the reuse of the float
glass material.
3. Finally, the float glass can conceivable be used in a way that would facilitate
recycling, including the elimination of surface coatings on the glass, and bonding
of the glass to other window components.

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This still leaves the logistical problem of collection and transport to a float glass
manufacturer, but this is not a technical problem.
3.5.3 Durability
Durability is the focus of Chapter 4 and critical to the arguments being made.
Enhanced durability minimizes environmental impacts through resource management;
using fewer resources and minimizing construction waste. Maintenance, adaptability, and
the concept of service life are strongly linked to durability, so are briefly discussed here.
Durability is not an innate property of a material, but rather the result of matching
physical attributes of a material with the conditions of its application (Kesek 2002;
Athena Institute 2006). A material may be long lasting in one application but fail rapidly
in another as a function of use and exposure. Certain dissimilar metals, for example, may
be used in in a connection detail, and in a consistently dry environment may pose no
problem. If exposed regularly to moisture, however, the materials may corrode rapidly.
Durability may be regarded as a quality combining several important aspects of
performance. Nicastro (1997, 101) defines durability as, “the quality of maintaining
satisfactory aesthetic, economic, and functional performance for the useful life of a
system.”
Facade systems are part of the building envelope, and as such mediate between the
building interior and natural climate. The materials, products, and assemblies that make
up the facade systems are exposed to the weather. Weathering is a term used to describe
the effects of exposure to weather, which Nicastro (1997, 94) lists as ultraviolet radiation,
temperature, moisture, wind, ozone, carbon dioxide, pollution, and freeze-thaw. these
effects tend to degrade materials and assemblies over time. This is what most think of
when considering durability. It turns out, however, that degradation is not the leading
cause of building demolition. Other forms of obsolescence play a leading role, and these
must be included as durability considerations (Section 4.3.6).
Service Life
A defined design service life is seldom established for buildings, even large building
projects represented as green (section 4.3.11). The same is true of their major systems.
Curtainwall systems are routinely designed with no consideration given to need for future
repair, maintenance, retrofit or renovation. The necessity of upgrade or replacement is

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predictable, and system designs should anticipate and accommodate this requirement.
The service life of a system is determined by its weakest link. The concept of differential
durability (section 4.3.5) addresses this as a system design problem. The components that
comprise the curtainwall system embody varying lifespan potentials. The insulated glass
units (IGUs) and seals are determined to be the weak links in contemporary curtainwall
systems (section 4.4.7). Yet no consideration is given to accommodating the change-out
of these glass panels, or the inspection, maintenance, replacement of the seals, in the
design of the curtainwall systems. This restricts options for their retrofit, resulting in
replacement as the leading façade retrofit strategy, a process both expensive and
disruptive to ongoing building operations, and one that may prompt consideration of
building replacement as an alternative, resulting in the loss of the entire building.
The specification of a design service life for a building is fundamental to any building
program—especially to any program that describes itself as green—and that the various
systems that comprise the building should be similarly specified with a design service life
that is in synchronicity with that of the building.
Maintenance
Maintenance is a planned program of treatment of materials and systems in a manner to
preserve their intended function, a consideration integral to durability. This includes both
considerations of performance and appearance, depending upon the item. Few materials
are maintenance-free over their potential service life, and many products and systems are
supplied with prescribed maintenance requirements as conditions of warranty and service
life. Maintenance planning varies considerably between building projects, at least
partially as a function of building and owner type. A speculative developer of office
buildings will often have little regard for either durability or maintenance considerations
(O’Mara 2014). An owner-occupied building project typically elevates these issues. The
design of institutional buildings is often driven by considerations of durability and
maintenance requirements (GSA 2005; 2012).
High labor costs motivate owners to press for long lived materials and systems that
require minimal maintenance. Double-skin facades, for example, are generally
accompanied by additional maintenance considerations involving cleaning of the glass
inside the cavity of the double skin wall, which may involve operable access panels,
catwalks and rigging within the cavity, and even the sealing and pressurization of the

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cavity to accommodate or reduce maintenance requirements. Automated shading systems
within the cavity require access and maintenance. The ongoing maintenance costs offset
energy cost savings provided by the wall system.
Service life planning (SLP) is a process that accounts for the repair, maintenance,
upgrading, and renovation of buildings and their major systems (section 4.3.12), and an
integral component of green building practice. The design service life establishes the
goal, the SLP defines the strategy to realize that goal. Green practice requires the
consideration of comprehensive maintenance requirements for every material, product,
and system, and the specification of these requirements as part of ongoing building
operations. Repair, maintenance, retrofit and renovation activities produce recurring
embodied carbon impacts through a building’s operational cycle, as discussed in the
following energy and carbon section. Minimizing and facilitating maintenance activities
for optimal efficiency over a building’s lifespan is an important component of SLP.
Adaptability
The degree to which a material, product, or system lends itself to reconfiguration and
reuse is a measure of adaptability. The application of this process is adaptive reuse.
Buildings, for example, can be converted from one use to another; an old industrial loft
building can be converted to residential units. They should support the expansion,
contraction and evolution of function over time. Buildings are not typically designed in
anticipation of future adaptive reuse. Some variation of functional obsolescence is the
leading cause of building renovation and replacement. Adaptive capacity is a primary
design strategy to mitigate the threat of functional obsolescence (section 4.3.7).
There is wide variation in adaptability as a material attribute, and as a general pattern the
more a material is processed the less its adaptability to reuse. The raw materials of float
glass: silica, soda, and lime, are fit for any appropriate process. When combined in the
float process they form the flat, transparent glass material ubiquitous to the built
environment. Raw float glass, if handled carefully, can be removed from a window
application, recut as necessary, and applied to a new window application, where it will
last indefinitely until broken or reused again. To prevent breakage, or to modify the break
behavior of glass, it is heat-treated as a secondary process. Glass can no longer be cut
once heat-treated, preventing the glass from being resized for a new application. The

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reuse of heat-treated glass requires that the new application accommodate the existing
dimensional properties of the glass, limiting conditions of reuse.
In general, however, and similar to durability, adaptability is less an inherent material
property than the result of initial design and planning that anticipates future conditions of
reuse. A small investment in the early design phase of a project can produce significant
downstream benefits in the ecological footprint of a material, product, or system, and
ultimately, of the built environment.
3.5.4 Economy
Economy is one of the three pillars of sustainability (WCED 1987). The economy
represents perhaps the greatest challenge to and opportunity for the realization of
sustainable societies. Daly (1993, 267-74) argues that sustainable development is an
economic impossibility. Economic factors are integral to any consideration of
sustainability.
TCB façade systems are expensive. Curtainwall systems in low to mid-rise applications
typically ranging from 17-22 percent of a building’s total construction cost (Cheung and
Farnetani 2017, 35; Arnold 2016), and with state-of-the-art high-performance systems in
tall and supertall building applications can run to 25 percent and higher (O’Mara 2015).
Future façade retrofits are also expensive, given that they most often involve complete
removal and replacement of the façade system. With the disassembly and removal costs,
combined with the expensive logistics involved in a façade retrofit required to mitigate
disruption to ongoing building operations, a façade replacement type retrofit will
generally cost more on a unit basis than a curtainwall installation on a new building of
similar type.
There is a widespread absence of lifecycle thinking in the building industry, and the
predominance of first-cost considerations dominate planning and design decisions. The
result is an environment unconducive to alternatives that enhance sustainability but are
accompanied by an incremental cost. Economic considerations are discussed throughout
this narrative, but are not one of the primary attributes of sustainability investigated, and
the opportunity is taken to examine potential solutions largely independent of economic
considerations.

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The building stock is a primary cultural asset, a dominant component of national
infrastructure that requires protection in the form of maintenance and renewal. Even in
the current strong economy, key infrastructure in the U.S. is being neglected, including
buildings that need renovation. The risk in delaying mitigating actions is the potential for
future economic downturn that could effectively prevent resolution, burdening societies
with obsolete buildings that fail to provide their intended function, and do not provide a
level of service quality that supports comfort, health and productivity.
3.5.5 Energy and carbon
The energy consumed during the operations phase of a building’s lifespan dominates the
building performance and sustainability dialog. This is appropriate, as the burning of
nonrenewable fossil fuels is the source of the biggest problem issuing from the building
sector: carbon equivalent emissions, CO2e. The problem is not in the energy
consumption itself; the energy from renewable sources like solar, wind or hydro produce
are responsible for minimal carbon emissions, primarily relating to equipment
manufacturing required to support these energy-generating processes.
Carbon emissions refer to CO2e produced during a building’s operational cycle for
purposes of heating, cooling, ventilation, and other operational functions. Embodied
carbon emissions are CO2e produced during all four phases of building lifecycle:
1. preconstruction—ranging from material extraction through cycles of
manufacturing, including all extended transportation, and delivery to jobsite.
2. construction—all construction activity including worker transport to and from
jobsite, equipment operation, installation activities until the date of occupancy.
3. operations—emissions produced during a building’s operational cycle from
repair, maintenance, retrofit and renovation activities are classified as recurring
embodied carbon impacts.
4. termination—end-of-life emissions produced by disassembly, demolition, reuse,
recycling, or disposal, including all related transportation.
Embodied carbon is also a focus of this research because of its relationship to
maintenance and durability, discussed previously.
Owing to the carbon emissions produced through the consumption of fossil fuels,
buildings are the predominant contributor to climate change, as discussed in Chapter 1.

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The problem with carbon
Greenhouse gas increases since the onset of the industrial revolution in the mid 18th
century is mainly attributable to human activity and are directly linked to increased
global temperatures (IPCC 2014a). The IPCC defines climate forcing as, “An externally
imposed perturbation in the radiative energy budget of the Earth climate system, e.g.
through changes in solar radiation, changes in the Earth albedo, or changes in
atmospheric gases and aerosol particles.” The National Oceanic & Atmospheric
Administration (NOAA) maintains the Annual Greenhouse Gas Index (AGGI), which
tracks climate forcing of all long-lived well-mixed greenhouse gassed, primarily carbon
dioxide (CO2), methane (CH4), nitrous oxide (N2O), and halogenated compounds
(mainly CFCs) (Butler and Montzka 2017). The index excludes sources of warming that
are at all controversial in nature and limits inclusion to only the well documented “long-
lived, well-mixed” gasses.
The index includes measures of these gasses in the atmosphere as particulate in parts per
million (ppm). Pre-industrial levels hovered around 300 ppm or less. Levels climbed
through the industrial age, and have now topped 400 ppm. Moreover, the rate of increase
in emissions has been growing, and has recently exceeded 2ppm/year. The current global
monthly mean level as of June 2017 is 405.91 ppm, up 2.55 ppm from data recorded one
year previous. Figure 3.8 shows the trend over the past 5 years (NOAA 2017).

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Target limits ranging from 350 to 450 ppm have been debated and adopted by various
organizations. McKibben, an author and climate change activist who founded 350.org
argues to reset the target level at 350ppm, a level surpassed around 1988. Regardless,
there is general agreement among the scientific community that carbon emissions
represent a significant potential threat, that they are producing warming as the result of
human enterprise, and that efforts must be made to at least slow their growth.
Commercial buildings present a significant opportunity to reduce carbon emissions
because of the high fossil fuel consumption that characterizes this sector. Yet in spite of
stepped up efforts by the building community starting around the turn of the new
millennium, the annual growth of the AGGI is accelerating. Much more must be done.
Embodied Carbon
Malin (2008) notes that a building carbon footprint is generally equated to fossil fuel
energy consumption from building operations, but also includes secondary emission
sources like those resulting from building construction and transportation to and from the
building. As buildings become more efficient operationally, these secondary emission
Figure 3.8: 5-year trend in monthly mean CO2 (NOAA 2017).

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sources become more significant. This is referred to as embodied energy, or with
reference to the emissions produced, embodied carbon. Products, materials, and the
processes they embody play a significant role in sustainable buildings and construction
practices. An installed building product represents the energy required to produce,
transport and install that product, along with the emissions that accompany these
processes. Mazria comments, “Consider this: the first day a building is occupied, all of
the carbon emissions from that building come from building products and the building
process.” (Mazria 2011a) As Mazria suggests, a newly completed building starts its
operational lifecycle with a significant energy debt. Architecture 2030 has launched the
2030 challenge for products with the aim of embodied carbon reductions of 50 percent by
2030. Beyond the energy/emissions cost to produce the product, analysis must include the
full lifespan processes of raw material extraction and processing, production and
assembly cycles, transport, installation, removal, and disposal, recycling, or reuse.
The ratio between embodied energy and the energy consumed in operations over the life
of a building increases as buildings become more energy efficient. High-performance
buildings often have a much higher ratio than conventional buildings. As buildings move
toward zero-carbon operations, the embodied carbon becomes increasingly predominant.
Embodied impacts were long dismissed as being less than 10 percent of lifecycle
emissions, but recent research has indicated that embodied carbon can represent a much
higher percentage of lifecycle impacts (section 4.3.3).
3.5.6 Heritage value of TCBs
The heritage value of CTWBs is the focus of Chapter 9.
In the U.S., the National Trust for Historic Preservation (NTHP) is charged with the
protection of buildings and places of recognized cultural significance. This is an aspect of
the 3rd pillar of sustainability (Figure 3.1), culture, but the linkages between these pillars
are strong, in this case with relevance to economic and environmental value in addition to
cultural value.
Stubbs (2004) notes the abundance of preservation literature attributing heritage value to
environmental, social and economic considerations. The conservation of buildings has
multiple values:

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1. Reuse as a sustainable option to building replacement, providing environmental
value. The reuse of buildings minimizes environmental impacts in comparison
with new construction in nearly all instances (Frey et al. 2011).
2. The preservation of culturally significant buildings and places as a strategy to
preserve cultural identity and constructive cultural evolution (Rodwell 2003). This
defines the linkage between sustainability and conservation, establishing them as
complimentary considerations (Stubbs (2004). There is much disagreement and
debate, however, about what constitutes heritage value, as well as its relative
importance (Larkham 1966; Cohen 2001). Sustainability indicators seldom
reference heritage considerations, being dominated by more tangible metrics of
GHG emissions and land use statistics.
3. The notion of heritage buildings as capital assets of economic value. Economist
David Throsby (1999) recognizes cultural phenomena like heritage buildings as
capital assets, and argues for their formal recognition as cultural capital, a new
and unique form of capital as differentiated from physical, human and natural
capital.
20th century heritage and TCBs
Tall curtainwall buildings, a building form that emerged in the early 20th century with
the work of the early Modernists, are gradually being recognized for their heritage value.
Individual buildings are undergoing sensitive and expensive restorations and renovations,
Lever House and the U.N. Secretariat Building among them. While these iconic examples
of the postwar Modernist period are prime candidates for preservation, many others are
languishing in an advanced state of deterioration, in need of potentially unaffordable
renovation, and potentially subject to demolition and replacement.
TCBs, however, are also being recognized for their heritage contribution to urban habitat,
especially in unique areas like Midtown Manhattan, densely populated with this building
form (Jerome 2014). Ayón and Rappaport (2014) point to over 200 building from this
period that they characterize as modern vernacular. They claim these buildings possess an
aesthetic and cultural value, that they can and should be returned to class-A office
building standing with energy retrofits including façade system upgrades.
Preservation and sustainability may be complimentary concepts, but it can be an uneasy
linkage. While there is growing appreciation for the artifacts of Modernism, including
TCBs, there is a clear conflict with headline sustainability metrics. The early curtainwall
systems were never good energy performers or comfort providers, even when compared

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with the masonry building practices of the time (Oldfield et al. 2009). Balancing
sustainability and preservation goals in this context presents a distinct challenge. In
addition, major façade renovations in the form of overclad and façade replacement are a
clear threat to preservation aims. Even repairing these old curtainwall systems is
challenging and changes the appearance of the original façade system (Jerome and Ayón
2014, 18). The lack of options resulting from the general failure of these systems to
anticipate in any way the need for future retrofit drastically reduces the renovation
options, resulting in façade replacement as the dominant renovation strategy,
accompanied by a magnitude of cost and disruption that may bring consideration to entire
building replacement.
3.5.7 Indoor Environmental Quality
The purpose of buildings is to create an interior environment that protects and shelters
occupants. Relative recent data has established strong links between aspects of the
interior environment and occupant health and productivity. People spend, on average, 90
percent of their time indoors (EPA 2017). The quality of this interior space in terms of
key measures of daylight, view, ventilation, thermal and acoustical comfort, is a
fundamental sustainability attribute.
Tall curtainwall buildings are increasingly used as human habitats in addition to work
spaces. Urban density, declining air quality, sound and light pollution are among the
factors that work to compromise indoor comfort. The toxic outgassing of indoor products
and materials is another factor that can compromise indoor air quality. There integral role
of the building façade in determining the quality of the interior environment is evident.
In mediating between the interior and natural environments, the building skin must
control moisture penetration, control air infiltration, heat transfer, solar radiation and
sound transmission. The façade also provides important connection to the exterior
environment through the provision of view to the outside, and natural ventilation through
operable vents. Design decisions must balance between these often-conflicting pursuits.
The use of vision glass in the building skin, for example, provides a desirable connection
to the natural environment, but is also a notoriously poor thermal and sound insulator,
and the use of too much glass can result in problematic solar heat gain and glare, in
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Natural ventilation is a practice that was largely abandoned with the advent of the tall
curtainwall building in the 1960s. Cheap fuel sources and powerful new air conditioning
technology combined to make this the dominant strategy of choice in providing the
interior thermal environment. The thermal impact of large glass areas in the building skin
was offset through the consumption of inexpensive fuels. This is not a strategy of energy
efficiency. New high-rise curtainwall buildings are exploring natural ventilation
strategies. The Tower at PNC Plaza (Pittsburgh, 2015, Gensler) is designed to be
naturally ventilated an estimated 42 percent of the year (PNC 2015), an accomplishment
for a building in this climate zone. The natural ventilation of this building type is not
easily accomplished. Strategies for natural ventilation must be fully integrated with other
elements of the building’s HVAC system and interior environmental control plan, another
example of the requirement for whole building design practices in sustainable building
development.
Holness (2009) claims that if the cost of occupants in commercial buildings is included in
lifecycle costing, that initial construction costs amount to only 2 percent, and operational
costs only 6 percent; the other 92% belongs goes to the workforce. Even minor
improvements in workforce efficiency could offset much of initial construction costs.
Indoor environmental quality is a dominant factor in providing for the health and welfare
of the building occupant. Studies have established the important link between comfort
and productivity (Wargocki et al. 1999; Roelofsen 2002; Jin et al. 2012; World GBC
2014;). Given the relevance of worker productivity (BLS 2016), the impact of health on
worker productivity (Burton et al. 1999), and the data links referenced above between
IEQ and health, the quality of the indoor environment is a vital sustainability attribute.
TCBs have long been used to provide office space, and their use as residential towers has
continued to escalate over past decades.
3.5.8 Integration
Integration is not a separate strand, but rather, the weave of the strand, the
interrelationship of the various attributes, which must all be considered if sustainability is
to be achieved (Figure 3.7). This is the challenge of the building skin, itself the nexus of
so many considerations—often competing considerations—effecting performance,
appearance and, ultimately, sustainability. The complexity of façade design comes in
balancing these various considerations in an integrated solution. Figure 3.3 reveals many
of the considerations converging at the building skin, providing a sense of this

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complexity, and also the important opportunities for integration with other building
systems, like mechanical and lighting systems.
Integration is used here as in the professional literature in the context of integrated
building design or integrated design process (WBDG 2016a; Augenbroe 1992; ASHRAE
n.d.), whole or holistic building design (Kim et al. 2011); Prowler and Vierra 2008), and
more particularly of building systems integration (NC State 2013; Rush 1986). Usage
tends toward generalization of involving more than one discipline or consideration in a
building design or process. Design-build, design-assist, and the AIA’s Integrated Project
Delivery, for example, are project deliver strategies aimed at involving diverse expertise
as early as possible in a building project, and managing that involvement throughout the
building process. While these delivery strategies have proven effective in managing the
escalating complexity of building construction, uptake has been tentative and slow (Kent
and Becerik-Gerber 2010, 815, 824). A similar pattern is apparent in other areas
attempting to embrace the concept of integration.
With respect to the building skin, integration refers both to the combined consideration of
the relevant issues diagramed in Figure 3.3, as well as the design and interaction of the
various technical systems intended to accommodate those issues. Progress is slow here,
as well. One of the best examples to date of façade system integration is the work done
by the Lawrence Berkley National Laboratory (LBNL) on the New York Times Building
(New York City, 2007, Renzo Piano Building Workshop and FXFOWLE). The project
involved an elaborate full-scale operational mockup to test the unprecedented integration
of lighting, sensors, controllers, roller-blinds and software to maximize daylight,
minimize electrical lighting, and prevent glare as a fully integrated automated system.
The test was conducted over the course of a year, with the participation of key industry
suppliers. A final system design was developed based on the test results, and installed
through an extended commissioning process (Lee and Selkowitz 2006).
Post-occupancy data was collected and reported (Lee et al. 2013) evidencing the
noteworthy success of the strategy. In spite of this, Selkowitz regards the effort as
unsuccessful because of its failure to scale up to broad marketplace adoption (Stephen
Selkowitz, email exchange with author, 10 August 2017), the explicit intent of the
Department of Energy and New York State Energy & Development, who provided
financial support to the development effort. In addition, to date there is no viable product

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integrating these functions available from a single-source provider in the marketplace,
despite the availability of all the necessary technology to do so. Selkowitz has been
heavily involved in soliciting involvement from industry to support this relatively simple
and straightforward development effort. Consequently, even this demonstrably effective
and much needed façade systems integration is only available on a costly customized
basis, and seldom employed. Figure 3.9 diagrams his vision of the opportunity in
automating this integrated functionality.
From a sustainability standpoint, the concept of integration necessitates attention and
response to all relevant considerations as a prerequisite to sustainable outcomes. An
effort that focuses only on operational energy performance, for example, may produce a
“green” or “high-performance” result, even one certified by one of the growing number
of green building rating systems, but it will not represent a truly sustainable outcome if
other measures of sustainability are ignored. The various green codes, standards and
rating systems are not particularly effective at this kind of integration, and under-
represent the central role of façade system performance.
Figure 3.9: Concept for automating façade system integration (courtesy of Selkowitz, LBNL).

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3.5.9 Resilience
The concept of resilience is the focus of Chapter 6.
The year 2011 did much to establish the reality of climate change even among skeptics
and deniers. It was a record year for weather disasters, with 14 separate events of at least
$1 billion each, together responsible nearly $60 billion in damages and 764 fatalities
(NOAA 2012). Fires, drought, floods, and severe storms are the order of the day, with
many leading experts predicting worsening conditions and warning that this is not a
temporary condition but a new era. NASA scientist James Hansen (2012) in an op-ed
piece in the Washington Post states:
This is the world we have changed, and now we have to live in it — the world that caused
the 2003 heat wave in Europe that killed more than 50,000 people and the 2011 drought
in Texas that caused more than $5 billion in damage. Such events, our data show, will
become even more frequent and more severe.
The current year of 2017 may well provide a new record. NOAA (2017) reported 9
weather and climate disaster events in the U.S. with losses of more than $1 billion each as
of July 7. Mark Zandi, chief economist at Moody’s Analytics, reports preliminary
damage estimates for recent hurricanes Harvey and Irma at up to $200 billion, potentially
equaling Hurricane Katrina losses (Zandi 2017).
Resilience is about learning to “live in it,” as Hansen puts it. The concept of resilience in
buildings is about life safety and economics rather than environmental protection, but
there is much commonality among these considerations and all fall within the
encompassing sphere of sustainability. Buildings and communities must be strategically
constructed in anticipation of prolonged adverse weather conditions to withstand severe
storm events, as well as other natural and man-made disasters. Considerations of resilient
design also include power disruptions, fuel shortages, and the potential for rapidly
escalating fuel and food costs that could make currently available products unaffordable
to many.
Tall buildings are alarmingly vulnerable to these unfolding conditions. Extended power
outages would render most of these structures uninhabitable. Tall buildings rely on
electrical power for lighting, vertical transport, water distribution, heating and air-
conditioning. Many do not have operable windows that could provide some level of

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natural ventilation in the case of failure of the building’s mechanical systems. Some
possess fuel-powered generators, but most are not designed to accommodate more than
short-term power disruptions.
The building enclosure is an obvious consideration in this context. A breach of the
building envelope exposes the entire building to extensive damage and its occupants to
the threat of injury and death. Here again tall buildings are uniquely exposed to the
adverse conditions presented by severe storm events. Wind speeds increase with
elevation. Glass is relatively fragile to the impact of windborne debris.
The landfall of Hurricane Andrew in 1992 and the catastrophic effects it had on life and
property in South Florida initiated a transformation in the approach to building in coastal
areas throughout the southeastern United States (Alvarez and Santora 2017). Increasing
population and urban density in these coastal communities, accompanied by urban
infrastructure including many high-rise office buildings and residential towers, is
threatened by an apparent strengthening of storm patterns in this area. Hurricanes Katrina
and Wilma have since provided additional evidence of the costly destruction that such
extreme weather events can bring. Local jurisdictions are responding to this threat in
various ways, but South Florida has taken the lead in developing and adopting code
requirements intended to mitigate loss of life, injury and property damage. Time will tell
if these code requirements accurately anticipated the magnitude and frequency of future
storms that may result from climate change. Façade damage and breach is only one
concern. Basic façade performance considerations of air and water infiltration under the
press of more frequent and stronger storm activity are among many unknowns that
accompany the uncertainty of future climate conditions.
Remarkably, a new crop of all-glass tall buildings has sprung up in recent years in
Miami. The glass facades on these buildings are claimed to be among the strongest
curtainwall systems ever constructed and have had to undergo rigorous performance
testing, including structural tests to loads in excess of 270 pounds per square foot in at
least one case (Glass Magazine 2011).
Resilience is strongly linked with durability in façade performance fundamentals, air
infiltration and water penetration primary among these. Façade design and construction
must be robust enough to maintain standards of performance through time in response to
the increased demands brought by climate change and other adverse conditions.

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Resilience is also linked with adaptability. The concept of resilience and these linkages
are discussed in Chapter 6.
3.5.10 Water
Humans can survive without oil, but not without water. Buildings are large consumers of
water. The U.S. Energy Information Administration (EIA 2012) reports that large the
46,000 large commercial buildings (greater that 200,000 square feet) used about 359
billion gallons of water in 2012, representing approximately 2.3 percent of the total U.S.
water supply. This translates to a bit over 50 gallons per worker per day. Water
consumption is a definite sustainability attribute in the building stock. Urbanization is
stressing water resources. Raskin et al. (1996 1-15) discuss growing pressure on limited
water resources in developing areas. Jackson et al. (2001) note that approximately 1-
billion people lack access to clean drinking water, with population growth fragmenting
water resources, and per capita fresh water availability declining.
Just as buildings will have to play a role in energy conservation and generation on the
road to zero-carbon, so will they necessarily play a role in water conservation, collection
and recycling. The façade system in TCBs will have to play a role in both respects. While
not a subject of this research, it is noted that there is potential in employing the façade
system in rainwater harvesting, and in some climate regions, potentially even the
collection of condensate.
3.6 Summary
There is little in the way of hard metrics to determine sustainability. The evaluation of
sustainability is largely contextual. A context must be created for the evaluation of TCB
façade practices. This chapter builds a set of relevant attributes of sustainability (Figure
3.7; Table 3.3) that can be utilized to evaluate a specific material, product, process, and
system. The attributes developed in this section are not intended as an exhaustive set; the
considerations of sustainability are abundant. Water, for example, a vital consideration,
has not been included in the evaluation criteria. The primary attributes to be applied here
include durability, energy (particularly embodied carbon), adaptability, heritage value,
and resilience.

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Chapter 4 — Skin deep durability: Extending service
life and quality of curtainwall systems to enhance
sustainability of buildings and urban habitat
4.1 Introduction
Metal-framed curtainwall systems are widely regarded in the building industry as high-
performance zero-maintenance systems (O’Mara 2014). Yet curtainwall systems are
routinely designed with no target service life and little consideration for durability
(Birschke 2005; Patterson 2014). The durability of metal-framed curtainwall, focusing on
embodied impacts, whether gaged as energy, carbon, global warming potential, or other
measures, is recognized as a significant component of a building’s environmental, social
and economic impact over its lifespan. Extending the service life of a building or building
system is a direct way to reduce associated embodied impacts, but must account for
recurring impacts over the lifecycle. Designing for durability, and the linked attribute of
adaptability, can also reduce energy and maintenance costs from building operations,
while improving service quality, over the service life of a building assembly.
The concept of differential durability (Kesik and Saleff 2005) recognizes that the
components that comprise a system each possess varied durability behavior and a unique
service life, and that the durability characteristics of the various components interact to
determine the ultimate service life of the assembly. Service life of an assembly may be
reduced to the least robust of its components, resulting in wasted durability and
amplifying embodied impacts. These criterion and others are used to evaluate
contemporary curtainwall technology. Building skin durability comprises many issues,

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requiring evaluation and strategies for integrating these considerations into the design and
delivery of new and retrofit façade programs. The primary components that comprise a
typical metal curtainwall assembly reveal service life characteristics requiring evaluation
of how these characteristics shape the service life of the assembly, and the implications
for embodied impacts. The causal forces of service life termination include degradation
and the complexities of obsolescence. Design practices can extend the durability of
curtainwall assemblies, and have implications for the design of new curtainwall systems.
Curtainwall assemblies are adding to the energy burden and environmental impacts of the
building sector by ignoring considerations of durability. Contemporary curtainwall design
and delivery processes are deficient in durability planning, and fail to provide service life
durations supportive of sustainable and resilient buildings and urban habitat. Alternate
ways of thinking about durability in façade systems should explored, in addition to the
potential of renewable systems that extend service life through planned maintenance
strategies.
Contemporary curtainwall practices are building future problems, even as the building
sector struggles with the legacy of the past, by failing to support service life duration and
quality consistent with sustainable building performance. Enhancing curtainwall system
durability can extend service life and quality, thereby amortizing embodied impacts over
a longer period and resulting in a significant reduction in environmental impacts, with
consequential contributions to the sustainability of the building sector.
The energy consumption and emissions profiles of buildings and the problem they
represent are now familiar: buildings consume three-quarters of all electricity and nearly
half of all energy in the U.S., while producing nearly half of all CO2 emissions
(Architecture 2030 2017). Much research and development has focused on improving the
operational energy performance of buildings; far less has focused on the considerations of
embodied energy and other embodied impacts (Cabeza et al. 2013). This is appropriate in
that energy consumed during the operational phase of a building dominates total energy
consumption. Yet energy consumed during the pre-construction, construction, and
deconstruction phases (embodied energy) is significant, and as efficiency gains are
realized in operational energy performance, embodied energy will come to represent an
increasing percentage of total building energy consumption. Cabeza et al. (2013)
performed a literature review on low carbon and low embodied energy materials in

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buildings and found variant definitions, but general agreement of their increased
importance in building lifecycle energy intensity, owing to the improving operational
efficiency of buildings. Also found was general agreement that quantification is currently
challenging, with no generally accepted measurement and quantification methodology.
Carbon emissions result primarily from the burning of fossil fuels. Reducing GHG
emissions from the building sector has largely focused on the burning of fossil fuels
during the operational cycle of a building; operational energy consumption produced
operational carbon emissions. Energy consumed during the construction and end-of-life
phases is called embodied energy consumption, and produces embodied carbon
emissions. The lifecycle environmental impact, or footprint, of a building, includes both
operational and embodied carbon emissions over the lifespan of the building, from
material extraction to reuse, recycling or disposal. The pursuit of carbon neutral design
and carbon neutrality in the built environment involves considerations of both operational
and embodied carbon, and the growing significance of the embodied component (La
Roche 2017; Sturgis 2017; Ibn-Mohammed et al. 2008). While technically different, the
terms embodied energy, embodied carbon, embodied GHG, and embodied global
warming potential (GWP) are commonly used interchangeably. The terms embodied
carbon, embodied GWP, and embodied impacts as a more generalized term, are used in
this chapter.
The relationship between durability, embodied carbon, and operational carbon in metal
curtainwall systems is a key sustainability consideration. The building skin impacts both
the appearance and performance of the urban environment. Yet curtainwall systems are
routinely designed with no target service life and little consideration for durability.
Contemporary curtainwall systems fail to support adaptability, durability, and service life
duration and quality consistent with sustainable building performance.
Sustainability goals in the built environment require that the durability of buildings be
reconsidered. Building construction is highly resource consumptive. Large commercial
and multi-unit residential structures in dense urban environments represent a particular
challenge. It is imperative that these buildings be adequately durable to support a service
life well beyond current expectations, and to provide a standard of service throughout that
lifespan consistent with sustainable performance. Durability is an often-overlooked
consideration of materials, components, assemblies, buildings, and cities, and yet is a

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fundamental attribute of sustainability, and an increasing focus of the green building
movement (Brock 2005, 9).
Extending the service life of a building or building system is a direct way to reduce
associated lifecycle embodied impacts. Designing for durability can also reduce energy
and maintenance costs from building operations during the service life of a building
assembly. Issues of differential durability may reduce the service life of an assembly the
least robust of its components, resulting in wasted durability. These criterion and others
are used to evaluate contemporary curtainwall technology. High-performance facade
assemblies are adding to the energy burden and environmental impacts of the building
sector by ignoring considerations of durability. Strategies to extend the service life of
these assemblies are needed.
The primary components that comprise a typical metal curtainwall assembly reveal
service life characteristics, how these characteristics shape the service life of the
assembly, and the implications for embodied energy impacts. Façade system maintenance
requirements and renovation cycles are a strategy to extend service life. Design concepts
for extending the durability of curtainwall assemblies are explored, along with the
implications for the design of new curtainwall systems. Architectural glass is an example
to explore strategies for significantly extending the service life of key façade assemblies,
and ultimately the façade system.
The various green building rating systems largely ignore durability (Brock 2009, 9).
Strategies for extending service life include improved system design, the use of more
durable materials, and a renewal process incorporating cycles of maintenance and partial
renovation. However, each of these strategies presents potential offsets in the form of
recurring cost and embodied energy inputs for repair, maintenance and renovation, which
must be considered in any comparative assessment. With respect to metal-framed
curtainwall systems, a core question is: Does a renewal strategy incorporating
maintenance and partial renovation cycles to extend service life provide advantages over
a reclad renovation strategy where the entire façade system is removed and replaced at
the end of its service life over the building lifespan? This, then, becomes central to
whether or not:
The service life of metal curtainwall systems can be extended through a renewal strategy
incorporating planned maintenance and partial renovation cycles, thereby providing

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advantages that improve building sustainability as compared with a replacement
renovation strategy.
Curtainwall design, delivery and renovation practices are accepted largely without
question or discussion but must be challenged as civilization steps toward a sustainable
built environment. Enhanced durability can extend the service life and quality of facade
systems producing health, comfort, and sustainability benefits (chapter 4). The
Millennium IGU is a concept for an insulating glass assembly that poses no compromise
to the recyclability or durability of float glass and optimizes the lifespan of the IGU. The
concept illustrates an alternative way of thinking about the challenges presented by the
pursuit of green building practices.
Durability is explored in the context of the building skin, including an examination of the
dominant issues, their significance, and strategies for integrating these considerations into
the design and delivery of new and retrofit façade programs. Section 4.2 following
develops the context for the research described in this chapter. Section 4.3 establishes
relevant definitions and concepts to frame the discussion, and documents an extensive
literature review. Following sections present and discuss the research findings. Section
4.4 analyzes the durability and embodied carbon characteristics of the primary materials
and components that comprise a curtainwall system. Guidelines to enhance façade system
durability and embodied carbon behavior are developed, and Section 4.6 provides a
summary, conclusion and discussion of the findings. Contemporary curtainwall design
and delivery processes are found to be deficient in durability planning. Curtainwall
systems fail to provide service life durations supportive of sustainable and resilient
buildings and urban habitat. Sections 4.4.8 – 4.4.12 explore different ways of thinking
about durability in façade systems, and consider the potential of renewable systems that
extend service life through planned maintenance strategies.
4.2 Context
Durability is a primary attribute of sustainability. Danish architect Bjarke Ingalls (2011)
claims that sustainability is a design problem. There is some urgency to solving this
problem, as Meadows (2004, loc. 341) expresses in Limits to Growth: The 30-year
Update:

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Levels of affluence we might have provided sustainably to all the globe's
people are no longer attainable; ecosystems we might have preserved have
been extinguished; resources that might have given wealth to future
generations have been consumed.
The term sustainable suggests the idea of permanence, continuous, on-going, and can be
translated in several languages (French, Dutch, Finnish) as durable (Bourdeau 1999,
358). Durability is a key component of sustainability, and one too often neglected in the
building industry, where current standards for durability fail to support sustainability
parameters (Kesek 2002, 314; Haagenrud 2004,1). Amidst continued concerns with fossil
fuel consumption, material scarcity, environmental impacts, progressive degradation of
built environment, and the high cost of building construction, renovation, maintenance,
repair, the issue of durability is emerging as a predominant concern (Beer et al. 2011).
Contemporary buildings and their major components are products of industrialized
society. The value of these products is linked with longevity—service life—and in many
cases, does not support sustainability (Kostecki 2008).
Nireki (1996, 403) states that “Durability is an important factor that cannot be ignored
when considering the performance of buildings,” and references related sustainability
attributes. Yet durability considerations of buildings and their major systems are poorly
understood, and rarely included in building programs both large and small. Service life
duration, as an expression of durability, is rarely specified, even for large building
programs certified under one of the green building rating systems. A material supplier
asked about the service life of their material or product will often respond with warranty
information, not understanding the question.
Kesik (2002, 313) comments that the consideration of durability as a sustainability metric
is unavoidable given the temporal measure of other metrics quantifying impacts over the
service life of a building or building system. These impacts include economic,
environmental degradation, resource depletion, global warming potential, and bio-
diversity reduction. The combination of these metrics in the pursuit of holistic building
solutions can yield surprising and even counterintuitive results. Much depends upon
durability and the duration of a building’s lifespan.
Silva (et al. 2016) identify drivers of an emerging market consideration of durability:

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§ growing owners interest in establishing design service life requirements
§ growing stakeholder awareness of lifecycle costs as they include maintenance and
repair in addition to construction
§ knowledge that durability is key to quality and performance
§ understanding that aging and visual appearance are a performance consideration
§ heightened awareness among owners and insurers of risk and liability of failure of
construction elements (including premature end of service life)
Reducing embodied impacts is not simply a matter of material selection (Cole and
Kernan 1996, 317). The maintenance, repair and replacement of materials produces
significant recurring embodied impacts bringing importance to issues of
§ material/system longevity
§ reparability
§ maintainability
§ replaceability
§ adaptability
The need is to transition from a period where first cost considerations have predominated;
reliable predictive methodologies for service life and maintenance requirements have
been inadequate; and where lifecycle thinking and practices in the building industry have
been largely absent (Lounis et al. 1998). Meadows (2014, ix) emphasizes the relevance of
sustainable service life planning as “applied lifecycle thinking,” and a process where
economic issues are important but not central.
In the context of the foregoing, and the growing appreciation for the façade system as the
outermost building layer protecting structure and interior finishes and furnishings, the
building skin becomes a primary focus. The façade system is prone to defects because of
environmental exposure, the results of which can directly impact the quality of urban
habitat as well as interior environment, with significant associated repair and renovation
costs to society (Kirkham and Boussabaine 2005). All of this has led to far greater
awareness of the façade system as an integral, even pivotal aspect of building design
(Schittich 2002).
In fact, building facades have a service life distinct from building service life, and one
that can, and often does, ultimately become the determinate for building service life,

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triggering major renovation and even building demolition. Despite the increasing
awareness of durability referenced above, it remains uncommon for service life
expectations to be defined for new building projects (Birschke 2005; Patterson 2014).
Moreover, there is also no consensus on how long a building should last, even as the
many variables that represent variations of the building stock are constrained to narrow
typologies. The forces that impact service life are poorly understood in practice.
For example, the Woolworth Building in New York City turned 100 years old in 2013
amidst a large-scale office renovation and luxury condominium conversion of the upper
floors. The structural systems of such buildings are generally regarded as having a life
span of several hundred years, if not longer. Large-scale building projects should include
durability planning that supports a building service life measured in hundreds of years,
and, at least in the case of monumental buildings, a 1000-year service life may be both
appropriate and achievable. Furthermore, the other major buildings systems must be
designed in harmony with the intended building service life; perhaps most importantly
the façade system, which both protects and integrates with the structural system to form
the building shell.
A new building form emerged in the early twentieth century and proliferated in the 1960s
and beyond—the tall curtainwall building (TCB)—is now recognized as a hallmark of
Modernism (Jerome 2011). Early icons of this building type include the U.N. Secretariat
Building, Seagram Building, and Lever House. These were followed by a plethora of
lesser quality buildings in major urban centers in North America and Europe; the
emergence of a building type that Wigginton (1996, 96) characterizes as “a sort of
‘International Style’ without the style,” and as having “intrinsic weaknesses in
technology and performance.” The biggest problem with these early TCBs, however, is
that they were essentially designed as throwaway buildings, with no consideration of
durability, and the adaptability necessary to resist the forces of acquiescence (Browning
et al. 2013, 9-11). Low ceiling heights, deep floor plans, and short bay widths may make
them unsuitable as renovation candidates, subjecting many of them to demolition and
replacement at a significant cost in both money and energy at a time when reducing
carbon emission is imperative.
Contemporary Western culture has long assumed an unfolding future of continual
renewal drawn from limitless resources, a worldview in which the concept of durability

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finds little purchase (Cooper 2010). Appreciation for durability and longevity fell victim
to a throwaway mentality that emerged as a byproduct of the industrial revolution
(Cooper 2005) and grew to strength in the mid twentieth century, at the same time as the
wholesale adoption of the new lightweight curtainwall technology in place of the long
prevailing masonry practices. This throwaway mentality persists—a mentality that
extends to buildings themselves—and has propagated overflowing landfills across the
landscape. A report on tall buildings in New York City stands as an indictment of past
architectural practice (Browning et. al. 2013). These first-generation glass buildings
constructed 1958 – 1973 were often poorly designed for conditions of changing use, and
fundamentally under-designed with respect to evolving code requirements and changing
climate conditions. They were typically single-glazed, some with structural systems so
deficient by current minimum code standards as to be unable to accommodate the
additional weight produced by a retrofit from single to double-glazing. Many of these
buildings are badly in need of renovation, but low floor-to-floor heights, tight column
spacing, and the difficulty of achieving compliance with basic code requirements,
represent substantial challenges to building upgrades to current Class-A standards
(BOMA 2017). The BOMA report identified a large body of buildings that are reaching
or have passed the limit of their serviceability at 50-60 years of age. Unlike the 100-year-
old Woolworth Building, many of them may prove unsuitable for renovation. The
report’s authors interviewed some of the architects that had produced buildings included
in the study’s survey, and they expressed a widespread implicit assumption as common at
the time, that the buildings they were designing would see a service life of only about
twenty years. The study suggests that many of these buildings are not viable candidates
for deep energy retrofit in today’s regulatory and economic environment, and that
demolition and rebuilding may be the only solution.
While attitudes about reuse and recycling have changed in the growing green
consciousness of the new millennium, demolition and construction waste currently
represents a significant percentage of the solid waste stream. New construction projects
generate 3-5 pounds of waste per square foot, while renovation projects cam be 20-30
times more (Strain 2017, 6). Responsible waste management is an obligation of advanced
civilization, and another primary attribute of sustainability. Zero-waste scenarios as
embodied in the circular economy are the solution (Ellen MacArthur Foundation 2017),
and are fully embraced in this research inquiry. These include concepts of biomimicry
with nature as the model for sustainability and closed-loop systems theory that integrate

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no end of life, but an ongoing process of renewal where all things are repurposed and
reused as a priority, and fully recycled where reuse is impractical or impossible (Lieder
and Rashid 2016; Meadows 2012; Kesik and Saleff 2009, iv).
New thin and lightweight curtainwall cladding technology owes its early success to
largely economic drivers. In contrast with the masonry wall infill practices of the time,
these new systems were lighter, quicker to install, maximized leasable space, and
presented a modern aesthetic (Wigginton 1996, 96). Utilizing new materials and new
manufacturing and installation processes, this emergent cladding technology was
essentially experimental in nature (Ayón and Rappaport 2014, 18; Jerome 2011, 152;
Prudon 2008, 30). Given the experimentation and widespread disregard for issues of
longevity, it is not surprising that sixty years later many of these façade systems have
fallen below the level of minimum acceptable quality (Ayón and Rappaport 2014). They
persist because of the magnitude of cost in dollars and disruption required to remedy the
problem.
Research to date suggests that replacement is the most common curtainwall retrofit
practice (chapter 7). This is an inadvertent consequence of design intent: curtainwalls are
designed as zero maintenance systems and not intended to accommodate maintenance or
partial renovation. Thus, some 40 years later when façade renovation is considered, the
replacement scenario is typically the most cost effective simply because other strategies
(such as glass replacement) are impractical or impossible. This practice effectively limits
the service life of the curtainwall system to a range of 35 to 60 years depending upon the
system design, conditions of use, and service environment.
The most dominant materials employed in curtainwall systems are glass and aluminum,
both with high embodied energy content. Strain (2017, 6) calls for minimizing the use of
“emission intensive materials,” specifically citing aluminum and glass. Both are highly
durable materials, however, and extending service life can significantly dilute the
embodied energy impact. Brock (2009, 9) notes that the longer a system or component
functions, the lower the embodied energy per year of use. Annealed float glass, the raw
product of the float glass process, has an indefinite lifespan in the building skin: good
until broken. In a curtainwall system, however, float glass is reduced to the 35 to 60-year
service life of that system, or when used as an insulated glass unit (IGU), may reduce the
service life of the façade system itself to the service life of the IGU: approximately 20 to

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25 years. Aluminum and the aluminum finishes exhibit a similar pattern. The result is
significant wasted durability in both materials.
This problem is exacerbated with glass because the material is not recycled and enters the
solid waste stream ending up down-cycled or as landfill. Aluminum can at least be
recycled, thereby reducing embodied impacts, although not as favorably as reuse.
According to the Aluminum Association (2017):
§ aluminum is infinitely recyclable,
§ recycled aluminum products require less than 10% of the energy consumed in the
production of new aluminum, and
§ 95% of aluminum in buildings is recycled.
Another impact resulting from the replacement strategy is the problematic disruption to
ongoing building operations. Mitigating the potential economic losses associated with the
loss of use of the space often requires that buildings remain occupied and as functional as
possible throughout the renovation process. Regardless, managing disruption thus
becomes the driver in most façade renovation projects, even exceeding cost as the
predominant consideration.
The problematic legacy following from the circumstance of replacement as the only
viable façade renovation option:
1. Even in the current time of economic prosperity and a booming construction
market, renovation decisions are being delayed, compromising energy efficiency
and subjecting users to substandard interior conditions with potential implications
to comfort, health and productivity.
2. Owners are pressed to consider demolition and replacement of the entire building
as a more financially attractive alternative. Beyond the embodied impacts and
load to the solid waste stream represented by demolition, the financial metrics
favor the replacement of the older building with a larger one as proposed in the
Midcentury (un) Modern report, likely a step in the wrong direction (Addington
2008, 158).
Thus, the façade system threatens to be the weak link in determining the building service
life. As a body then, these tall curtainwall buildings pose a significant challenge for the
transformation to sustainable urban environments.

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Glass and metal-framed curtainwall systems emerged from this experimental period to
become the dominant façade technology for large commercial buildings, including high-
rise residential structures. It is important to reconsider this technology, in its current as
well as its initial form, particularly with respect to issues of durability. Curtainwall
practices are no longer emergent and experimental as they were in the mid-twentieth
century, yet fundamental problems that compromised the durability of these systems
remain today. The general failure to consider durability and service life in current
construction practice is cause to speculate as to the magnitude of future problems under
construction today, even as the building sector struggles with the legacy of the past.
4.2.1 The time value of carbon
A high-performance façade system with a high embodied-GWP profile coupled with a
long service life, may prove more sustainable than a lower embodied-GWP alternative
coupled with a shorter service life, owing to the reduction in operating cycle impacts and
the amortizing of the embodied impacts over a longer time period. But this ignores the
consideration of the time value of carbon.
The time value of carbon amplifies the importance of embodied energy as a consideration
in building design (Karimpour et al. 2014, 109; Marshall and Kelly 2010). Strain (2017)
emphasizes the urgency of short term reductions in carbon emissions. Building
construction and operation is responsible for nearly half of U.S. GWP. New building
projects often incur a large upfront energy expenditure representing embodied impacts
that may take decades to repay in the form of energy savings from operating efficiencies.
Materials represent 60-80% of embedded carbon for a typical office building in North
America (Simonen et al. 2017). This emphasizes the importance of 1. minimizing
material usage, 2. material selection in new construction and renovations, and 3. building
reuse as a priority over new building construction. In addition, larger and heavier
buildings embody higher emissions on an area unit basis (Strain 2017, 5).
The replacement of old buildings as suggested in the Mid-century (un) Modern report,
even if the replacements are far more energy efficient, represents a near term increase in
the embodied carbon debt. Yet improving the energy efficiency of existing buildings is
critical. This will be challenging to accomplish with older tall curtainwall buildings
without façade interventions. The dominant practice of façade replacement, however,
presents a challenge in the form of high embodied impact, significantly offsetting the

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energy efficiency benefit provided by the new façade. The dilemma presented by the old
curtainwall systems is itself embodied in the assessment of Strain (2017, 8), where on one
hand he suggests that replacing an aluminum and glass curtainwall may not be a good
carbon investment, while on the other hand pointing to the opportunity in energy savings
represented by underperforming facades with “little or no insulation, single glazed
windows, unshaded windows, leaky, drafty building.”
4.3 Dimensions of durability
Durability is a complex issue with many and diverse considerations that ultimately
combine with a significant impact on performance of the building sector. Nonetheless,
durability and its many aspects are poorly understood and integrated into building design
and construction practices. The consideration of durability is especially relevant to the
building skin.
4.3.1 Why durability is important
The concept of durability involves the degradation behavior of a material, system or
building over time in a specific environmental context. It is sometimes referred to as
weathering, especially in the context of exposure to the outdoor elements. Durability
determines the service quality of a building over its lifespan, as well as the duration of
that lifespan. The implications of premature durability failure are costly to building
owners, users, and ultimately to society. These costs are not limited to repair,
maintenance, renovation and replacement of a building or its components, but include
lost productivity, compromised occupant health leading to absenteeism and health care
costs, and increased operating costs (Iselen and Lemer 1993, 1). Considerations of
comfort, health and productivity add a social dimension, in addition to the environmental
and economic dimensions, to the potential impacts of durability. These problems are
apparent in the stock of tall curtainwall buildings constructed in the early second half of
the last century, and result from curtainwall system designs that fail to anticipate and
accommodate the need for maintenance, future retrofit and renovation (Patterson et al.
2012). These design deficiencies remain in practice today, with each new large
commercial curtainwall building under construction representing the potential for future
compromised building performance and unanticipated repair, retrofit and replacement
costs. Understanding the causal forces at work and acting to mitigate them involves

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planning and programming through the entire building lifecycle from design through
disposal.
A major building project requires significant material resources. At the moment of
construction completion, these materials embody a measure of environmental impacts
resulting from their cumulative extraction, processing, transport, handling, and
installation. The sum of these impacts comprises the footprint of embodied environmental
impacts for the building, whether measured in terms of energy, carbon or carbon
equivalents. Thus, buildings incur a considerable debt of embodied environmental
impacts even before the doors open. As buildings commence their operational cycle they
begin a new accumulation of impacts, long thought to far exceed the embodied impacts.
Evidence suggests, however, that embodied impacts may represent as much as 30-40% of
the combined lifecycle impacts over a 40-year service life (Crowther 1999, 2). As
buildings become increasingly efficient in energy consumption over their operational
cycle, this percentage will increase. Once constructed, the only factor that can mitigate
the initial embedded impacts is time; the distribution of impacts over a longer timeframe.
Given the magnitude of impacts and the influence of service life, the general failure to
appropriately address durability in building design represents a gap in best practices.
4.3.2 The expression of lifespan
How much does your building weigh? – A question asked of architect Norman
Foster by R. Buckminster Fuller in 1978, as they viewed Foster’s recently
completed Sainsbury Centre for Visual Arts (Foster 2002, 4). The unasked
corollary: How long will it last?
Durability terminology discussed herein is largely derived from the Canadian Standard
Association’s CSA 478-95 Guideline on Durability in Buildings (CSA S478-95. 2007),
as discussed in Service Life Considerations in Relation to Green Building Rating Systems
(Athena Institute 2006, 4-8).
Durability
The ability of a building or any of its components to perform its required
functions in its service environment over a period of time without unforeseen
cost for maintenance or repair.

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The various definitions as discussed by the Athena Institute (2006, 4) are relevant, as they
consider façade systems directly, but it is often useful to consider neighboring industries
and technologies, not simply to test the conditions in the native silo, but also as a
potential source of insight and even the transfer of relevant ideas and principles. Cooper
(1994, 5), with a focus on consumer products, posits a nearly identical `definition of
durability:
…the ability of a product to perform its required function over a lengthy period
under normal conditions of use without excessive expenditure on maintenance
or repair…
suggesting a link between buildings and products. This is not a new idea. Architects and
designers like Norman Foster, Richard Horden, Charles Eames and others have long
pursued this concept in their work and research. The relevance of the relationship is
nuanced; buildings are considerably different from complex consumer products
(Khasreen et al. 2009, 677), and attempts at transferring principles from one to the other
must account for these differences. Factors that contribute to these differences include
lifespan; buildings generally have a longer lifespan than most products, with product
lifespans ranging considerably from under a year for many disposables such as plastic
shavers and single-use cameras, to automobiles, with an average lifespan of 11.5 years
(IHS n.d.). In contrast, commercial buildings in the U.S. have a median lifespan of 70-75
years (PNNL n.d.). In this context, it is surprising that Cooper’s definition employs the
temporal qualification of “lengthy” while the Athena definition imposes no such
qualifier.
Amplifying the impact of building’s lengthy lifespans is the likelihood of changes to
form and function over that lifespan, changes that can significantly alter a building’s
lifetime energy profile. In addition, buildings are site-built: essentially complex, one-off
constructs, each to a greater or lesser extent customized to conditions of site, climate, use,
owner preferences, and other factors (Meadows 2012). Products are typically mass-
produced in great numbers of identical units. There is little in the way of standardization
in large commercial buildings and their façade systems, where aesthetic differentiation is
an implicit goal. These and other factors combine to render the building industry unique
and markedly different from most other complex products.

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Yet the body of work regarding product durability and service life: factors that impact
service life; the concept of obsolescence; tools and methodologies for predicting service
life; is more diverse and robust than for buildings, and provides useful insights into
buildings and construction processes. Thinking in terms of product lifecycle for example,
is more pervasive and with a longer history than with the building industry (Khasreen et
al. 2009, 677). Important product concepts, such as obsolescence, can be usefully
translated and tested for relevance to buildings and the building industry. Davies and
Szigeti (1999, 1856-7), for example, discuss tools and processes measuring building
functionality and serviceability as a means to improve service quality and avoid
functional obsolescence.
Service Life
The CSA (S478-95. 2007) defines service life as,
The actual period of time during which the building or any of its components
performs without unforeseen costs or disruption for maintenance and repair.
Service life for a building, then, is the period of use from initial occupancy to final
disposal; for the façade system, from initial installation to final removal and disposal.
Cooper (1994, 8) concurs with service life definition, but differentiates the terms Service
Life and Technical Life, with the latter as the “maximum period during which [a product]
has the physical capacity to function,” noting that this potential is rarely achieved for
various reasons discussed later. This definition of technical life is related to the CSA
definition for:
Predicted Service Life
The service life forecast from recorded performance, previous experience, tests
or modeling. CSA (S478-95. 2007)
Another durability metric most useful to the design team, design service life is that
designated by the architect or owner in the context of anticipated service conditions and a
prescribed maintenance plan (Nireki 1996, 403). Design service life is the target lifespan
of a building to be established at the outset of a building project as an aspirational goal,
with a characteristic behavior pattern as indicated in Figure 4.1. Design detailing,
material selection, and the design of major systems and components can then be guided
by this target.

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Design Service Life
The service life specified by the designer in accordance with the expectations
(or requirements) of the owners of the building. CSA (S478-95. 2007)
Figure 4.1 provides a graphic representation of service life.
Lifecycle is an equivalent term to lifespan or lifetime, but brings focus to the cyclical
nature of the system to which it is applied. In buildings, that would include cycles
spanning the full building process from materials extraction to disposal, including
preconstruction, construction, operation, disassembly and disposal; a cradle-to-grave
context. The term has been integrated in the discipline of lifecycle assessment (LCA).
Basbagill (2013) emphasizes the importance of LCA as an early stage design tool, but
Heiskanen (2002, 427-8) suggests that the greater value of LCA lies beyond formal use
of LCA tools and methodology, in the way it is stimulating a pervasive awareness of
product lifecycle that is migrating through adjacent disciplines and practices, such as
environmental design, supply chain management, product labelling and policy, what
might be called lifecycle thinking: “…a life-cycle world view is becoming part of current,
late-industrial culture in the Western world.” Thinking in terms of the full lifecycle when
designing a building seems self-evident. Lifecycle thinking is not new to construction
(Schlaich and Potzl 1992, 55), but the building industry has been slow to adopt this

Figure 4.1: Conceptual diagram of service life (adapted from Iselin and Lemer 1993, 16;
Kesik 2002).

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practice, as evidenced by the fact that a design service life is only rarely specified for
buildings (Rauf and Crawford 2015, 141; Meadows 2012; Stevens 1992, 25). Even
LEED Platinum tall building projects are typically designed with no requirement for a
minimum building service life. LEED version 4 launched in 2013 is the first version to
require a minimum specified service life, and then only as prerequisite for the single
durability point possible under the point scheme. Sixty years is itself undershooting,
particularly with respect to TCBs. The conclusion here is that a lifecycle perspective is
critical to evaluating considerations of sustainability.
Differential Durability
Another important concept in the evaluation of buildings and building systems for
durability is that of differential service life, or differential durability, defined by Kesik
(2002, 2-4) as: “The service life difference between the components of a material or
system of a building.” Buildings and their facade systems are multi-layered constructs,
with varying magnitudes of sheer forces between the layers and with the potential to
literally tear themselves apart over time (Brand 1994, 12-13). Imagine an automobile not
designed to accommodate the periodic replacement of tires, necessitating disposal when
the tires became unserviceable, and the resulting wasted durability of the remaining
assembly. The remedy is to identify, design and plan in response to the relative durability
and service life characteristics of these layers to harmonize their behavior over the
building lifespan.
Service Quality
Kesik (2002, 2-3) also discusses service quality as the functional and aesthetic
performance of buildings or their façade systems in relation to 1, specified requirements
and 2, the perceptions and expectations of stakeholders, as diagrammed in Figure 4.2.
This dual standard presents something of a dilemma: specifications are generally
quantitative, measurable and verifiable, while perceptions are qualitative and prone to
change over time, having important relevance to considerations of obsolescence, (Section
4.3.6). For now, note that these qualitative measures are most often the deciding factors
in service life determination.
Service quality sets the bar for
§ new service condition
§ target quality (for planned maintenance and renovations)

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§ minimum quality (below which maintenance or renovation is required)
These set points are guidelines; the unfortunate reality is that the performance criteria
defined in project specifications for new service or post-renovation target service quality
often goes unverified and unrealized (Cooper 2001). In addition, service quality may drop
below minimum standards with no corrective intervention forthcoming, often due to
economic considerations (Ma et al. 2012, 889-90), with deleterious consequences to
building occupant comfort, health and productivity (Jin et al. 2012).

Figure 4.2: Area under curve equals durability, making component #2 the more durable. (Kesik 2002,
3)
4.3.3 Beyond operational energy: Embodied carbon
The high-performance and green building dialogue is too often constrained to the energy
consumed during building operations. It is increasingly recognized that embodied
carbon—the emissions resulting from primary energy consumed during the material cycle
from extraction through end-of-life and disposal—becomes an integral building
performance consideration. Embodied carbon was long regarded as less than 10-20% of
lifecycle building energy consumption (Ramesh et al. 2010, 1592-600), and relatively
unimportant, but this is changing. As improvements are made in operational carbon
efficiency, embodied carbon assumes an increasing percentage of building lifecycle
emissions. Evidence suggests that low energy buildings have a higher embodied carbon

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profile than conventional buildings, even as their lifecycle energy consumption is
significantly lower (Sartori and Hestnes 2006, 256-7). Karimpour et al. (2014)
demonstrate climate as a relevant factor in lifecycle energy analysis; the embodied energy
profile of buildings in a mild climate can be 35% of future emissions. Cole and Kernan
(1996, 315) project that embodied impacts could represent as much as 65% of lifecycle
energy costs for a typical office building. Rauf and Crawford (2015, 147) found 50-60%
of lifecycle energy as embodied energy in a residential study.
Even the benefits of building energy retrofits can be reduced or negated by embodied
impacts. Frey et al. (2011, 84) found that reduction in energy consumption by 30% could
take 10 to as much as 80 years for the accumulated energy savings to offset the embodied
energy debt resulting from the retrofit. If the remaining building lifespan proves to be less
than the payback period, the result is a net energy loss. This highlights the potential
impact materials have in construction and renovation projects, and the critical role of
material selection.
This is particularly relevant to curtainwall technology, as the curtainwall system
represents a significant percentage of a building’s embodied carbon because of the high
energy intensity of the primary materials. Aluminum and glass are both high embodied
energy materials, largely because of the energy used in their manufacture and transport.
Richards (2015) claims unitized curtainwall systems could be as much as 30 percent of a
building’s embodied carbon footprint, and in a refurbished building where the structural
system is retained, as much as 50 percent. Their relatively short lifespan further amplifies
their lifecycle embodied carbon footprint.
The embodied impacts of a building are the aggregate of the embodied impacts of the
constituent systems and subsystems, down to the individual material and product
components that make up the building. Embodied impacts are assessed over a defined
time period, bringing the related concepts of service life and durability to the forefront.
Durability is not an inherent property of a material or system. It is a measure of
performance, in this case resistance to degradation, in a specific service environment over
time, e.g., low-carbon stainless steels exhibit higher corrosion resistance than mild steel
in coastal environments. One material may be more durable than another in one service
environment, but not in another. A material may be more durable than another over a

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broader range of service environments. Characteristics of durability are important in
durability planning.
Service life defines the temporal context for durability. Service life is the time that a
material or system will meet a defined level of performance in a specific service
environment. Durability planning involves matching design service life—as specified by
the building designer or owner—with predicted service life, as “forecast from recorded
performance, previous experience, tests, or modeling” (CSA S478-95. 2007). Building
materials and systems are assessed for durability during design development, with the
goal of a building that will ultimately provide the desired service life, while minimizing
maintenance requirements. Durable materials generally, but not necessarily, require less
maintenance over their lifespan (Wilson 2005, 1).
The linkage between service life and lifecycle embodied impacts (Grant 2010, 175-6;
Grant et al. 2014, 197). Durability relates directly to lifespan—a more durable building
lasts longer. The economic costs are spread over a longer time, during which the building
can be in continuous use. Similarly, the environmental costs produced by the combined
sum of materials and energy consumed in its construction, and their associated impacts,
are effectively amortized over this extended time. Peter Yost (n.d.) with BuildingGreen
states that doubling the lifespan of a building halves the environmental impacts resulting
from its construction. This is a simplistic generalization neglecting the issue of
maintenance. If maintenance is required to achieve the increase in service life, the energy
and related impacts resulting from the maintenance add to the lifecycle embodied
impacts. Maintenance requirements tend to escalate as materials and systems age.
Maintenance, repair and renovation activities over a building’s lifespan are referred to as
recurring or recurrent embodied energy, a component of a building’s lifecycle embodied
energy. As Kesik (2002, 315) notes, evidence suggests that most buildings are in service
beyond 50 years, with growing recurring embodied energy expenditures as the building
ages beyond this half century mark and retrofits begin to address the combined effects of
deterioration and obsolescence. This is especially true of tall and large commercial
buildings.
Nonetheless, researchers have linked extended service life with reduction in lifecycle
embodied energy while including recurrent embodied energy considerations. Cole and
Kernan (1996, 307-17) show that lifecycle embodied impacts are reduced with increasing

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lifespan. Fay et al. (2000, 31-41), in a residential study, found a 15%reduction in
embodied energy in extending service life from 50 to75 years. Rauf and Crawford 2015,
reduced lifecycle embodied energy by 29% when increasing service life from 50 to 150
years in another residential study.
Utilization of materials, products, and system designs with enhanced durability can
potentially extend the service life of buildings and their major systems, thereby reducing
embodied GWP. Extending service life as a strategy to minimize embodied GWP
requires accounting for the energy and environmental impacts of all materials that
comprise the system, along with their repair and maintenance requirements, over the
extended lifespan. Durability generally comes at a cost, both economically and
environmentally; more durable materials are often more expensive and themselves
embody higher environmental impacts. Analysis is required to assure that the extension
of service life, including maintenance requirements, provided by more durable materials
or systems, is adequate to justify these higher costs by producing a net reduction in
embodied GWP over the building lifecycle.
Designs developed to reduce operational energy consumption often ignore the embodied
GWP debt resulting from the materials employed in the energy-saving solution. Building
elevations are sheathed in elaborate screens and shading devices to prevent solar heat
gain. Double-skin facades add an additional layer of building skin to improve system u-
factor and solar performance. The substantial increase in material resulting from design
strategies adds to the embodied GWP debt of the double-skin system, and offsets the
operational energy savings achieved by the high-performance design. It can take many
years of operational energy savings to offset the added embodied GWP debt. Another
example is the trending use of triple-glazing as an energy saving strategy over double-
glazing. Circular Ecology (Jones 2014) published a report examining the payback period
of energy savings of a triple-glazed unit to offset the additional embodied energy debt of
the triple-glazed as compared to the double-glazed unit. The analysis revealed that it took
about twenty years before the operational energy savings offset the additional embodied
GWP of the triple-glazed unit. As twenty years is the approximate service life of an IGU,
this calls into question the real value added using triple-glazed products. A double-glazed
product would provide a net GWP benefit over a triple-glazed product in any application
where the actual service life was less than 20 years.

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4.3.4 Supply chain considerations
Unfortunately, the cost of materials and products does not generally reflect their
embodied impacts. Cheap labor, for example, in some remote part of the world, can make
it cheaper to ship product around the world to the jobsite than to buy an equivalent item
close by, even though the difference in transport costs and associated embodied impacts
are far larger.
Embodied carbon impacts start with material extraction and track those materials through
fabrication cycles and transport, ultimately to the job site for installation in new
construction of as repair or renovation to an existing building. These activities all require
energy, water and other resources, with related emissions and environmental impacts.
Manufacturers refer to the various materials and components required for in support of
production processes as the supply chain, and supply chain management is a major focus
for enterprises such as automotive manufacturers. In comparison, supply chain
management in the building industry tends to be fragmented and far less sophisticated.
In recognition of the embodied impacts represented by supply chain activities, some
green standards and rating systems have attempted to address this consideration. LEED,
for example, has long rewarded “regional” materials sourced within a specified radius
from the job site. This is intended to incentivize the procurement of more local materials
and products, as opposed, for example, to buying from a cheaper offshore source. LCA
for a material, product or building, typically involves a detailed examination of the
supply chain. There is some surprising supply chain behavior with embodied GWP
implications in the supply of curtainwall systems, discussed in section 4.4.9.
4.3.5 Differential durability: The compounded complexity of
building assemblies
Today, buildings and their primary systems are typically complex, layered, highly
engineered assemblies (Kesek 2002, 2; Bell 2009, 10-15). Raw float glass, for example,
is rarely used in new building construction. It is commonly found in the single glazed
windows and façade systems prior to the mid-1970s, when the energy crisis of 1973
accelerated the adoption of insulated glazing products in the form of the double-glazed
IGUs of the time (Arasteh 1994, 339-340), what Wigginton (1996, 265) refers to as the
glass industry’s first and simplest response to improving thermal performance to reduce
energy consumption.

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The IGU is an example of an assembly, in this case comprised of at least two glass panes
separated by a spacer and sealants to create a hermetically sealed cavity between the glass
panes. The air cavity is largely responsible for the improved insulation value of the
product. Thermal and solar performance may be further enhanced through the addition of
specialty coatings on the glass surfaces and gas fills in the cavity. The IGU assembly is in
turn a component of a window or façade system with additional components.
The layered assemblies comprising buildings experience varying rates of aging (Brand
1994, 13). The assemblies are also made up of various components. These material
components may vary in their durability characteristics and service life. Kesik (2002,
307) discusses differential durability as consideration of the relative service life
characteristics of the components that comprise an assembly and the assemblies the
comprise a building’s systems, and points out that the service life of a system or assembly
may be determined by its weakest link. Simplistically, an assembly made up of two
components, one with a 10-year service life and another with a 6-year service life, yields
a service life for the assembly of 6 years, and results in wasted durability of 4 years in the
first component. Ideally, an assembly should be designed so that the service life of
components is in harmony. An assembly can be designed so that a component with a
lower service life can be easily replaced in a cycle that matches the service life of the
assembly. In the previous example, a service life of 5 years for the second component,
combined with a strategy for its easy removal and replacement, could prevent wasted
durability and reduce embodied impacts. The concept of wasted durability is diagrammed
in Figure 4.3.

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Considerations of differential durability complicate service life assessment, especially in
complex, multi-component assemblies. Careful analysis of the material behavior of
individual components, their relationship and interactions, as well as their maintenance
requirements, is the basis of durability planning. Such analysis is rare in building and
façade design, and has been largely ignored by green codes, standards and rating systems
(Meadows 2012; Kestner and Webster 2010, 10-12; Brand 1994, 112). The exception is
Canadian Standard S478-95 (2007) Guideline on Durability in Buildings (Canadian
Standards Association 1995). The Canadian version of LEED, (LEED Canada-NC 1.0)
includes a point related to durability involving the development and implementation of a
durability plan as part of the building program. The U.S. Green Building Council’s
LEED® for Homes Rating System integrates considerations of durability, but not with
the commercial rating systems like LEED for New Construction (LEED-NC). While
offering no points directly relating to durability, LEED v4, launched in the U.S. in 2013,
includes for the first time whole-building lifecycle assessment, with a possible 1-3 points.
A minimum building design service life of 60 years is stipulated, and the provision
requires compliance with International Standards Organization (ISO) 14044, providing
Figure 4.3: Differential aging characteristics between components of an assembly may result in
replacement of the assembly and the premature service termination of the remaining fit
components (Kesik 2002) (graphic adapted from Kesik (2002).

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requirements and guidelines for lifecycle assessment. Other relevant ISO standards
include ISO 13823:2008 General principles on the design of structures for durability (ISO
2008) and ISO 15686-1:2011 Buildings and constructed assets-Service life planning (ISO
2011).
The focus on durability tends to favor material degradation, but there are other factors
that impact service life addressed in following sections. Ultimately, differential durability
is about the variance between predicted and actual service life, recognition of the
significant embodied energy expenditures that can result, identification of the causal
forces that produce the variance, and the opportunity presented by balancing and
optimizing these forces. It is important to understand the reasons for premature service
life termination.
4.3.6 Why buildings (and their façade systems) fail: Predicted
versus actual service life
The reasons why actual service life may be less than predicted service life are important
considerations when determining design service life and in durability planning. These are
not limited to quality considerations of material, design, manufacture or installation, but
may also include important socio-cultural factors; the potential technical life of a building
is seldom realized, as functional buildings and façade systems are discarded for other
reasons (Cooper 2010, 9; Kesik 2002, 306).
Physical Deterioration
Durability is most commonly considered in the context of physical deterioration.
Durability in this respect is ultimately a material consideration. Physical durability is not
a fundamental attribute of a material, but the behavior of a given material in a specific
service environment over time. A building’s façade system is unique in its role as the
arbiter between the internal and external environments, and protecting those interior
components: structure, mechanical systems, and furnishings; from aging processes
accelerated by exposure to climatic elements of moisture, wind, and sun, while
simultaneously providing solar control, view and ventilation. Thus, the façade system
itself is, at least partially, exposed to these elements. Mostafavi and Leatherbarrow (1993,
4) refer to this process of aging on the “outer surface” of a building as weathering, noting
the inevitability of its effect on buildings and, in the absence of intervention in the form
of maintenance, retrofit and repair, the progression toward failure and “ruination.”

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If the building or system is deemed practically unrepairable, either physically or
economically, its service life has ended. If this occurs before the predicted service life of
the building or system, it represents premature performance failure. This can result from
design flaws, for example inappropriate material use that is incompatible with adjacent
materials, or materials that fail to harmonize with the durability properties of the other
materials that comprise a system. Inappropriate detailing that results in moisture exposure
where none should occur is not an uncommon cause of premature failure. Another causal
force can be unrecognized substandard quality in the original materials or assembly
occurring during the processes of extraction, fabrication, transport, or installation; a kind
of built-in failure mechanism. Paint application is an example: paint applied improperly
can lack appropriate adhesion with the substrate. If this is not identified and remedied
prior to installation, it can lead to premature failure of the coating system (Bull 1991, 30-
32). In the case of an exposed metal façade system installed on a high-rise building, this
represents a serious problem leading to costly repair, or even system replacement.
Unanticipated changes in the service environment may also result in accelerated
weathering that can limit service life. Examples include changed exterior environmental
conditions resulting from increased exposure to industrial pollutants, or changed interior
conditions resulting from the conversion of an office building to a laboratory facility.
A building is generally expected to satisfy performance requirements related to safety,
structural capacity, air and water tightness, operability, maintainability, repairability,
durability, and visual, acoustical and thermal comfort (Silva et al. 2016, 16; Straube and
Burnett 2005, 40). The building façade plays a key role in virtually all aspects these
requirements, and a dominant role in most. In fact, Silva et al. (2016, 16) includes
“obsolescence due to the building envelope” among the depreciative processes leading to
the end of building service life (Table 4.1).

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Shortcomings in any of these requirements hold the potential to drop performance below
acceptable thresholds of quality. It is apparent from Table 4.1 that durability exhibits
other dimensions beyond weathering and physical deterioration that can be examined as
aspects of the broad concept of obsolescence.
Obsolescence
The concept of obsolescence in buildings again parallels products and the notion put forth
earlier of buildings-as-products. Obsolescence has been the focus of much research in
marketing, the social sciences and industrial product development. Burns (2010, 41-43)
tracks the development of industrialized manufacturing processes in the early half of the
twentieth century to the emergence of the concept of planned obsolescence around
midcentury, which essentially shifted consumer focus from reliability and performance to
style, creating the foundation for the modern consumer society. This was accompanied by
a growing marketing emphasis on comfort and convenience, and the emergence of
disposable products and the “throwaway society” (Cooper 2005; Evans 2012). There was
a predominant popular perception of a growing prosperity provided by a world of infinite
resources. Durability was of limited consideration.
The throw-away economy seems alive and well. Americans generated 4.43 pounds of
waste material per person per day in 2010, equal to approximately 250 million tons of
municipal solid waste (MSW). While recycling improved from under 10% in 1980 to
34.1% in 2010, the per capita waste production increased from 3.66 to the 4.32 pounds
per day. (USEPA 2010, 1). This does not include waste generated by the construction
Table 4.1: Categories of threat to service life (from Silva et al. 2016, 16).
• physical deterioration
• economic obsolescence
• functional obsolescence
• technological obsolescence
• changes in social context
• obsolescence due to the building envelope
• legal obsolescence
• aesthetic obsolescence
• environmental obsolescence

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industry, called construction and demolition (C&D) waste. This added an estimated 130
million tons of debris to the solid waste stream (Falk and McKeever 2012), increasing to
166 million tons by 2014 for buildings alone (not counting roads, bridges and other)
(USEPA 2016, 15). It constitutes a major percentage of total solid waste in the U.S. and
worldwide, with most of it deposited in landfills (Rao et al. 2007, 71; Behera et al. 2014,
502).
In Future Shock, Tofler (1970, 56) links buildings to the emerging “culture of
impermanence,” referencing Miami apartment houses replaced after only ten years
because it was cheaper than modifying them. Not that buildings were generally perceived
in quite the same way as, say, disposable razors. They were not talked about as
“disposable buildings.” The thinking behind the buildings, however, may reflect the
influence of the time. Industrial processes were yielding new materials and technology
for the consideration of building designers at an escalating pace. The availability of
economical extruded aluminum profiles, and the development of the float glass process in
the 1960s, provided the primary materials needed for a new lightweight building cladding
technology called curtainwall. This converged with parallel developments in elevator,
HVAC, and steel framing technologies to enable the tall building boom of the 1960s and
‘70s that altered the skylines of many North American cities (Wigginton 1996, 94-6).
Most of these buildings are still standing, most with their original façade systems, many
badly in need of façade retrofit. Unfortunately, many of them may be determined
obsolete, and subject to demolition rather than renovation (Browning et al. 2013). The old
façade systems are at least partially responsible. Many are already technically obsolete,
providing substandard service quality and subjecting users to compromised interior
environments, but remain in service because of the cost and disruption associated with
renovation, typically requiring over-cladding or replacement.
Obsolescence is an umbrella term for the forces other than physical degradation that can
compromise service life. It is a key factor in the service life equation, and often the
determining factor of actual service life. Obsolescence surpasses physical degradation as
the leading cause of building demolition and major renovation (Henket 1996, 14;
Aikivuori 1999, 6-7; Kesik 2002, 312; Sarja 2005, 17). Comprehensive data is lacking,
but a limited survey by the Athena Institute (Trusty and Angeles 2005) of 227 buildings
demolished in Minnesota between 2999 and mid-2003 revealed that the most common
reasons for demolition had little to do with physical degradation, with area

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redevelopment responsible for 35%, and suitability of use 22%, together accounting for
the majority. Another 24% cited lack of maintenance, which suggests material
degradation, but together these results point to issues of adaptability and maintenance as
primary durability factors. Similar results were found in a survey of façade retrofit
(Martinez 2011; Martinez et al. 2015). In any case, it is clear there is more going on than
physical degradation.
The absence of a clear link between material degradation and building obsolescence
highlights the potential for wasted durability and unnecessary cost in using more durable
materials in new construction and renovation projects. A breakdown of the modes of
obsolescence relevant to buildings and their major systems is required to evaluate the
causal forces behind service life termination.
Allehaux and Tessier (2002, 127) postulate that functional obsolescence occurs when a
building or building system can no longer provide for its intended use and note causal
forces of change in the marketplace, technological advances, or initial design flaws.
Functional obsolescence is linked to user expectations (Silva et al. 2016, 17), (therefore, a
largely subjective phenomenon) and can be discussed in terms of fitness of purpose—that
is, functional appropriateness to business mode or strategy—and serviceability, or the
capacity of a facility to support user functions (Davis and Szigeti 1999, 1857). Sarja
(2005, 7) references functional obsolescence as the inability to satisfy changing
conditions of functional, economic, technological, cultural or ecological requirements.
Kesik (2002, 313) suggests other modes of obsolescence in referencing “locational”
obsolescence produced by market shifts and changing patterns of land value that can
result in “enormous expenditures of embodied energy.” Silva et al. (2016, 16) explicitly
list “obsolescence due to the building envelope” among an expanded list of obsolescence
modes. Sarja (2005, 19) adds ecological obsolescence as an appropriate additional mode
to consider, as the inability of a facility to support developing ecological requirements of
society relative to resource consumption, waste, and environmental degradation.
Burns (2010, 45) proposes four categories of obsolescence for products, but with
apparent relevance to buildings and their façade systems.
1. Aesthetic obsolescence: This is about appearance, of course; much of a building’s
appearance is determined by the façade. Aesthetic obsolescence comes in two
modes, one related to visible wear or, the other relating to style or fashion. The

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tall building boom starting in the 1960s replaced the dominant aesthetic of
masonry and punched-window facades of the time with a markedly new look.
Many of the Midcentury tall buildings in Midtown Manhattan were influenced by
the Modernist style characterized by grided orthogonal elevations, flat vertical
surfaces of glass and metal framing. Recent building aesthetics have trended
toward curved, geometrically complex surfaces. Façade retrofits may be more
driven by fashion than function, an expressed desire to “modernize” a building
(Martinez et al. 2015, 938).
2. Social obsolescence: Accelerating processes of urbanization and social change
hold the potential for significant changes to the way buildings are used. The rate
of social change presents challenges in attempting to anticipate how buildings
might be used through their lifespan. For example:
a. Costly and congested transportation systems may amplify a trend of
working at home, which could change the way office space is used.
b. The demand for plug requirements in office buildings due to the
increasing use of personal computing and communication devices was
largely unanticipated.
c. Public awareness of the health impact of the work environment and what
became known as sick building syndrome was behind many interior office
renovations, and led to changes in the practice of interior office design and
renovation.
d. Evolving zoning, codes and standards can create other forms of social
obsolescence.
3. Technological obsolescence: Rapid technological change can yield product
obsolescence. Architectural glass products are a good example in the building
sector. Single-glazed products are rarely used today and can be regarded as
obsolete, although single-glazed widows remain in many older buildings.
Contemporary glass products are double or triple-glazed, with transparent surface
coatings and a diversity of other features that improve thermal and solar
performance. The glass industry has a long history of introducing product
improvements on a frequent basis, products with the capability to provide
significant performance improvements in building comfort and energy
performance. Market uptake is hampered by the cost and disruption associated
with the adoption of these products through façade retrofit, at the expense of the
building occupant and the energy performance of the building sector. This
phenomenon can contribute to economic obsolescence.

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4. Economic obsolescence: Many of these suggested obsolescence modes may be
ultimately traced to economic factors. When repair, maintenance and renovation
activities are too expensive for the building owner to implement, the building,
system or component has become economically obsolete. Brand (1994, 80-6)
suggests an economic service life ending when building replacement represents a
more profitable solution, as similarly suggested by the Midcentury (un) Modern
report (Browning et al. 2013) as a current reality for many of the tall curtainwall
buildings constructed in the 1960s and 70s in Midtown Manhattan. There are
cases of building façade renovations where the cost of renovating the original
façade system exceeds the cost of replacement (see Javits case study in Section
8.5.6). This may be a form of what Allehaux and Tessier are referring to with
initial design flaws as a cause of functional obsolescence. If so, contemporary
curtainwall designs need to be scrutinized from this perspective. Silva (et al.
2016, 18) concludes that buildings become economically obsolete “naturally”
with the emergence of new and improved building technology, but Brand (1994,
72-87) makes the case of this as often a false economy.
In whatever manner these various modes of obsolescence are categorized, they are not
isolated in any given instance, but overlap and interact in complex ways that produce
outcomes challenging to anticipate. Obsolescence can result in significant wasted
durability as a causal force in reducing actual from predicted service life. Unfortunately,
most contemporary buildings are inadvertently prone to obsolescence by design, with
economic considerations as the root cause. Building budgets dominated by pursuit of the
lowest first cost, force design focus on initial conditions rather than on the following
decades of lifecycle use. Alexander (n.d.) says, “The money is wrong in most buildings,
and it’s crucial. There should be more in basic structure, less in finish, more in
maintenance and adaptation.” Indeed, these considerations of obsolescence reveal a direct
link with flexibility and adaptability in buildings and their façade systems.
4.3.7 Linkage to Adaptability
Obsolescence is a factor in differential durability as a comparison between a building’s
service life and its functional obsolescence, and is directly linked to adaptability Kesik
(2002, 307, 312, 402). Sir Richard Rogers is among the architects that understands the
importance of adaptability.
I believe that many architects misjudge the private needs of buildings. The rate
of change in society—and you can pick the computer or whatever you want as
a symbol—makes long term prediction impossible and inflexible building

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unreasonable. A set of offices today may be an art gallery tomorrow. A
perfume factory may switch to making electronics. What we can do—and this is
the key to much of my work—is to design buildings that allow for change, so
they can extend their useful lives...—Sir Richard Rogers (Caplan 1988)
Rogers accomplishes this with the Lloyd’s Building (1986, London, Richard Rogers
Partnership) by separating building services from useable space, making services easily
accessible, and designing so that services can be retrofit without building closure (Iselin
and Lemer 1993, 35-6). Disruption to ongoing building operations is a significant
problem with façade renovation, resulting from design practices that ignore the future
need for retrofit as discussed later in this article.
Buildings change over time, in response to the physical aging of materials, finishes and
systems, but especially in response to the changing needs and expectations of users
(Brand 1997, 2). The ability to accommodate such change may determine a buildings
survivability. Strain (2017, 6) calls for designs that anticipate future renovation with
systems and components that are easy to remove, clean and refurbish, as a strategy to
decrease the likelihood of building replacement. Sarja (2005) and Slaughter (2001)
reference the important aspect of adaptability, tying obsolescence to an inability to adapt
to changing functional, economic, and cultural conditions. Hartkopf and Loftness (1999,
385) articulate strategies to accommodate change and avoid obsolescence that involve
modular, expandable, and reconfigurable systems for all primary building functions and
services, noting that, “...dynamic reconfigurations of space and technology typical in
buildings today cannot be accommodated through the existing service infrastructure…”
Pialot and Millet (2014, 379-84) emphasize the priority of upgradability in product-
service systems. Upgradability is recognized here as a particularly relevant form of
adaptability, and certainly relevant to the façade systems for TCBs. The drivers of
obsolescence appear to be accelerating; adaptability is a way to prevent premature
obsolescence and make buildings more sustainable (Arge 2005, 127; Kincaid 2000, 155).
While obsolescence may cut short a building’s lifespan for reasons having nothing to do
with its design; e.g., urban redevelopment, poor construction or maintenance quality
(Athena Institute 2006, i); Khasreen et al. (2009, 677) note that, “The ease with which
changes can be made and the opportunity to minimize the environmental effects of
changes are partly functions of the original design.” That curtainwall systems are not

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designed to accommodate future retrofit represents a threat to the service life and quality
of both the façade system and the building.
Adaptability, along with such related considerations as repairability and maintainability,
include important cost and convenience factors. If the cost of maintaining, repairing or
adapting buildings or building systems is too high, or if the disruption to ongoing
building operations is too great, they are far more likely to be replaced, resulting in the
potential for premature termination of service life and resulting wasted durability. Kesik
(2002, 313) calls into question the value of the original design when costs for adaptive
reuse approach or exceed replacement cost. This is often the case with the curtainwall
façade systems. The façade retrofit of the Javits Convention Center and the United
Nations Secretariat Building in New York City provide prominent examples (4.4.7).
Curtainwall systems fail to anticipate the need for future retrofit (Patterson et al. 2012).
Iselin and Lemer (1993, 43) recommend oversizing the original shell construction to
accommodate future expansion and avoid obsolescence, an arguable practice given the
increase in embodied energy, but one that may make sense with large commercial
buildings. However, unlike many smaller residential and commercial buildings, tall
curtainwall buildings are seldom expanded, maintaining the original core and shell
throughout the building lifespan. The authors note that the suggested strategy conflicts
with the dominant focus on minimizing first cost, preventing consideration that could
extend service life and reduce lifecycle cost. There is opportunity in bringing special
attention to the shell—structural and envelope systems—with respect to obsolescence and
adaptability. Relatively small premiums in original construction costs can pay large
dividends over a building’s lifecycle. Oversizing the shell to accommodate future growth,
oversizing the structure to accommodate future vertical expansion, oversizing façade
anchorages in anticipation of code requirements trending more demanding, narrower
floor plates and higher floor-to-floor spans, are among the strategies that can make
buildings more adaptable and less prone to obsolescence.
Adaptability and durability are linked attributes of sustainability, and important
considerations of resilience (Patterson et al. 2016, 37-42). The importance of adaptability
increases with age. As buildings and major building systems are designed to extend
service life, they become more likely candidates for functional obsolescence.
Unanticipated major renovations, and even building demolition, can cut service life

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potential short, resulting in wasted durability and increased embodied impacts. Adaptive
capacity is a safeguard against such obsolescence, and an important attribute of
sustainability (Athena Institute 2006, i).
4.3.8 Climate Change, Complexity, and Innovation
Nireki (1995, 404) notes the challenge of service life prediction, or the determination of
an appropriate design service life, when novel systems and materials or unfamiliar
service environments are encountered. This raises the issues of climate change,
complexity and innovation.
Climate change is an emerging consideration bringing uncertainty to the assumption of
service environment when forecasting service life. The uncertainties of warming climate
challenge predictions of emerging service environment, but there is ample scientific
evidence linking climate change with increasing frequency and magnitude of extreme
weather events, as well as shifting patterns of rainfall (Bernstein et al. 2007), all of which
can lead to unpredicted damage and unanticipated repair requirements to materials and
assemblies.
The award-winning Svalbard Global Seed Vault, designed as a “failsafe” facility for the
storage and preservation of global seed stock, was opened in 2008 to widespread acclaim.
Buried in 120 meters of rock near the North Pole, the facility was designed to safeguard
against the threat of climate change. The vault was threatened and nearly breached by a
combination of ice melt and heavy rains in October 2016. Arctic temperatures were the
warmest every recorded that year. A spokesman for the Norwegian government, owner of
the vault, commented, “It was not in our plans to think that the permafrost would not be
there and that it would experience extreme weather like that.” (Aschim 2016) Repairs
were successfully made and improvements are planned, representing what the Athena
Institute would term “unforeseen costs or disruption for maintenance and repair,” but
certainly no reason to restart the service life clock. Unanticipated changes may be the
leading cause of obsolescence in buildings. The uncertainties of climate change
exacerbate this problem.
Complexity and customization tend to reduce regularity, modularity, and adaptability, as
well as resilience and sustainability. Simplicity is an attribute of sustainability. High-
performance buildings providing improved energy performance at the cost of significant

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additional complexity may be compromised as truly sustainable building solutions. These
considerations are highly relevant to the building façade, and are further discussed in
section 4.4.9.
Adaptability in buildings is linked with maintenance; the adaptive capacity of buildings
essentially becomes a maintenance attribute, as buildings are designed to be routinely
retrofit with new and improved technology, and periodically renovated to renew finishes
and materials subject to excessive wear.
4.3.9 Maintenance: The M-word
Building structural systems typically last the lifetime of a building without repair or
replacement. Building services and interior finishes are the biggest factors in recurring
embodied impacts (Cole and Kernan 1996, 317). Maximizing the potential durability of
the structural system must become a common goal. While building renovations are not
free and add to the embodied impact debt, renovations typically generate 50-70% less
emissions than new building construction (Strain 2017, 6). Maximizing potential building
service life, while minimizing recurring embodied impacts, requires designing and
planning for optimized repair, maintenance, retrofit and renovation over a building’s
lifecycle. Figure 4.4 illustrates the link between maintenance and service life, and
identifies that service life to be lost or gained through maintenance planning.

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Reducing embodied impacts is not simply a matter of material selection (Cole and
Kernan 1996, 317). As well-designed buildings with adaptive capacity achieve longer
service life, maintenance becomes critical. Maintenance can support the optimal service
life for an adaptive building, but maintenance alone cannot prevent obsolescence in a
building lacking adaptability. Maintenance complicates considerations of durability and
service life. The service life of virtually all materials can be extended by maintenance,
some significantly (Donca et al. 2007). Maintenance has a cost, however, both monetary
and in embodied impacts. Maintenance adds to the embodied GWP, bringing another
important consideration to material and system selection. The challenge is in determining
when the cost outweighs the benefit. The Athena Institute (2006, 4) defines the outer
limit of service life by the occurrence of “unforeseen costs or disruption for maintenance
or repair.” This is problematic in that it assumes appropriate maintenance and repair
planning as part of the building design. The absence of appropriate maintenance can force
major renovation, or even building demolition (Trusty 2005). Demolition is certain
termination of service life. The need to reset the service life clock in the face of major
renovation is debatable. The service life definition adopted here is identified as the time
period of actual service of a building or building system, including cycles of maintenance
Figure 4.4: Conceptual diagram of link between maintenance and service life (adapted from Iselin
and Lemer 1993, 16; Kesik 2002).

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and renovation, until the building is demolished or, in the case of a building system, it’s
replaced. Maintenance is a critical consideration regardless.
Mostafavi and Leatherbarrow (1993, 5) recognize maintenance as a process of renewal
involving both conservation and replacement, and note that the high cost of maintenance
has driven a pursuit of “maintenance-free” buildings. Maintenance has a negative image
(Takata et al. 2004, 643-44; Brand 1994, 110). Building owners regard maintenance as a
necessary evil at best, a cost center that depletes profits. Owners, architects, and even
façade specialists are naturally attracted to the mythology of the “zero-maintenance”
façade system, and some façade contractors cater to this myth by suggesting their
products as such (periodic cleaning excluded). This is understandable, especially when
the product in question may be hundreds of feet up the side of a building amidst dense
urban habitat. Contemporary high-performance curtainwall systems, when properly
manufactured and installed, are generally low maintenance enough that it becomes
tempting to rationalize considerations of maintenance as ignorable in the context of an
approximate 30-year design service life. However, with no durability plan and no
embedded capacity to accommodate future forces of deterioration and obsolescence, the
lifecycle outcome is unlikely to support sustainability goals for the building sector.
Zero-maintenance systems are not designed to be maintained and may not be
maintainable if service quality drops over time. The lack of maintainability and
adaptability reduces possibilities for upgrades and partial renovations, leaving
replacement as the only option. Replacement is an expensive and wasteful option, often
too expensive for a building owner to proceed, so obsolete systems remain in place,
subjecting building users to substandard indoor environmental conditions. It is this
practice that has produced the current tall building stock with aging facades for which
there is no remedy but to replace the façade systems in their entirety, a practice that
challenges principles of sustainability and eco-efficiency (DiSimone and Popoff 1995, 3-
7). Conditions of deterioration and obsolescence should first be addressed through
maintenance, then by remanufacturing aging product into new, with replacement as a last
resort. Planned repair procedures and cycles of maintenance and renovation can extend
service life (Donca et al. 2007, 215; Brand 1994, 110). Iselin and Lemer (1993, 21) refer
to this strategy for extending service life as rehabilitation or renewal. Consideration of the
feasibility of an ongoing process of renewal as a strategy to perpetuate service life

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presents an opportunity to enhance the sustainability of the built environment (Figure
4.4).
The link between maintenance and service life is obvious. Nireki (1996, 403) links
service life to maintenance and the prerequisite of a prescribed maintenance management
plan to the establishment of design service life. Daniotti (et al. 2008, 6) suggests the
expression of maintenance in terms of service life extension as potentially useful in
evaluating such factors as maintenance cost and convenience. Acknowledging the
potential for maintenance and retrofit processes to extend service life, Takata (et al. 2004,
643-44) proposes rethinking the old manufacturing paradigm of “how to produce
products most efficiently” to “how to avoid producing products” through closed-loop
processes that rely on the integration of lifecycle maintenance management. This
suggests the potential for transformation, even disruptive transformation, in the building
industry as providers shift from a product to a service focus, with maintenance as an
integral part of the service offering. A similar notion has been suggested by Nickol
(2016) as a challenge to the façade industry, in the form of façade suppliers leasing
façade systems to building owners for the lifetime of a building.
Researchers claim that obsolescence is inevitable (Burns 2010, 40; Aikivuori 1999, 3).
Especially with respect to large tall building projects and the massive commitment of

Figure 4.5: Cyclical renewals may extend service life by periodically elevating service quality
(Iselin and Lemur 1993, 22).

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resources they represent, every effort should be made to avoid this. The evolving
philosophy of lifecycle building design and maintenance planning suggests the potential
for system renewal as a closed-loop system; ongoing. This begins to support Brand’s
contention that “Every building is potentially immortal.” (Brand 1994, 111), and Wood’s
proposition that, “Buildings should last until we are done with them,” (Wood 2015).
Lifecycle maintenance concepts may provide the key to that immortality. Curtainwall
systems designed to accommodate planned repair procedures and cycles of maintenance
and renovation can extend the service life of the metal curtainwall system indefinitely.
4.3.10 Why buildings (and their facade systems) endure: All you need
is love!
Service life is dependent upon a number of factors, among them:
§ conceptual robustness and resilience
§ proper material use and design detailing
§ quality fabrication and installation
§ aesthetic appeal
§ economic viability
§ the integrity of the envelope (roof, walls, foundation), particularly in protecting
the structural system
§ maintenance (cycles of refit, retrofit, and renovation as required to maintain
minimum standards of service quality)
§ flexibility and adaptability to conditions of use
The built environment provides a complex, hybrid context combining architecture,
engineering, building science, aesthetics, social factors, and other influences. Ultimately,
the keys to endurance are adaptability and maintenance. Adaptability is the only
preventative measure against the threat of obsolescence, and even the most adaptive of
buildings will not last long in the absence of maintenance. Maintenance, retrofit and
renovation can compensate for poor initial design, fabrication, installation, and even
unanticipated damage from natural or manmade disaster. What endures is what gets
adapted and maintained over years and generations. What gets adapted and maintained is
what is loved and valued by people, neighborhoods, communities, cities and nations,
even if at considerable expense and sacrifice.

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The ambiguity of cultural change may prove as much of a challenge to anticipate as the
uncertainty of climate change. Climate scientists are at work in the modeling changing
weather patterns to predict climate data that may be used in building design today. Social
scientists are modeling social evolution in an attempt to predict what will be valued
tomorrow. Beauty plays a pivotal role in this value, whether as an absolute that survives
rapid social change or a relative perception subject to change over time (fashion). In this
sense, architecture that can shape a lasting perception of beauty among a population is a
powerful force for sustainable built environments. Buildings as “loved” objects that have
endured for centuries may provide clues to durability and the avoidance of obsolescence.
Sustainable development requires the building industry to deliver a product providing a
standard of quality, with a predicted service life including planned maintenance over the
building lifecycle that will not unnecessarily burden the many stakeholders of the built
environment. This necessitates two requirements: the establishment of an appropriate
design service life, and durability planning to support the lifecycle duration goal
established by the design service life.
4.3.11 Design Service Life Baselines for Buildings
When we build, let us think that we build forever. Let it not be for present
delight, nor for present use alone; let it be such work as our descendants will
thank us… - John Ruskin, 1875.
Every building is potentially immortal, but very few last half the life of a
human. – Stewart Brand, 1994.
Long building lifespans are achievable. The Pantheon, with the world’s largest
unreinforced concrete dome, has continuously served the people of Rome for nearly two
millennia. Contemporary curtainwall buildings are far less durable, and contemplating a
design service life measured in centuries seems unreasonable. The Pantheon was
originally a temple, now a church, and not an office or high-rise residential building.
How long buildings should be designed to last remains unclear. Intended use is one
among many factors to consider when establishing a building’s design service life (Table
4.2).

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When is the building not the building?
The Athena Institute recommends the CSA S478-95 definition for service life, “The
actual period of time during which the building or any of its components performs
without unforeseen costs or disruption for maintenance and repair.” The qualifier
“without unforeseen major repair or renovation,” is problematic but goes undiscussed.
This implies that such an occurrence would reset the service life clock for the building,
even though the building may endure in meaningful respects: location, structure, shape,
use, and even name, for example. Foresight is a recognized challenge. It requires skilled
intent, and a deliberate effort that has been discussed as often absent in building projects.
The current problem of retrofitting the facades of mid-twentieth century curtainwall
buildings can be viewed as a failure to anticipate the need for future façade renovation
(Patterson et al. 2012, 212-13). Even now, no large commercial curtainwall building has
yet been identified where major façade retrofit or replacement has been anticipated and
planned for (Patterson et al. 2012). Consequently, per the Athena Institute’s definition, an
over-clad or replacement of the curtainwall system resets the building service life clock.
The replacement of the curtainwall systems on the Lever House and U.N. Secretariat
buildings resets the service life clock, even though the entire structural systems remained
essentially unchanged. This seems appropriate given that these buildings ceased
operations and were vacated throughout a long renovation that stripped them to the
bones, emerging revitalized yet closely resembling the appearance at the beginning of
their initial service life. The service life restart seems questionable if the building were to
remain in continuous service throughout the renovation process. Based on the Athena
definition, a distinction can be made between service life and endurance, in that a
building can potentially endure through multiple service lives, even involving complete
restorations or reconstructions.
Consideration of embodied GWP makes clear the importance of service life. Yet,
durability planning and service life definition are rarely considered for buildings or
façade systems (Birschke 2005; Patterson 2014). Codes and standards seldom address
building service life, and professional opinion varies considerably on how long buildings
should last. Contextual considerations are important: intended building use, local
conditions, and projected development in the area among them. Multiple factors can limit
lifespan by rendering a building obsolete. Urban redevelopment may dictate the removal
of a building before the end of its service life. The related forces of accelerating social
change and urbanization combine to produce increasing uncertainty in future building

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needs. Comprehensive and anticipatory planning will not prevent all occurrences of
premature obsolescence. Yet the importance of mitigating embodied impacts rivals that
of operational energy consumption; commercial and multi-family residential buildings at
the scale of large urban high-rise structures represent a considerable investment of
resources—with the spectrum of accompanying environmental impacts.
It seems a reasonable objective to design and construct these buildings with enough
adaptability, resilience, and robustness to endure for a very long time. The Great
Recession of the early twenty-first century serves to as a reminder to the uncertainty of
future economic conditions, and that the funding for repeated cycles of building
renovation may not always be available when needed. Constructing buildings with an
expiration date burdens future generations with their replacement. At the least, the
potential for unfavorable economic conditions should be anticipated and options for
extending building service life considered. In addition, extending service life is a means
to reduce embodied GWP, and the definition of appropriate goals for design service life
representing optimized lifespans is key.
There are complexities that effect a building’s service life, the forms of obsolescence
among them (Section5.3.6). These same complexities confront the endeavor of
establishing appropriate baselines for service life. The difficulty is rooted in the
subjectivity and contextual considerations involved in establishing a minimum acceptable
level of performance in buildings and their major systems, which defy scientific methods
(Silva 2016, 48; Iselin and Lemer 1993, 17). Aikivuori (1999, 1375) found that even
building repairs were largely based on subjective criteria, with only 17% the result of
deterioration, with fully 44% resulting from subjective decision making, emphasizing that
largely subjective factors of obsolescence, and not physical degradation, determine
durability and service life.
There are many wide-ranging considerations in determining service life targets for
specific building including service environment, design, service quality, and different
forms of obsolescence (Table 4.2).

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Table 4.2: Factors in determining design service life (Athena Institute 2006, 9-16; Straube and
Burnett 2005, 37-42; ISO 2000).
service environment site conditions
climate and microclimate
intended use
indoor environment
design material quality
design and detailing quality
design complexity
unconventional design or material use
fabrication and installation quality
service quality minimum parameters
maintenance planning
social, technological, and
economic obsolescence
obsolescence and social factors
urban development plans & policies
changing needs
heritage value
adaptive capacity
lifecycle cost

There is no consensus on how long a building should last, even when variables of
typology, climate, site, and others are eliminated. Durability is a measure of service
performance in the context of its application over a given timespan; durability is
necessarily planned in the context of a defined service life. A window system designed
for a 20-year building is unlikely to be the same as one designed for a 100-year building.
Rau and Crawford (2015, 147) contend that service life definition and considerations—
including material selection, maintenance planning and repair strategies—must be
integrated into the design process to support sustainability goals in building construction.
Baselines for building service life could act as guidelines for building teams confronting
this issue, yet existing data, practice and opinion challenge convergence on building
service life baselines.
Iselin and Lemer (1993, 13) state that 15-30 years is a common design service life for
many building types. Crowther (1999, 3) suggests 40 years as “typical.” The Athena

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Institute (2006, iv) suggests a “conservative” estimate of building lifespan at 40 – 60
years. This is consistent with anecdotal evidence of 50 – 60 years as expressed by
building professionals when asked how long buildings should be designed to last. This is
an improvement over the apparent prevailing attitude in the 1960s, but still represents a
cultural bias that undervalues durability. Kestner and Webster (2010, 1) posit that a 50-
year lifespan is commonly assumed for commercial buildings (noting that many fail well
short of that mark for other reasons than deterioration). Khasreen (2009, 679-80)
references an LCA study that assumed a 75-year building lifespan, noting it as “…very
long compared to most other studies, which typically assume 50 years.” A summary of
several studies and opinions reveal a range of years with little convergence (Table 4.3).

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The Pacific Northwest National Laboratory (PNNL) for the Building Technologies
estimates the median lifespan of commercial buildings at 70 – 75 years (D&R
International, Ltd 2011). The lifecycle of large commercial and multi-family buildings is
considerably longer. Bohne (et al. 2015, 306) claim that, unlike consumer products,
Table 4.3: Summary of service life and design service life data and opinion from literature review.
reference building service life (years)
Iselin and Lemer (1993, 13) 15-30
Crowther (1999, 3) 40
Athena Institute (2006, iv) 40-60 (conservative)
informal polling 40-60 (“should last” speculation)
Kestner and Webster (2010, 1) 50
ASHRAE 189.1 (2014) 50 (minimum)
Khasreen (2009, 679-80) 50-75
PNNL (D&R International 2011) 70-75 median lifespan of commercial buildings
CSA S478-95 (2007, 7) 50-99 most buildings
100+ monumental and heritage buildings
Bohne (et al. 2015, 306) 100
Kesik and Saleff (2009) 250 foundation and structure (armature)
Christopher Alexander (from Brand 1994, 127) 300 for foundation and structure
(Mouzon 2016) 1000
Wood (2015) indefinitely (as long as wanted; tall buildings)
curtainwall system service life (years)
Brand (1994, 13) 20 (not curtainwall specific)
Richards (2015, 159) 20-30 year replacement cycle
Kim (2011, 3436-45) 20 glass; 40 frame
Mayer (2006) 25-35 (to major renovation: replace IGUs,
gaskets, frame caps)
(IBI 2000) 32-38 (average)
Dean (n.d.) 30-40 (anodized aluminum curtainwall)
informal polling 30-40 (“should last” speculation)
Meadows (2014, 51) 40 (how long it should last with proper
maintenance)
Zaborski (2017) 40 estimated
deJonge (1996, 8) 40 approx. expected
Cheung and Farnetani (2016, 39) 40-50 service life approx. limit
Kesik and Saleff (2009) 50 design service life (5 cycles to match
structure)
University of Washington (2015) 50 design service life

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buildings typically have a functional service life of over 100 years, but fails to
substantiate that claim. With large urban commercial buildings, however, this may be the
case. Relatively few tall buildings, for example, have been demolished. In August 2017,
the database of tall buildings (CTBUH 2017) maintained by the Council for Tall
Buildings and Urban Habitat included 262 buildings 50-meters or taller over 100 years
old. Approximately 80% of them were still standing.
Christopher Alexander (from Brand 1994, 127) champions long-lived buildings, and
differentiates between building systems, claiming that building foundation and primary
structural systems should be good for 300 years. Kesik (2002) also contends that the
structural systems of modern buildings are engineered to support a lifespan of several
hundred years as established by numerous precedents. Niche innovative builders like
master mason and timber framer Clay Chapman recognizing the value of extended
service life are exploring 1000-year building solutions (Mouzon 2016). Wood (2012;
2015) acknowledges that the service life of a tall building is an unknown, but argues that
these buildings should be designed to last forever, or “until we are done with them,”
suggesting a strategy that may be interpreted as one of perpetual renewal in which service
life can be extended indefinitely, a concept that runs counter to experience and is easily
dismissed by conventional thinking, but is further explored for its disruptive potential in
Section 4.4.
The design service life for the façade system also lacks consensus. Brand (1994, 13)
generalizes building skin changes on an approximate 20-yeaer cycle, driven by fashion,
technology, or the need for repair, but this is not expressly in the context of metal
curtainwall systems. Kim (2011, 3436-45) performs a comparative LCA using a service
life of 20 years for the IGU, and 40 years for the metal framing to match a 40-year
building service life. Kesik (2002, 6) cites a report (IBI 2000) on multi-unit residential
buildings in Canada that gives service life data for curtain walls at between 32-38 years,
with 35 years as average. Hartkopf and Loftness (1999, 390) stipulate an aspirational 50+
years for a building envelope system.
Extensive informal polling among façade professionals elicited responses of curtainwall
system service life expectations mostly in the 30-40-year range. This is perhaps
surprising, given that many of the curtainwalls constructed in the 1960s still exist and are
at least 47 years old at the time of this writing. While the service quality may be

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questionable, as it may have been at the moment of their completion, they have seen
continuous service. The problem with curtainwall systems is not their initial durability, it
is the challenge of their renewal; these systems are not maintenance or renovation
friendly. The structural systems are good for at least 100 years, and likely well beyond
that. The curtainwall system is another story. They are not designed to accommodate any
regime of maintenance or renovation, despite the evident need over a building’s potential
lifespan. The curtainwall systems are most often not renovated but replaced, at
considerable financial and embodied GWP cost, marking the end of the building service
life, and effectively resetting the clock on a new one. The question in the context of
curtainwall systems is: what are the potential benefits of anticipating and planning for
maintenance and renovation as a strategy for extending service life?
Summary of reasons for extending service life
Wood’s contention that buildings should “last forever—or until we are done with them,”
implies an embedded capacity to extend service life indefinitely. Clearly, there are many
factors that can end the service life of a building, some of them difficult to anticipate.
Therefore, systems should be as adaptable as possible to changing conditions and in the
worst case, accommodate disassembly and the reuse or recycling of all components.
There are also reasons why it may prove beneficial, at some future point in time, to have
the option of extending the service life of a building. A hedge against future economic
downturns would be one such reason.
The Woolworth building in lower Manhattan turned 100 years old in 2012 amidst a
renovation conversion of upper floors to luxury condominiums. Hopefully, many of the
tall buildings constructed in Manhattan in recent years will be in service at the turn of the
22nd century. There are some rather dire speculations and predictions about what market
conditions may be in that future (Goodell 2016). It is not hard to imagine time periods,
perhaps extended time periods between now and then, when financial resources are
scarce, and maybe unavailable for new construction, or even major renovations. Even in
today’s strong economic environment major façade renovations are being delayed for
reasons of cost. It would be nice to have the option to extend service life indefinitely with
incremental maintenance and partial renovations—activities strategically planned to
maintain a minimum acceptable service quality—that keep the building occupied, fully
functional, and in continuous use. The façade system is a primary building system
capable of realizing this potential. Again, adaptive capacity becomes an enabling

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attribute, along with the ease of maintenance, retrofit, and partial renovation activities as
needed to maintain service quality. Contemporary curtainwall technology does not
provide this option.
Given the many looming material scarcities as population grows and urbanization
progresses, combined with the environmental burdens of using those materials, it may be
that the construction of supertall and megatall buildings, or any large commercial
building projects, are one day relegated to past extravagance. For now, it seems
appropriate for society to demand that these materials are used optimally. An important
vehicle for doing this is to specify minimum service life baselines for all building projects
and require durability planning that integrates all major building systems. It seems that
society has evolved somewhat from the throwaway mentality of the mid-twentieth
century, but perhaps still has some way to go. The contention here is that building
lifespans should be generally considered in centuries. A modest start could be to require
all buildings to be designed to a 100-year baseline (some exceptions for temporary and
other buildings designed for a shorter service life). Required formal durability planning
could require explicit strategy for disassembly under conditions that justified an earlier
termination of service life, strategy that would include either the reuse or recycling of all
materials. Durability planning could also require explicit strategy for extending service
life indefinitely, or at least for the 300 years that Alexander recognizes as the appropriate
lifespan for foundation and primary structural systems. These simple, achievable
requirements could change building design and façade design, and enhance the
sustainability of the built environment. Chapter 5 uses the example of the IGU to
establish that adopting such constraints can drive innovation, potentially yielding novel
solutions.
With respect to tall buildings, Wood (2012) notes the challenges of demolition and
acknowledges that the building industry does not even know how to go about it,
contending that tall buildings should last indefinitely, and need to be designed that way.
The challenges particular to tall buildings, including their demolition are discussed in
Section 7.4.5: Is the TCB a sustainable building typology?
4.3.12 Service Life Planning
Durability science is inconsistently applied in the construction arts (Mora et al. 2011,
1469). Durability planning can help, as suggested by the practice of service life planning

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(SLP); essentially a planning process for managing lifecycle impacts for buildings and
their major systems. In addressing durability considerations of degradation and also,
importantly, obsolescence, SLP encourages durability, adaptability, reuse and
recyclability (Meadows 2012). Durability issues have been long neglected in building
construction, including green standards and rating systems, as discussed previously. That
has slowly changed. The Canadian Standards Association (1995) S478-95 specifically
addresses durability, and the Canadian LEED program was the first to include a point for
durability planning. USGBC LEED IV has incorporated a limited consideration of
durability. ISO 15686 is a series of standards, Buildings and constructed assets – Service
life planning, related to service life planning for buildings. The IgCC (2012) and
ASHRAE 189.1 (2014) have recently incorporated ISO 15686-6, Procedures for
considering environmental impacts. Adoption of these various standards remains slow.
Industry has pushed back on service life specifications, claiming that the standards and
guidelines are overly vague, and may represent implied warranties, a potential liability
for product and service providers (Ruth 2012, 25-26). SLP is intended to be an integral
part of building lifecycle planning, starting early in schematic design. It links to other key
project documents, like owner’s project requirements (OPR) and the architect’s basis of
design (BOD), and process like building information modeling (BIM). SLP supports
green building practices like building commissioning and integrated or whole building
design (Prowler 2017).
Yet service life planning is a critical sustainability issue (Meadows 2012). It calls for
matching the predicted durability of materials and systems employed with the design
service life of a building, thereby addressing the full building lifecycle. The level of
service quality may fall gradually but not fall below a minimum standard before the
design service life is realized. This reduces the potential for wasted durability (Kesik
2002, 5-12), while bringing maintenance issues to the forefront. Daniotti (et al. 2008, 8)
emphasizes the critical importance of detailed maintenance planning during early design
development. Meadows (2012) notes that building owners engage with some level of
durability considerations when initially assessing cost, how long the building and its
major components will last, and the maintenance and repair expenses involved over that
time. Adopting one of the standards for service life planning formalizes and elevates the
planning process, often involving a consultant. SLP involves assessment of the following
considerations for the building and all major systems and components (derived from
Meadows [2012]).

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§ initial cost
§ service life
§ functionality
§ obsolescence factors
§ assembly and installation requirements
§ reliability
§ maintenance and service requirements
§ repair and maintenance versus replacement cost analysis
§ robustness; likelihood of necessary repairs
§ resilience and risk analysis: consequences of failure
§ related operational costs (insurance, energy, inspections, etc.)
ASHRAE 189.1 includes requirements for a maintenance plan. While this requirement
does not specifically include the façade system, it does include mechanical and electrical
systems, so operable vents and automated shading systems would presumably be
included. It specifies a minimum 50-year building service life and also calls for the
provision of an SLP document, specifically referencing the building envelope, at
completion of design development. A copy goes to the owner for use during the building
lifecycle. The SLP must provide service life documentation for all assemblies, products
and materials that well require inspection, repair or replacement during the service life of
the building. Documentation is to include for each assembly and component that
comprises the building envelope system:
§ assembly description
§ materials or products
§ design or estimated service life in years
§ maintenance requirements
§ maintenance access for all components with and estimated service life less that
the building service life
The plan is intended to demonstrate that the specified service quality can be maintained
through the building service life, and what is involved in doing so.
SLP can effectively overcome the characteristic pattern of short-sighted decision making
in building design and construction resulting from a building owner’s awareness that

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ownership will be transferred before durability related issues arise. By adopting a
lifecycle context, SLP forces definition of design service life for a building, its major
systems, and all the materials that comprise the building, from foundation to finishes.
This definition in turn provides the context for necessary maintenance, repair and
replacement planning and procedures to support the specified service life. Equipment and
systems must be evaluated for maintenance access. Methods for system retrofit and
replacement must be established. End-of-life disposition must be determined, with an
emphasis on reuse and recycling.
There may be no more critical system for SLP than the building façade. In mediating
between the inside and outside environments, it is exposed to the strongest agents of
weathering and forces of degradation. At the same time, it protects all other building
systems, including the structural system from these same agents. In addition, the façade
defines much of a building’s visual character, already defined as a primary factor in
obsolescence. Façade service life planning (FSLP) as a component of SLP could
effectively do the following:
§ require definition of design service life for the façade system
§ reveal problems of differential durability between the façade system and building
service life
§ highlight differential durability problems between the various components that
comprise the façade system, e.g., between the architectural glass panels and the
framing system
§ expose access problems preventing inspection, repair and replacement of critical
weather seals
§ identify the challenges of retrofitting structurally glazed curtainwalls with high-
performance glazing upgrades
§ make clear the lack of options when it comes to system renovation that result in
replacement often being the most effective renovation method
§ reveal the cost and disruption, and accompanying risks, of future façade
renovation
This could bring change to the way curtainwall systems are designed and installed. SLP
and FSLP were nonexistent during the latter half of the twentieth century when the first
tall curtainwall buildings were constructed and have yielded a legacy problem of façade

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renovation that challenges sustainable building practices. Unfortunately, SLP and FSLP
are only rarely practiced today.
4.4 Material matters: Durability and embodied carbon
considerations
[Portions from this section were first published in Patterson et al. (2014).]
Metal-framed curtainwalls, like buildings, are specialized, complex assemblies that
challenge conventional notions of durability. There is no general consensus on how long
a typical curtainwall system should last. Most of the first-generation curtainwall buildings
still exist, with the earliest among them being some sixty years old and older. Most retain
their original curtainwall systems. Some few have been renovated. Many are in need of
renovation. There is some evidence that the service life of these early generation
curtainwall systems is in the 40-60-year range. This ignores the issue of a minimum
standard of serviceability; if current code standards for air and water vapor penetration
are applied, some of these systems may have been unserviceable from the beginning,
owing partially to the newness of the technology and the essentially experimental nature
of the early systems. There have been refinements over the decades that have
significantly improved performance; contemporary curtainwall systems are no longer
emergent or experimental, but the product of a highly developed technology of design
and delivery. Durability assessment of these systems has been limited.
Durability is a function of service life and service quality, considerations of high
relevance in façade systems, which uniquely combine attributes of both appearance and
performance, and bridge the indoor and outdoor environments. The actual performance
with respect to these attributes may not be equally apparent. One system appearing
aesthetically acceptable may be performing well below acceptable standards, yet remain
in use for a long time, compromising the operational energy efficiency of the building,
subjecting occupants to discomfort and compromising health, wellbeing and productivity.
Another system may be functioning to acceptable performance standards but suffer
evident visual deterioration that results in premature maintenance or repair, or even
replacement, and an accompanying waste and expenditure of embodied energy. Or a
system may become visually dated or otherwise inappropriate and suffer a similar fate.

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As discussed in section 4.3.6, it is these aesthetic considerations, not functional
performance, that characteristically drive façade renovation.
Two important distinctions about the evolution of curtainwall technology can be made.
First is the adoption of double-glazing—or insulating glass units (IGUs)—following the
first energy crisis in the early 1970s (de Jonge 1996, 7). Second is the advent of unit or
unitized systems, a strategy of modular prefabrication that enhances quality and
minimizes site labor, at the cost of considerable added system complexity. Unit systems
first appeared in the 1980s and grew to predominate new façade applications in the 1990s
(Brock 2005, 92). Today virtually all large-scale façade applications are unit systems.
The early-generation curtainwalls were called stick systems, referencing the practice of
processing lengths of aluminum extrusions on site, installing sequentially vertical
mullions to slab edges, horizontals between verticals, followed by the setting of glass and
other infill panels into the frames. The design, construction, and behavior under load of
stick and unit systems are substantially different, and there is little reason to assume that
their service life characteristics will have much in common (beyond material finish,
perhaps). In fact, contemporary unitized systems present certain challenges, discussed
later, that may render them less durable than their stick progenitors.
4.4.1 Low carbon material considerations
In addition to durability considerations in material selection is carbon intensity. Materials
possess varying levels of embodied carbon intensity. All aluminum, for example, is not
the same. Cheung and Farnetani (2016, 39) note that embodied carbon will vary as a
function of mining and processing locations, required transport, fuel types used in
extraction and processing, recycled content used to produce the billet, material finish, and
transport fuel consumption related to downstream fabrication processes of extrusion,
machining, and assembly, until the curtainwall units are ultimately delivered to the job
site and installed. They go on to discuss the impact of design choices on environmental
consequences, showing that careful specification and material procurement choices can
reduce embodied carbon in an aluminum frame by 54%, with additional potential
reductions if there is flexibility in material type other than aluminum. This is further
discussed in Section 4.4.9.

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4.4.2 Anchorage systems
Curtainwall systems are most commonly attached to the building structure at the floor
slab, either the top, bottom or face of slab, but can also be fixed at the face of beam or
column (Figure 4.6). Anchorages are typically comprised of two components, one fixed
to the building structure and the other bridging between the first and the curtainwall
system. The former essentially becomes part of the building structure, is often embedded
in concrete slab or welded to structural steel beam or column, and should be designed to
last the service life of the building, matching the capacity of the structural system.
Changing out this component is very difficult, costly, and sometimes not possible.
Cheong and Farnetani (2016, 40) reference a U.K. project where a high quality perfectly
serviceable stainless-steel curtainwall system was replaced because the galvanized fixing
component holding the system to the structure had corroded and needed replacing after
just short of 30 years from initial installation. This weakest link resulted in significant
wasted durability.
4.4.3 Framing Systems
Aluminum is the predominant framing
material in curtainwall systems. Aluminum
emerged as an affordable building material
in the mid twentieth century and was a
factor in enabling the rapid adoption of
curtainwall technology (Hunt 1958, 132).
The material was lightweight and possessed
wreathing properties considerably superior
to carbon steel, both attributes for a façade
application. Curtainwall framing systems
are typically of extruded aluminum. The
extrusion process facilitates the complex
member sections that accommodate gasket
raceways, screw splines, channels for water drainage, and other details of curtainwall unit
design. Extrusion dies are inexpensive, accommodating a high level of customization in
facade design. While the extrusion process is relatively inexpensive, the material itself is
relatively expensive as compared with steel, and with higher cost volatility (Burns 2011).
Aluminum and aluminum products are energy intensive in their processing and

Figure 4.6: Curtainwall anchored to column
face. Anchor design accommodates adjustment
in the x, y and z directions (courtesy of Enclos).

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manufacture, and consequently are recognized as high embodied energy materials, and an
important consideration for controlling embodied carbon. The carbon intensity range
between virgin and recycled aluminum can vary by a factor of 20 times (Cheung and
Farnetani 2017). Understanding the supply chain is critical to procurement. The
Aluminum Stewardship Initiative (ASI 2017), an industry advocacy group, claims that
recycled aluminum uses 5 percent of the energy and produces 5 percent of the emissions
of virgin material production. Like glass, aluminum is infinitely recyclable. The industry
expects significant growth over coming decades that will require the production of virgin
material. The carbon intensity of the virgin material will also vary as a function of the
fuel source used to produce the electricity for the smelting process, another supply chain
detail that can be controlled; smelting operations in some regions use electricity
generated with high percentages of coal.
The extrusions are machine processed, involving notching, drilling, and cutting, then
screwed together to build up the unit frames. Gaskets and insulation are added, then
opaque infill panels, and finally the units are glazed as required with vision or spandrel
glass panels. Glazings can be mechanically fixed to the frame, or simply glued to the
frame with structural silicone adhesives that also provide the weather seal (Figure 4.7).
Mechanical fixings are typically metal plates outside the glass pane that screw through
the joints between adjacent glass panels or between glass and frame, and are generally
concealed beneath a continuous cover plate along the panel perimeter. Mechanically
fixed glazings may use compression gasket weather seals instead of the bonding
adhesives.

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Figure 4.7: A 2-part silicone is applied between the fame and the IGU to bond the glass to the fame
and provide the weather seal.
There has been recent growing interest in wood as a potential alternative to aluminum
and steel in architectural applications. Wood is even being used as a framing material in
high-rise applications (Waugh et al. 2010). It is a feasible alternative to aluminum as a
curtainwall framing material, with potential for lowering embodied carbon. Cheung and
Farnetani (2016, 39) suggest a composite frame composition using wood as a primary
structural member for the curtainwall unit could reduce carbon intensity by 17 percent.
The use of wood in unitized curtainwall systems is unusual, but not unprecedented. The
Tower at PNC Plaza (2015, Pittsburgh, Gensler) utilizes wood as a primary structural
element in a highly customized double-skin façade system. Carbon savings from the use
of wood is not automatic. Supply chain complexities must be considered, along with end-
of-life disposal; if the wood is allowed to decompose in landfill the release of methane
mitigates the GWP benefit of its use.
4.4.4 Infill Panel Materials
The curtainwall framing systems support infill panels and fix the assemblies to the
building structure. Panels can be of various construction and materials including metals
and stone, and are often composite assemblies including insulation and plastics to
improve stiffness and thermal performance. Architectural glass in spandrel and vision
applications is the predominant curtainwall infill material, and is discussed in a flowing
section. The panels are sealed to the frames as part of the system air and water seal.

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Glass is the most common panel material in curtainwall systems, and takes two forms.
Vision glass is the transparent architectural products discussed following. Spandrel glass
is an opaque glass, generally used in the zone of the floor plate to conceal the slab edge
and below slab mechanical systems that are often concealed in this area. These areas can
involve complex constructs called shadowboxes (Figure 4-7), an aesthetic contrivance
intended to bring visual depth to the spandrel areas, reducing the visual contrast between
the vision and spandrel areas of the façade. Shadowbox panels generally incorporate
some form of insulation.

Figure 4.8: Section of shadow box at stack joint, with curtainwall anchor to building on right
(courtesy of Enclos).
4.4.5 Finishes
Finishes are always a predominant durability consideration, especially when they are
exposed to the elements as they are in façade systems. Bronze is a material that weathers
nicely, developing a rich patina over time. Mies van der Rohe used bronze extrusions and
panels on the Seagram Building in Manhattan (Lambert 2013,62-6), and the façade
system continues to appear serviceable. Alvar Aalto was another user of bronze sections
in his curtainwall designs (Ford ,125). While bronze weathers well, it is expensive and
less readily available than aluminum. Steel, in comparison, is seldom used in façade
applications because of its adverse weathering behavior. Bare metal exposed to the
elements quickly oxidizes to red rust. Steel was used in the Lever House façade, and
deterioration was a factor in the reconstruction of the façade system in 2001.

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Aluminum weathers far better than steel, but oxidizes to a dull white that is less than
aesthetically pleasing. For this reason, it is generally surface treated with an anodized
finish applied through a process of electrolysis or a painted finish. Many of the early
curtainwall systems were anodized, but this technique has been largely replaced in
exterior applications by modern high-performance fluoropolymer or polyester powder
coatings. Cheung and Farnetani (2016, 37) advise against anodizing, as powder coatings
are about 30 percent less carbon intensive, and is also less expensive to recycle. Exposed
finishes are a definite factor in curtainwall system degradation and an important
consideration when considering extended service life in the façade system.
Considerations of durability and carbon intensity must be balanced in a lifecycle context.
Powder coatings may be less carbon intensive that anodizing, but a shorter service life
may offset those carbon savings over the lifecycle of the anodizing. This must be
assessed. There are important interactions between materials and finishes that must be
considered also. Opaque powder coating processes provide for a reduced finish quality on
the aluminum extrusions, reducing carbon intensity, easing manufacturing requirements,
and reducing cost. Material selection is complex, and a critical aspect of the design
process.
4.4.6 Architectural Glass
Architectural glass is a ubiquitous material in the built environment, likely the most
common material in contemporary façade construction. The glass building, featuring high
WWR (window-to-wall ratio), has been embraced for a variety of reasons, despite the
familiar solar, thermal, and acoustical challenges they present. The early-generation
curtainwall buildings are the first of the type, and made use of single glazing: a single
pane of glass in the vision, and often the spandrel, areas. The glass was frequently body
tinted and sometimes mirror-coated to provide a measure of solar control. The body-
tinted and clear glass applications have generally aged without apparent effect, displaying
remarkably high service quality and indefinite service life (Meadows 2014, 52). Despite
the performance problems, the use of single-glazing is a prominent reason for the
durability of these early curtainwall systems.
The IGU, with its accompanying gas fill and plethora of coatings, was developed to
improve the thermal insulation properties of vision glass in the building skin. A perimeter
spacer, typically of aluminum, separates two glass panes, and the application of sealant

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creates a hermetically sealed cavity (Figure 4.9). Insulative gases like argon are often
employed to fill the cavity in place of air. The spacer is filled with a desiccant to
eliminate any residual moisture remaining in the cavity after fabrication. The functioning
of the perimeter seal determines the serviceability of the IGU. If this seal is
compromised, water vapor can enter the cavity and cause failure of the unit. Oxidation of
coatings applied to the interior glass surfaces, fogging, condensation, dirt and scum build
up, and even mold.

Figure 4.9: Typical insulating glass unit (IGU) construction. The wet sealant bonding of the space to
the glass to provide a hermetic seal, along with the coatings applied to the glass surfaces, reduce
the service life and compromise the recyclability of the glass material (Source: Advanced
Technology Studio – Enclos).
In practice, the service life of a curtainwall system may be determined by the service
quality of the IGU.

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4.4.7 Differential durability and metal curtainwall assemblies
As part of a comprehensive renovation program, the curtainwall system at the Javits
Convention Center in New York City was recently stripped from the structure and
replaced with a new system. The decision was made to replace the IGUs owing to their
age and physical appearance. Consideration was given to replacing the glass within the
existing curtainwall framing system, but was abandoned as impractical and too costly,
more expensive that a complete replacement of the curtainwall system (Golda 2014).
This decision allowed for a façade system redesign that resulted in a doubling of the
glazing grid module. This, combined with a higher light transmission glass specification,
resulted in a noticeable increase in façade transparency. (Figure 4.10) The façade was
originally completed in the mid 1980s, so had a lifespan of approximately 30 years, but
had been in obvious bad shape for years while renovation options and funding were
explored. This is consistent with the approximation of average curtainwall service life by
others (IBI Group 2000).

Figure 4.10: Javits Convention Center, New York City Pei Cobb Fried & Partners, 1986; FXFowle
Epstein renovation, 2014. During façade replacement: original curtainwall on left, new on right.
The durability of a system, from building to building product, is ultimately determined by
the service life of its least durable component (Kesik 2002, 306). It is clear that the

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curtainwall façade system plays a pivotal durability role in buildings, effecting both
considerations of performance and appearance, both primary causes of service life
termination. As a differential durability consideration, the façade system can potentially
be the weak link in determining a building’s durability, becoming unserviceable or
obsolete before the other major building systems. Meadows (2014, 51) notes the
reference life of a conventional glass and aluminum curtainwall system, assuming proper
maintenance, as 40 years (others find it less, Section 4.3.11), and as typically less than the
building design service life. Yet curtainwall systems are routinely designed with no
maintenance planning or provision for retrofit and renovation. Metal-framed curtainwall
systems are routinely installed on tall, supertall and increasingly, on megatall buildings in
dense urban environments; access to these systems for maintenance, repair and
renovation is a challenge. As with the Javits Center, when these projects are evaluated for
renovation options, replacement may be found to be the most, or only, viable solution. A
survey on façade retrofit (Martinez et al. 2015) revealed complete façade replacement as
the leading renovation strategy, ahead of incremental repair and replacement and over-
cladding options (See Section 8.6.4).
The cost and disruption of façade system replacement is significant. It requires the
relocation of occupants for at least a year, or expensive management and installation
logistics to keep the building operational throughout the construction process. This
process can lead to evaluating the replacement of the entire building as an option that
may present certain economic advantages, and leave the owner with a new building and a
complete reset of the service life clock, but with grave consequences in the form of
wasted durability and additional embodied impacts. From an embodied GWP standpoint
it is typically more “economical” to renovate an existing building than to replace it (Frey
et al. 2011).
As the façade system can be the weak link in whole-building durability, the IGU is a
candidate for weak link in the façade system (Jerome and Ayón 2014, 14), creating a
potential domino effect where the IGU could be contributory causal force in the
termination of a building’s service life. Deeper consideration of the IGU reveals some
interesting “differential” behavior between its component parts, and another level of
“weak link.” Richards (2015, 159) notes that the “failure of glazing seals is often the
thing that triggers the replacement of façade systems.”

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The service life of an IGU is a function of design, fabrication, and installation quality,
combined with service exposure, and varies widely. Typical commercial warranties range
from 5 to 10 years, but a predictable service life for an IGU is more difficult to define.
Designers and building owners need to know how long they can expect a product to
perform. A frequently referenced 25-year field correlation study (Lingnell & Spetz 2007)
examined three certified performance classes of IGUs under field conditions. The classes
certified through accelerated testing are established by specification ASTM
E774 “Standard Specification for the Classification of the Durability of Sealed Insulating
Glass Units,” defining classes C, CB, and CBA, with progressively improved quality
standards respectively. Classes C and CB exhibited a failure rate of 14% at 25 years of
service. With class CBA this failure rate is reduced to 3.6%. Note that with all classes
there is some earlier failure rate that accelerates over time. A large commercial or multi-
family residential project will typically involve thousands of IGUs embedded within the
curtainwall units. With the best product classification, test results indicate that 36 per
thousand will fail within 25 years. This could represent hundreds of failed units on a
large building. With the lower product classes, 200 per thousand can be expected to fail,
representing thousands of potential units. Unlike the curtainwall unit seals, failed IGUs
are highly visible from both inside and outside the building, and directly impact the
service quality of the curtainwall system. Industry continues to make improvements in
IGU durability—Cardinal IG (2016) claims key design and fabrication developments
over the years have produced a significant reduction in warranty claims for IGUs due to
seal failure. Still, quality remains an issue with the IGU; there will be seal failures, these
failed units will need to be replaced, and this should be considered as a planned repair
activity.
The clear or body-tinted single-glazing used in the first-generation curtainwall systems is
employed as a primary component—no subcomponents—in the curtainwall system, and
has a service life limited only by damage imposed on the material, in this case, breakage.
In the absence of such damage the material has an unlimited lifespan that can justifiably
be measured in hundreds of years. In comparison, the glass as a subcomponent in the
IGU (itself a subcomponent of the unitized curtainwall system), has a service life
measured in a few decades. The serviceability of the hermetic seal is the weakest
component in the IGU assembly. The effect is to collapse the predicted service life of the
glass subcomponent of the IGU assembly from virtually unlimited to 20-25 years. Mayer

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(2006) calls for a major façade renovation every 25-35 years to include replacement of
IGUs, gaskets, and frame caps as required.
The eventual outcome with the IGU is replacement, resulting in wasted durability and
embodied GWP of the glass material, the unintended consequence of improving
the thermal and solar performance of glass in the building skin. To further exacerbate the
problem, architectural glass is not recycled (Patterson 2011c), so the material is either
down-cycled for use as asphalt fill or concrete additive (Browning et al. 2013, Appendix
G), or more commonly, enters the solid waste stream and ends its lifespan at a landfill, as
with the replaced glass for the Javits Center (Berger. 2014). While pre-consumer glass is
typically recycled, easing the energy burden of new float glass production, no
infrastructure exists for returning glass to the manufacturers for recycling. Manufacturers
are also reluctant to introduce recycled products into the float line for fear of
contamination (Arbab 2011), which can be catastrophic to an operation designed to
produce continuously for 10-15 years. Such are the unintended and unarticulated results
of improving the thermal and solar performance of glass as a façade material.
Nonetheless, IGU’s have become the standard, and spectrally selective coatings the go-to
solution for improving solar, and to a lesser extent thermal, performance. The use of raw
float glass has virtually disappeared in the building skin (Bell 2009).
Widespread IGU failure leaves the building owner with an unpleasant choice of decision:
1. Keep the IGUs in service, compromising service quality of the façade system,
perhaps in both appearance and performance. Delay is tempting, but could expose
building occupants to an extended period of substandard service quality.
2. Replace the IGUs with new ones. This presents various challenges. Access can be
challenging in tall buildings in urban areas. In newer unitized systems, the glass is
often structurally glazed and bonded into the unit module. Removing the glass
involves cutting through the silicone bond, and reglazing the new IGU in place, a
sensitive process that does not benefit from the vagaries of field conditions. In
addition, IGU products are now available in so many variations of body tint and
coatings that the original product may not even be available, leaving the problem
of trying to match the existing product with the new one. Even if the original
product is available, it may not match the existing product, which has aged in
place and may have changed in appearance over time. The appearance of glass is
highly sensitive to subtle variations in color and transparency.

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3. If the IGU failures are widespread, a major renovation may be considered. As it is
often economically inefficient to limit this to retrofitting just the IGUs,
curtainwall renovations often involve over-cladding or replacement of the existing
façade system. The failure to anticipate this eventuality in the original system
design leaves few renovation options, all of which are costly and disruptive.
Implementing a major façade renovation subjects occupants to relocation or a
period of disruption, often a year or more, during the construction phase of the
renovation.
4. In some circumstances, the cost and disruption of a major renovation may not
make economic sense, and consideration may be given to replacing the building.
The scale will swing in the direction of building replacement if the desired
renovation includes the replacement of the curtainwall façade.
Choices 3 and 4 above can lead to even larger embodied GWP losses. Building
renovation versus replacement is part of the evaluation as building owners and developers
consider existing properties. Preservationists and sustainability leaders argue for
renovation, claiming renovation as the green alternative in most cases to building
replacement (Adlerstein 2016; Trabucco and Fava 2013, 38-43; Elefante 2007). Frey et
al. (2011, 84) used an LCA methodology to investigate building renovation versus new
construction over a 75-year service life in a wide range of building types and locations,
and found immediate embodied GWP savings in nearly every case. The Mid Century
(Un) Modern report (Browning 2013) argues that financial analysis may favor
replacement over renovation for many early curtainwall buildings in New York City.
Predominant among the reasons cited is the expense and disruption of façade renovation.
As these older early-generation curtainwall buildings are evaluated as candidates for
renovation or replacement, the cost and disruption of façade retrofit can become the
determining factor.
Table 4.4 shows baseline material content of a typical unitized curtainwall on a unit basis.
The other predominant material in curtainwall unit construction is aluminum. Extruded
aluminum is typically used to build up the frames for the modular units. While glass in a
typical curtainwall unit is approximately three times the weight of the aluminum frame,
the aluminum is responsible for nearly twice the embodied energy of the glass (Table
4.5). Together, the glass and aluminum represent approximately 88% of the combined
embodied energy of a typical curtainwall system (see Table 4.5 and Figure 4.11). Like
glass, aluminum is a material with a characteristically long lifespan, and is often used for
its durability in most service environments, making it a fit material for application in the

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building skin. The U.S. National Park Service (n.d.) lists the decomposition of glass in
the environment at 1 million years, and an aluminum can as 200 years. The service life of
aluminum in metal-framed curtainwall applications is generally determined by an
aesthetic attribute of service quality represented by the material finish as a subcomponent
of the framing system. While high-performance anodized or fluoropolymer coatings are
typically employed, they are subject to degradation over time as a function of
environmental exposure. Optimally protected, repaired and maintained, the base
aluminum is highly durable, with a service life measured in decades, if not centuries. The
finish, however, is closer to the service life of the IGU, in the 15 to 40-year range
depending on type (Mayer 2006; Dean n.d.), and subject to unacceptable levels of visual
deterioration depending upon the minimum quality standards defined for the system.
Gaskets are of at least equal concern. The challenge of differential durability is illustrated
in Table 4.5 by the divergent service life expectations of the various components.

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Table 4.4: Baseline material analysis of CW system (Source: James Casper).
CW Unit Component Weight QTY UNIT
Dimensions Unit Width 5 ft
Unit Height 12 ft
Densities Glass 156 pcf
Alum 170 pcf
Steel 490 pcf
Silicone 85.696 pcf
Insulation - Firespan 90 8 pcf
Aluminum Vertical Mullion Area (M+F) 5 in
2

Horizontals (Stack Joint + Int) 10.79 in
2

Lift Lug 30.6 in
3

Anchor Brackets 65 in
3

Hardware #14-14 Weight 0.04 lbf/ea
#14-14 QTY 24
1/2" - 13 Weight 1 lbf/ea
1/2" - 13 QTY 6
Shadowbox Height 3 ft
Aluminum Thickness 0.125 in
Steel Backpan Thickness 0.036 in
Insulation Thickness 4 in
Glass Inboard Lite 0.25 in
Outboard Lite 0.25 in
Spacer / Secondary Silicone 0.25 psf
Gaskets Bed Gasket 0.089 in
2

Air Seal (Vert) 0.055 in
2

Rain Screen (Vert) 0.051 in
2

Air Seal (Horz) 0.043 in
2

Rain Screen (Horz) 0.14 in
2

Structural Silicone (all) 5/8 x 1/4 0.15625 in
2

Summary Insulating Glass Units 6.75 psf
Frame 2.24 psf
Lift Lug and Anchor 0.16 psf
Fasteners 0.12 psf
Shadowbox - Alum Panel 0.44 psf
Insulation 0.67 psf
Backpan - Galv Steel 0.37 psf
Bed Gasket 0.04 psf
Air Seal (Vert) 0.02 psf
Rain Screen (Vert) 0.02 psf
Air Seal (Horz) 0.02 psf
Rain Screen (Horz) 0.06 psf
Structural Silicone (all) 5/8 x 1/4 0.07 psf
Total System Weight 10.97 psf
Notes no thermal breaks
shadowbox construction

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Note that the lifecycle inventory (LCI) data included in Table 4.5 as the “embodied
energy coefficient” from the ICE database (Hammond and Jones 2011) is intended only
to provide a relative measure of embodied energy intensity between the basic components
that make up a square foot of a “typical” curtainwall system. LCI data is location
dependent, with values varying as a function of regional fuel sources, transportation
practices, and other relevant factors. In addition, large curtainwall assemblies are often
highly customized, which could significantly impact the distribution of the energy use
intensity. What is common among most customized curtainwall designs, however, is a
predominance of glass and aluminum.
Table 4.5: Embodied energy approximation of baseline CW system using ICE LCI data (Hammond
and Jones 2011), with predicted service life averages.
CW Unit Makeup
Embodied Energy
Coefficient (kBtu/lb)
Weight
(lb/sqft)
Embodied Energy
Use Intensity
(kBtu/sqft)
Average
Service
Life (years)
Insulating Glass Units
10.73 6.75 72.43 20-25
2

Aluminum Framing
66.21 2.24 148.45 60-200
3

Lift Lug and Anchor 66.21 0.16 10.38 60-200
Fasteners 24.38 0.12 2.83
Shadowbox - Alum Panel 66.21 0.44 29.31 60-200
Insulation 9.18 0.67 6.12
Backpan - Galv Steel 12.25 0.37 4.50
Gaskets & Seals
26.51 0.23 6.10
10-20 (Meadows 2014,
55)
Totals 10.97 280.11

2
The raw float glass, the dominant component, has an indefinite service life.
3
Aluminum finish is the weak link: anodizing 30+ years; polyester powder 15-25 years; PVDF or PVF2 20+ years
(Mayer 2006).

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Figure 4.11: Analysis of embodied energy use intensity of primary CW assemblies indicating how
minority materials—gaskets, seals, finishes—compromise service life of majority materials—
aluminum, glass—which represent the large majority of embodied GWP of the assemblies.

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As with the glass, there is a significant collapse in potential service life of the aluminum
resulting from the lower component service life of either the aluminum finish or the IGU,
again producing durability waste (Figure 4.11). The aluminum framing system also
incorporates gaskets, quite small in section area and representing approximately 1% of
the weight of a typical curtainwall unit (Table 4.4), upon which the important
performance attributes of air and vapor permeability are largely dependent. The long-
term performance of a curtainwall system is largely dependent upon the quality of the
seals that provide the air and moisture barrier (O’Brien and Horschig 1991, 73). Brock
(2005, 14) notes that these important seals represent a fraction of the cost of a curtainwall
system, but their failure can be extremely expensive, with repair or upgrade very costly
and often not possible. Figure 4.12 shows workers installing gaskets into assembled
frames. The gaskets, sealants and finishes largely determine system performance and, as
the weak links, limit the curtainwall system durability (Cheung and Farnetani 2016, 39).
These minority materials are responsible for the service life collapse of the highly durable
majority materials, as clearly shown in Figure 4.11.

Figure 4.12: Curtainwall unit frames are factory assembled from fabricated aluminum extrusions and
gaskets fitted to extruded raceways (author’s photo).

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As the seal is a subcomponent of the IGU, the IGU is a subcomponent of the curtainwall
system, and the IGU seal thereby vies with the curtainwall unit seals for the shortest
service life, thereby defining the service life of the curtainwall system itself. The IGU is
the more likely culprit in limiting service life as a form of aesthetic obsolescence because
of its visibility, whereas substandard performance resulting from the curtainwall unit
seals is often masked, although potentially having more impact on energy consumption
and greenhouse gas emissions.
The design goal with respect to material selection and the minimization of embodied
impacts should be to maximize the durability potential of all the materials that comprise
an assembly. Conventional curtainwall systems fail to accomplish this, falling far short of
the durability potential of both the aluminum and glass. Simplistically, if the gaskets,
sealants and finishes could be easily renewed cyclically as needed, the service life of the
curtainwall system could be extended, harvesting more of the durability potential of the
aluminum and glass. The next section explores renewal strategies for the possibility of
extending the service life of metal-framed curtainwall systems.
4.4.8 Regenerative façade systems: Maintenance, repair and
renovation considerations
Haagenrud (2004, 2-1), Kesik (2002, 305-17), Brand (1994, 110-31) and others claim
that poor maintenance planning and practice accelerates the decline of building
performance, resulting in premature service life termination and wasted durability.
Haagenrud notes the built environment represents greater than half of real capital in
developed countries, and blames the “build and let decay” age of the past 30 years for the
current deteriorated state of the building stock. The “build and let decay” age is
synonymous with throwaway society explored by Cooper (2010) in Longer Lasting
Products: Alternatives to the Throwaway Society, and directly linked to the durability and
adaptability of metal curtainwall technology by Browning et al. (2013) in Midcentury
(Un) Modern. Haagenrud concludes that “damages to building materials and
constructions have become an enormous economic, cultural and environmental problem.”
Clearly, the durability of buildings is a major sustainability issue (even without the
consideration of operational energy consumption).
New design techniques and building technology have done much to enable reductions to
operational energy consumption (Lee et al. 2002), in the process unveiling the

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considerable problem of materials and their embodied energy and environmental impacts.
Extending the service life of buildings and their major systems provides a direct and
potentially efficient way to mitigate these embodied impacts. With respect to consumer
products, Cooper (2010, 8) states that, “Deliberate effort needs to be made to utilize fully
a product’s potential life-span, through careful use, regular maintenance, repair,
reconditioning (e.g. upgrading) and reuse of functional items (rather than disposal). The
same is true of the 5.6 million plus commercial buildings in the U.S. (CBECS 2012). The
building stock represents a significant asset of any nation, and must be protected as a
sustainable development practice. Complimentary to the monetary value, buildings are a
significant part of a nation’s cultural heritage requiring preservation for future
generations (Nireki 1996, 405). A large commercial building project represents an
enormous commitment of resources. It is imperative that an appropriate design service
life be established for any commercial building, and that strategies of use, maintenance,
renovation, and adaptability be developed and implemented to optimize the potential for
realizing the design service life. The building façade system must be similarly
considered, and designed to harmonize with the design service life of the building. This
necessitates the anticipation of maintenance, repair, retrofit, renovation, and
reconfiguration in the design of the façade system.
Opportunity lies in a facade system design that fully realizes the durability of its
dominant materials: glass and aluminum. One strategy to achieve this is the planned
maintenance of the seals, finishes, and other minority materials that have been identified
to compromise system facade system service life. This would require a significant change
in system design, and in the zero-maintenance design mentality, something that can only
be achieved through a clear demonstration of value. There are some problems with this.
Vulnerabilities
An obvious vulnerability of the unitized systems is the gaskets that provide the air and
moisture barrier. Figure 4.13 is a typical horizontal (stack) joint detail between
curtainwall units, showing the vertical penetration of the continuous fin of the lower unit
frame into a channel of the upper unit frame. (Details vary between manufacturers, but
the interlocking between units is typical.) The gaskets on each side at the top of the fin (in
yellow) act in compression to provide the air and vapor barrier, even as the units move
relative to each other and the fin slides up and down in the channel. The ability to
accommodate large movements between the units is one of the performance strengths of

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unitized curtainwall systems, particularly in enabling the construction of tall slender
buildings.

Figure 4.13: Typical horizontal stack joint between vertical curtainwall units showing location of
primary seal (Source: Advanced Technology Studio – Enclos).
The performance of the system relative to the important criteria of air and moisture
penetration is highly dependent upon the functioning of these seals. Yet once the unitized
systems are installed, these seals are entirely concealed and impossible to inspect or
service. There is no data on how long they maintain a consistent level of performance, or
at what rate their performance deteriorates and the patterns of that deterioration. There is
a lack of quantitative performance data collected from curtainwall systems as they age.
While most major new building construction projects undergo a program of performance
testing on façade mockups, very few require post-installation testing of the as-built
façade, so it is difficult to reliably establish even initial performance on a generalized
basis. Gathering performance data on existing curtainwall systems at various stages of
service life is an opportunity for future work.
Other vulnerabilities of contemporary curtainwall practices include the way the IGU is
mounted, essentially bonded, within the unitized assembly, making upgrades to the
glazing panels challenging at best, and often impractical. The systems are not designed to
accommodate such upgrades in spite of the fact that the lifespan of an IGU is 20-25

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years, less than the 35-50-year perceived service life of the curtainwall system (Table
4.3). Similarly, the curtainwall systems themselves are not designed in anticipation of
their eventual renovation, regardless of the service life of the façade system being
generally recognized as shorter than that of a building (Table 4.3). These practices
ultimately result in eventual periods of substandard service quality while renovation
options are assessed and found to be limited, followed by costly and disruptive
renovations that add significantly to the embodied carbon debt of an existing building.
The renovation challenge posed by the vintage body of mid-century TCBs is the subject
of Chapter 7. These vulnerabilities are design problems with solutions found in
anticipating and responding to these future requirements, including embracing
maintenance as a strategy to extend service life, minimizing embodied carbon and wasted
durability.
Debunking the zero-maintenance mythology
Curtainwalls are deliberately designed as zero-maintenance systems; they are not
designed to be maintained or renovated. The interlocking of the units prevents removal of
a single unit without disturbing neighboring units, rendering inspection of these seals
after installation of the curtainwall system highly impractical, and then only on a
localized basis with significant difficulty and damage to the assembly. This makes
repairs, maintenance, and any variation of renovation difficult, if not impossible (Cheung
and Farnetani 2016, 40). Fabrication and installation are critical factors in curtainwall
performance. The gaskets are exposed and vulnerable to damage during fabrication,
handling, shipping and installation processes. Without blower-door testing there is no
way to verify that initial system performance meets specifications. Such verification is
uncommon. The quantification of unrealized energy savings resulting from substandard
initial performance is an unfortunate unknown. Sophisticated building owners are
beginning to incorporate commissioning programs into their building projects, including
commissioning of the façade system (WBDG 2016). This is critical as façade systems
become increasingly integrated, incorporating automated shading systems, sensors and
controllers, and integration with HVAC through the building management system.
The lack of maintenance planning for the curtainwall façade system (beyond annual
cleaning) has potential implications for operational energy consumption, occupant health
and comfort, degradation of interior finishes and even the structural system, and
ultimately, façade system service life. Planned repair, maintenance and retrofitting

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procedures, and designs to accommodate them, present some advantages worthy of
consideration.
Simplistically, the service life of the aluminum framing can conceivably be increased by
the periodic application of a new finish. This is no easy task. Field applied finishes are
costlier and of lesser quality than those applied under factory controlled conditions,
especially at the elevations characteristic of urban towers, where just accessing the work
area can be a challenge. The systems, however, could conceivably be redesigned to
facilitate this process. A renovation cycle could involve the removal of an exterior cover
plate from inside the building, and the attachment of a new factory-finished plate, leaving
the rest of the façade system intact. A system could be designed with this cover plate as
the only material exposed to the elements other than glass. Or an opaque spandrel panel
could be similarly designed and managed. The replaced pieces could then be recoated
under factory-controlled conditions and reused. Alternatively, the façade system could be
designed with replaceable components accommodating an installation process accessing
the façade from an exterior window-washing rig.
The industry is working on improving the service life of the product, but the challenge
presented by the IGU would not be so bad if the curtainwall system was designed to
facilitate the change out of the IGU. It is not practical, and often not even possible, to
change out the IGUs in an entire curtainwall system. Instead, the systems are typically
demolished and new ones installed, with the resulting durability waste discussed above.
Today’s curtainwall systems are being designed and constructed with no consideration to
their future retrofit and renovation, this in spite of the fact that the IGU and curtainwall
system will not match the lifespan of the structural system, and ignoring the likelihood of
future product developments with higher performance. The many tall buildings recently
built or currently under construction will require façade retrofits to meet the carbon goals
established by the 2030 Challenge and other organizations, and yet there is no provision
to accommodate this requirement.
A cassette glazing strategy provides a solution: a minimally framed IGU with the frame
facilitating a compression fit into the curtainwall unit—that would expedite the change
out of a cassette panel with a new one, again from inside the building, something that
could be easily accomplished in the evening to prevent disruption to daytime office
operations. This could be part of the maintenance planning discussed in section 4.3.9 and

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4.3.12, planning that takes place in parallel with design development, such that the façade
system design facilitates repair, maintenance and retrofitting procedures. A repair
procedure could address the replacement of a failed IGU on an as-needed basis. A
system-wide upgrade could be planned every 20-25 years.
The issue with the seals between the modular curtainwall units is more challenging; a
curtainwall system designed to facilitate the easy removal of the gaskets for inspection
and replacement on a planned cycle, perhaps to match the replacement cycle of the IGUs.
The units are typically large and trending larger; larger units means fewer units meaning
less material handling and fewer units to install to enclose a building. If unit removal
proves impractical, perhaps the seals could be designed in the form of a removable
cartridge between units. The constraint of having an inspectable replaceable seal could
potentially drive the development of an entirely new façade system design. (The adoption
of equivalent constraints with respect to the IGU is explored in Chapter 5, through the
development of a conceptual solution.)
Much of the problem lies in the predominant use of bonded assemblies; the glass plies are
bonded together in and IGU; the glazing and panel materials are often bonded to the
curtainwall unit frame. High performance silicone sealants are frequently used to bond
glass to buildings without mechanical attachments, a practice called structural glazing. As
a consequence of the bonding practices, the assemblies cannot be disassembled for
inspection or maintenance. Bonding is not suitable for assemblies intended for long
service life.
The possibility of solving these problems without additional monetary cost may be the
biggest barrier to industry consideration, and these concepts may be deemed impractical.
However, “practical” solutions to the sustainability problem represented by the built
environment are increasingly challenging. As with building energy retrofits, the low-
hanging fruit of lighting and HVAC upgrades have largely been harvested; further
improvements, much needed, will likely involve some incremental cost. A question posed
at a recent façade conference broached this: “Can we afford sustainability?” A negative
response to this question presents a disturbing prospect. Metal-framed curtainwall
solutions can enhance attributes of sustainability, affordability is a separate issue.
There is, however, also the near certainty of additional cost in the form of embodied
impacts, as cassette systems, cartridges and other design features add to the material

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requirements of the façade system. Design must be guided by a careful selection of
materials, their optimized minimal configuration, combined with details that provide for
ease of repair, maintenance and retrofitting.
Façade Music
Sustainability is a design problem. By harmonizing (Kesik 2002) the service life
relationships between the various subcomponents that comprise a system, durability can
be optimized and embodied impacts minimized. Periodic maintenance and perhaps three
planned façade retrofitting cycles could support a building service life of 100 years. The
100-year building service life is ambitious by today’s standards, but is questionable from
a sustainability perspective, especially for tall and large buildings. If they are to be
sustainable, it is likely that buildings will need to support longer design service life
aspirations. Considerations of sustainability and resilience suggest the benefit of at least
embedding the potential for longer building service life in the building enclosure. The
prospect of stripping off the façade system on a recurring basis is impractical and
undesirable and does not support sustainable building practice. The structural systems
today should support a 300-year service life, and perhaps longer. If the structural system
is well-protected and incidental damage repaired as required, and the aluminum in the
façade system treated similarly, even longer service lifespans are certainly conceivable.
The prospect is one of achieving a steady-state with the façade system, where planned
repair, maintenance, retrofitting and partial renovation cycles keep façade system
performance above defined minimum service quality standards indefinitely. Virtually
every eventuality is accounted for, with all components repairable, maintainable, and
replaceable on an as-needed basis. If the building service life is extended long enough, it
is conceivable that no original component remains in the façade system, having been
replaced while the building remained in continuous service. A strategy of façade renewal
that includes harmonized cycles of maintenance and renovation suggests the potential for
radically extend service life. Such a strategy could maximize the service life of every
subcomponent (Figure 4.13).

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If the service life of a zero-maintenance façade system is doubled, say from 30 to 60
years, the embodied impacts are essentially halved. Then a major replacement or
renovation returns the service quality to original (or enhanced) performance
specifications and resets the service life clock, accompanied by a new debt of embodied
impacts. However, if maintenance and renovation activities are required to extend the
service life of the system as suggested here, these must be accounted for. Maintenance is
not free. Maintenance and renovation cycles produce recurring embodied energy, which
adds to the lifecycle embodied energy debt and offsets embodied energy gains resulting
from increased service life (Figure 4.13). These maintenance and renovation activities
will also likely improve energy efficiency during the following operational cycle of the
building or system. The complexity is in determining the net benefit (or cost), including
environmental and operational energy impacts, resulting from a renewal strategy—does a
longer service life achieved through planned maintenance and partial renovation cycles
reduce embodied impacts and improve lifecycle energy as compared to a replacement
strategy with the entire façade system demolished and replaced in repeated temporal
cycles? Analysis is required to determine lifecycle embodied impacts and operational
energy performance, and comparative scenarios modeled with varying initial embodied
energy debt, recurring embodied energy inputs, energy consumption from building
operations, and service life. Complementary lifecycle tools and processes can be used in
combination in this pursuit: lifecycle costing analysis (LCCA), maintenance planning,
Service Life Planning (SLP) and lifecycle assessment (LCA), in assembling a
methodology for evaluating such strategies.

Figure 4.14: Cyclical renewals may extend service life by periodically elevating service quality
(adapted from Iselin and Lemur 1993, 22; Kesik 2002).

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4.4.9 More embodied impacts and durability considerations
The primary focus of the preceding analysis has been technical design solutions to largely
technical problems of material degradation, durability and service life. Section 4.3.6
points out that the current reasons for building demolition and major façade renovations
are not a result of weathering processes, but rather obsolescence factors including the
rather arbitrary considerations of fashion and style. The overwhelming predominance of
first-cost considerations in a near complete absence of lifecycle thinking also colors
various aspects of design and management processes in ways that magnify embodied
impacts. Considerations must be constantly balanced with those of embodied carbon to
assure the lowest possible carbon footprint.
Attributes of low carbon assemblies:
Sustainable design practice should encompass the consideration of low carbon assemblies
(LaRoche 2017; Cheung and Faretani 2016). See Table 5.6 for primary attributes of low
carbon assemblies with particular reference to the design and delivery of metal framed
curtainwall systems.

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Supply chain aberrations
The importance of lifecycle thinking is not reflected in current façade design and delivery
practices. Supply chain logistics are a prime example. Every façade contractor has similar
stories: glass made in China is shipped to the U.S. for coating, then returned to China for
assembly into curtainwall units, which are then shipped back to the west coast of the U.S.
and trucked across the country for installation on a tall building under construction in
Manhattan. There is no possibility for this to make sense from the standpoint of lifecycle
embodied GWP. The false accounting practices common today of first-cost and pay-
back-period ignore lifecycle impacts entirely, and cheaper offshore labor costs can
provide monetary savings.
Figure 4.15 diagrams a typical supply chain for a curtainwall project. Materials and
components converge on the assembly facility as well as the jobsite. This project
benefited from an assembly facility set up within 60 miles of the jobsite to facilitate
delivery of this project.
Table 4.6: Attributes of low carbon assemblies.
Access and ease of
assembly/disassembly
for purposes of:
(Cheung and Faretani 2016, 40)
inspection, repair, maintenance, retrofit, renovation
reuse and recycling
other forms of adaptation
disposal
Material selection considerations
(Reddy 2009, 171)
energy intensity of materials
quantity of raw materials and natural resources consumed
reuse and recycling potential, and safe disposal practices
maximize recycled content in materials and finishes. This is especially
important with aluminum, where recycled content can vary as much as
80-90 percent between suppliers (Cheung and Faretani 2016, 40)
environmental impacts
Purchasing strategy
and supply chain management
(Shaw et al. 2012; Ramudhin et al. 2008
low transportation costs, especially for heavy materials like glass and
steel, drives consideration of local sources (In the case of glass, this
may not be possible.)
strategically locate and coordinate between vendors to minimize
transport cost
utilize principles of circular economy (Ellen MacArthur Foundation
2017)

185

Figure 4.15: Procurement of curtainwall materials and assemblies for the LA Live Tower ( 2010, Los
Angeles, Gensler, façade contractor Enclos).
Lifecycle thinking highlights the value of purchasing from a leading manufacturer of
quality architectural products. Architectural glass products are an example. There are
many choices in product makeup and supply. Purchasing exotic products in
unconventional shapes and sizes from distant offshore suppliers increases the possibility
of future difficulty in procuring replacement products to match existing façade glass.
Obsolescence and the curtainwall system
Obsolescence is an important consideration in the determination of an appropriate design
service life for a curtainwall façade system—and a mandatory input for lifecycle
assessment. The modes of obsolescence identified in section 4.3.6 are intended to help
balance social, economic and environmental considerations in the pursuit of an optimized
outcome. Every façade system—and every façade system component—should be
evaluated during the design phase in the context of obsolescence. This could be
accomplished in the form of an audit that addressed the following issues (derived from
Burns [2010, 50-51]), using the Owner’s Project Requirements (OPR) and the architect’s
Basis of Design (BOD) as initial source documents.
§ the building type and use for which it is intended
§ the design service life of the building

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§ climate and site conditions
§ resilience assessment and repairability analysis
§ a system specific repair, maintenance and retrofit/renovation plan
§ lifecycle cost analysis (LCCA) and budgeting
§ the availability of products and supporting trades (fabrication and installation)
§ end-of-use plan for reuse, recycling or disposal
§ a lifecycle assessment to determine environmental impact
§ reliability assessment and failure consequences
§ potential for technological change and consideration of system-ready adoption of
anticipated new products/technologies
§ potential for changes to codes and standards
§ heritage potential of building and façade system
§ durability and differential durability assessment of all novel materials, products,
finishes, and design details included in the system design
The primary strategy to minimize the service life threat presented by factors of
obsolescence is to maximize the adaptability of the façade system to the greatest extent
possible.
Material and design complexity: The shape of things to come
The two dominant trends in commercial architecture today are escalating geometric
complexity of building form and an expanding palette of materials used in the building
skin, both of which challenge service life estimations (Patterson 2015). These trends
reduce the effectiveness of past experience, documentation and testing as applied to
service life forecasting. Increased complexity impacts the entire building process,
bringing heightened durability challenges to design detailing, material specification,
fabrication, installation, operations, maintenance, and disposal, that threaten building and
building system service life. Complexity brings compromise to resilience and
redundancy, a direct threat to service life, thereby making complexity a sustainability
consideration.
The current pursuit of extravagant geometric form in buildings makes them less adaptable
and more difficult to repair and maintain. Brand (1994, 192) promotes the rectangle as
the most efficient spatial configuration in terms of adaptability and use. This is equally

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true of the façade system. Brand notes that, “…convoluted surfaces are expensive to
build, a nuisance to maintain, and hard to change.” Enabled by design tools that facilitate
the development of complex forms, architects are busy designing “green” buildings that
defy modularity and challenge rationalization, requiring specialists to interpret the
surfaces for fabrication and installation. These buildings will be difficult to adapt to
changing conditions of use in the effort to avoid obsolescence, creating a heavy future
debt, either in the form of costly renovations, reconstructions and replacement, or in
subjecting users to substandard quality and the accompanying social and environmental
impacts. A real commitment to sustainable buildings will see a return to orthogonal grids
in plan and elevation.
Innovation is a double-edged sword. Stepping toward a sustainable built environment
demands innovation at every level across the building process. Innovative solutions are
needed and hopefully forthcoming in response to the durability challenges. Yet
innovative solutions developed in response to myriad other building challenges often
ignore impacts to durability, maintenance and embodied energy. Double-skin facades are
an example. Such systems are often developed in parallel with energy modeling that
reveals their impact on energy performance, but without accompanying service life
analyses and planning and lifecycle assessment, the result may not represent a sustainable
outcome.
Industry practices to reduce embodied impacts
Richards (2015, 159) touches on many of the above points in suggesting the following
activities as likely developments in coming years as the building industry attempts to
mitigate embodied carbon impacts:
§ Alternative framing materials with lower energy intensity, such as low-
temperature plastics and timber.
§ Reduced embodied carbon impacts from material production with high energy
intensity materials like aluminum and glass.
§ Increase in glass recycling.
§ Advances in precast systems in façade applications.
§ Reuse of aluminum profiles. This will require a higher level of system
standardization, and a practice of designing for reuse.

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§ Extended service life of insulated glazing products through improved cavity
closure systems.
4.4.10 Lifecycle and the value of durability
Lifespan is the appropriate but seldom utilized measure of building cost. There are three
generic approaches to buying out building systems, products and materials.
1. First-cost purchasing strategies—commonplace among private commercial
property developers—consider only the initial cost of the building, building
system, or material. No consideration, for example, is given energy savings that
might result from building operations; buying decisions are made based on lowest
cost from the pool of products that meet building code minimum requirements.
2. A payback strategy considers such operational savings, but over a limited
specified time, often 1-3 years but occasionally as long as 10-years. Using a
window as an example, if the energy savings resulting from the use of a higher
performing product offsets the additional cost in a given payback period, the
higher performing product will be considered. Short-term payback strategies are
sometimes adopted by private commercial property developers, but are more
typical of owner-occupiers, such as corporate headquarters or institutional
buildings, especially with the longer payback options.
3. Finally, is the far less common lifecycle costing analysis (LCCA), where costs are
analyzed based on integrated building performance over the full lifecycle of a
building. This is often in conjunction with other lifecycle tools like LCA,
maintenance and service life planning.
A building developer specializing in leaseholds as an investment strategy has little
incentive to invest additional sums in green building options, unless they can be
convinced that the investment will increase lease and occupancy rates in a manner that
will quickly (1-3 years, typical) pay off the additional investment. Their payback
horizons from an investment standpoint are very near. Energy costs, for example, are
generally paid by the lease holder, effectively stripping the developer of any motivation
to invest in products or systems that would improve energy efficiency; the so-called split
incentive (Olgyay and Seruto 2010; Frey 2011, 85-6). The building, however, may have a
lifespan easily measured in decades. Very few of the early twentieth century tall
curtainwall buildings have been demolished. Decisions made based on first-cost or short-
term payback burden building performance, the built environment, and ultimately,
society for many decades.

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Examining and changing policies might be one solution incentivize building envelope
practices. The green building movement has had some success in convincing developers
that positioning their buildings as green assets would result in improved lease and
occupancy rates, and therefore profits, and at least some developers have voluntarily
embraced this strategy report successful outcomes. However, getting the uptake required
to speed the transition to a carbon-neutral building sector will likely require increased
regulation and legislated action in the form of far tougher building codes.
4.4.11 Radical innovation
Sustainability may be a design problem, but solutions to the problem of durability in
buildings, and sustainability of the building sector, will require widespread innovation in
design as well as in other areas of practice. Thomsen (2017, 6) cites the invention of the
float glass process by Sir Alistair Pilkington in 1952 as the last breakthrough innovation
in the glass industry, claiming the industry is “mired in incrementalism,” and claims
industries without step change every 30 years or so are at risk of failure. The façade
industry, with glass at its core, is ripe for radical change.
Façade system leasing: An innovative delivery strategy with disruptive
potential
Delivery strategy could be a disruptive innovation. Façade systems are typically bought
by the owner, or by the owner through a general contractor, from a specialty façade
contractor. The façade contractor designs, supplies and installs an engineered façade
system in accordance with the project contract documents. Once the work is accepted as
complete, the façade contractor is done. The operation and maintenance of the system
falls to the owner’s facilities management team, a separate silo in the building industry.
As façade systems have become more complex, involving increased automation and
integration with other building systems, problems have emerged with maintenance and
operations of these systems.
Disruptive innovations are not only the purview of design development. There was
nothing new in the concept of a hired automobile ride, taxi services have been operating
for decades, but Uber had a different concept for delivering these services to the
marketplace. The possibility for such innovation exists with curtainwall design and
delivery, where the same processes have been in place since the advent of the technology
in the mid-twentieth century. Nicol (2016) suggests the possibility of owners leasing

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glass from industry providers, which raises the interesting prospect of façade system
providers leasing entire façade systems directly to building owners, including design,
fabrication, installation, services as well as ongoing maintenance, repair, retrofitting and
renovation services. The façade supplier—perhaps not the same façade contractors that
supply metal curtainwall systems today; Nicol suggests the glass industry step into this
role and sell a specified level of performance for a defined period, including
maintenance, repairs, and code mandated retrofits over that time period. The cost to the
building owner would be amortized over the lease period, minimizing first-cost. The
benefit would conceivably be in the expertise in implementing and maintaining façade
system performance over extended durations, rather than leaving the important aspects of
maintaining performance to the varying capabilities of building ownership. A building
owner planning on turning over a building within 5-10 years may have little interested in
the durability and performance of the façade system, but the façade system owner would
have a vested interest over the full lifecycle of the building; the longer the better.
4.5 Guidelines to enhance façade system sustainability through
considerations of durability and embodied carbon
The following generalized design guidelines for curtain wall systems in new building
applications can improve the durability, adaptability, and implementation of future
curtain wall retrofits, potentially reducing building life-cycle cost.
Design for durability: Façade design is strongly linked with sustainability through a
pathway of durability. The lessons of durability reveal best practices are often counter-
intuitive. Building and façade designs that fail to account for durability are unlikely to
realize sustainable outcomes.
Physical wear and deterioration, particularly to materials, finishes and components
exposed to the elements, as with façade systems, commences on day one and progresses
with time. But degradation is only part of the problem, and perhaps the easiest part to
manage. Change, in its many forms, is inevitable, and carries the constant threat of
obsolescence. Planning and action is required to circumvent the impacts of these
phenomenon on the service life of a façade system. The following assumes the goal of
long building service life. Buildings designed for service life of 60 years or less, should

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consider shifting focus to disassembly and end-of-life disposition of materials, preferably
through reuse, with all else up-cycled or recycled.
The following strategies can be employed to
§ recognize and correct patterns of physical deterioration
§ anticipate and avoid obsolescence, thereby extending service life indefinitely.
§ minimize carbon intensity of materials and assemblies
The strategies employ integrated concepts of material selection, maintenance and
adaptability involving design, analysis, and planning processes with the objectives of
§ embedding adaptive capacity within the design of the façade system, and
§ designing maintainable systems that both minimize the need for and optimize the
ease of maintenance,
§ providing low carbon curtainwall assemblies,
§ adopting minimalist low carbon impact strategies for repair and maintenance, as
well as future retrofits and renovations
Pre-design and early design strategy
Documentation of project performance requirements and design intent takes place in this
important phase. Program goals are developed and formalized in two important guiding
documents (WBDG 2016):
1. Owner’s project requirements (OPR): developed in pre-design and documents
the owner’s directives for the building program, including building scope,
schedule, budget, and other relevant criteria.
2. Basis of design (BOD): developed in response to the OPR by the
architect/engineer very early in the design process, focusing on technical
approach and design features.
Both of these guiding documents should address the façade system in detail, especially
the BOD. Key performance parameters of thermal, solar, and acoustical performance
should be articulated, along with service life definition, and other sustainability and
resilience metrics. Requirements for repair, maintenance, retrofit and renovation planning
should be defined in the BOD. (Sample documents of the OPR and BOD are available
online from various sources, including ASHRAE, the Building Commissioning
Association, the US Department of Energy and other sources.)

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Plan for an integrated whole-building design, analysis and planning process commencing
early in design development, incorporating the façade system as a key consideration, and
involving lifecycle assessment (LCA), lifecycle costing analysis (LCCA), and service life
planning (SLP). SLP will include specific durability and maintenance planning, and
require the definition of design service life. Design development will progress in an
environment of constant feedback on design decisions from ongoing processes of LCA
and LCCA, the former providing information about material selection and embodied
impacts, with the latter revealing costing implications. SLP will provide ongoing inputs
to LCA, LCCA and other processes regarding maintenance requirements and durability
parameters. Maintenance and adaptability considerations will be embedded in the system
design.
The participation of a commissioning agent is also required early in the initial planning or
early design process, and the development of a commissioning plan that specifically
addresses the façade system, and includes a post-occupancy program to assure initial
performance, and ongoing commissioning to assure proper operation and maintenance
procedures into the future.
Façade system planning
Note that existing standards and guidelines do not adequately address glass and
aluminum curtainwall systems with specificity, so appropriate planning documents will
need to be developed by the planning and design team.
1. Service life: Define a curtainwall service life in harmony with building service
life.
2. Fit and function: Review design guidelines and criteria to assure fitness to
building type. This should be done frequently for building types subject to rapid
technology development: hospitals, laboratories, data centers, schools,
correctional facilities, and others.
3. Obsolescence: Perform an obsolescence assessment (see 39-46 below).
4. Durability planning: Develop a durability plan per the latest relevant versions of
ISO 15686 or CSA S478-95. Include all phases from design development through
end-of-life disposal. Include all materials, finishes and components.
5. Façade commissioning: Develop a façade commissioning plan per LEED v4 or
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installation work. Include provision for post-occupancy data collection, analysis,
and corrective action.
6. Maintenance planning: Develop a maintenance plan; per relevant GSA
documents, including Architectural and Interior Design (GSA 2005), the National
Operations & Maintenance Specification (GSA 2012), and other relevant codes,
standards and guidelines; that anticipates cycles of maintenance, retrofit, and
partial renovations for the curtainwall system as required to perpetuate service
life. Include provision for periodic review, assessment and updating of plan. This
is a living document that should evolve over the lifespan of the building. This is a
core document intended to support a renewal strategy that perpetuates building
service life indefinitely.
7. Material selection: Conduct an LCA of the façade system to optimize material
use per the most recent version of ISO 14040. Include comprehensive supply
chain
8. Lifecycle costing assessment: Conduct an LCCA of the façade system to
optimize lifetime economic performance per the most recent version of ISO
14040.
9. Design service life: Establish a design service life baseline that harmonizes with
the building design service life. Consider adopting a perpetual service life
strategy.
Façade system design parameters
General principles
10. Differential durability: realize the service life potential for each component of
the façade system, with the goal of no wasted durability.
11. Adaptability: establish flexibility and adaptability as explicit design goals in
OPR and BOD. Consider such strategies as:
• unconstrained interior space in the façade zone
• uniform orthogonal modularity
• uniform orthogonal glazing grid
12. Circular economy: reuse or recycling (not down-cycling) of all materials and
assemblies.
13. Design loads: Design using predicted weather data (not historic) from global
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14. Recurring impacts: design to both minimize and facilitate repair, maintenance,
retrofit and renovation to minimize recurring embodied carbon.
15. Integrated design process: design to accommodate service life planning,
durability plan and maintenance plan, and to support optimal repairability,
maintainability and adaptability.
Design parameters
16. Design detailing: detailing should anticipate future retrofit of new technologies,
and future expansion of the building envelope.
17. Reuse: Incorporate used materials and assemblies where ever possible.
18. Recycled content: Incorporate as much recycled content as possible in all
materials, especially carbon intensive materials like aluminum
19. Disassembly: Design for ease of assembly and disassembly to support repair,
maintenance, retrofitting, and other processes of adaptation.
20. Mockups: Use full scale façade zone mockups as required to determine
functionality in response to user’s needs.
21. Glass retrofit and repair: Glazing materials should be easily changed out from
within the building during off hours.
22. Spandrel retrofit and repair: Spandrel assemblies should be accessible,
removable and replaceable from inside the building during off hours, or from a
conventional window-washing rig.
23. Glazing and panel cassettes: Consider a cassette strategy for all panel materials
to facilitate the easy installation and removal of the glazing panel.
24. Seal access: All gaskets, air and water seals should be inspectable, removable,
reparable and replaceable, designed to facilitate defined inspection, repair, retrofit
and maintenance procedures.
25. Bonded assemblies: Avoid bonded assemblies if at all possible. They lack
adaptive capacity and lock in differential durability issues that lead to wasted
durability. Bonded assemblies are the antithesis of a perpetual renewal strategy.
Utilize dry compression gasket strategies that can be removed from the façade,
disassembled, repaired, reassembled, and reinstalled as a planned maintenance or
retrofit procedure.
26. Reduce exposure: Isolate materials and finishes exposed to the elements and
design them for extended durability.

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27. Repair, maintenance and retrofit: All materials exposed to the elements should
be easily removable and replaceable, preferably from inside the building, but if
not, then from a conventional window-washing rig.
28. Operability: Identify operable systems and components in the curtainwall and
assess durability based on projected usage. Mandatory design for ease of
maintenance and retrofit.
29. Interlocking unit frames: Avoid interlocking curtainwall frames between units;
any single unit should be removable without the removal of or damage to adjacent
units.
30. Finishes: minimize exterior exposure of system components and finishes to
greatest extent possible, isolate them and facilitate access, repair and renewal.
31. Anchorages: design to match the service life of the structural system; design on
the basis of predictive, not historic, weather data; should be accessible for
inspection, repair and replacement if required.
32. Replacement of exterior components: Develop a strategy for easily replacing
exterior opaque assemblies from inside the building or from a conventional
window-washing rig. Consider designing exterior finish panels as removable from
insulated assemblies so they can be changed without removing the entire panel
assembly.
33. End-of-life: Develop an explicit plan for end-of-life options. Design for system
deconstruction and reuse, articulating a strategy of zero-waste in the case of
system decommissioning.
34. Durability and carbon: Balance durability and embodied carbon considerations
in a lifecycle context, e.g., higher carbon materials may last longer, producing a
net lifecycle reduction, especially finishes.
Other considerations
35. Frame material: Consider alternate framing options with reduced embodied
carbon and lower thermal conductance.
36. Evaluate WWR: Limit window-to-wall ratio (WWR) to that needed for daylight,
view, connection to nature, and natural ventilation.
37. Spandrel areas: In non-vision areas, use spandrel materials with lower embodied
carbon and high insulation values, or power generation capability.
38. Systems integration: While not a durability consideration, façade systems should
be fully integrated and automated with other building systems, including: shading
and glare control, lighting, HVAC and mechanical systems.

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Anticipating obsolescence
39. Obsolescence report: Perform an obsolescence assessment and compile a report
that includes the following items (40-46):
40. Fit and fitness review: Periodically review facilities programming to anticipate
future functional requirements for the building skin.
41. Trend analysis (ongoing): cyclical assessment of trend development in
local/regional area regarding: urban development, office use, telecommuting,
apartment and condominium lifestyles, building codes, community resilience and
sustainability programs, land use, neighboring urban development, transportation
network, and other criteria recognized to influence building use.
42. Style assessment: Review stylistic trends in architecture and their façade systems
in the neighborhood of the building site.
43. New technology: Research new and emerging material, product and technology
developments; e.g., the latest advances in architectural glazings, insulation
products, and finishes.
44. Workplace utilization: Review evolving patterns of user facility requirements
for the building type.
45. Systems integration: Review anticipated trends in building systems integration
and how they might interact with the façade system.
46. Anticipate obsolescence: even if designing to prevent it. Design to accommodate
retrofit, disassembly and reuse.
Material procurement & fabrication
47. Sourcing: Purchase products and finishes available from multiple local sources.
For function-critical items like vision glass, assure that sources are common
enough as to be available for future procurement.
48. Recycled content: Maximize verified recycled content. Require an environmental
product declaration (EPD) or similar verification.
49. Supply chain analysis: Analyze supply chain to assess embodied carbon of all
materials and assemblies, especially high intensity materials like aluminum and
glass. Give special attention to transport and fuel source (e.g., coal versus hydro).
50. Service life planning: Assure fulfillment of CSLP by providing quality repair,
maintenance, retrofit and renovation of façade system per the plan throughout
operational cycle of the building.
51. End-of-life: When the decision is made to terminate the building or façade system
service life, define and implement a strategy that prioritizes reuse above

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recycling, and recycling over disposal. The goal should be zero-waste in support
of the circular economy.
4.6 Summary, conclusions, and discussion
This section summarizes findings and discusses the implications of this chapter.
The building façade is central to the pursuit of sustainability in buildings and the built
environment. Hartkopf and Loftness (1999, 382) stipulate four parameters of what they
term total building performance: 1) user satisfaction, 2) organizational flexibility, 3)
technological adaptability, and 4) environmental and energy effectiveness. The building
façade clearly impacts each of these areas in a profound manner. In addition, the façade
provides much of the character and visual appearance of buildings and urban habitat,
uniquely impacting considerations of both appearance and performance like little else in
the built environment. The building skin may provide the key to sustainable buildings and
urban habitat through an integrative balancing of the various attributes of sustainability
that converge at the facade. Primary among these attributes are durability and energy,
more specifically embodied energy, as it relates to considerations of durability and
service life. Much research has and is focused on operational energy efficiency. The
embodied impacts of building consumption falling outside the operational cycle have
relatively recently come to the forefront as a research pursuit. Little of this has focused on
the building façade system. This chapter has focused on a façade system of a specific
type—the metal-framed or glass and aluminum curtainwall system—a dominant system
type in large commercial and high-rise residential building applications.
Conclusions
The following summarizes the findings and conclusions for metal-framed curtainwall
systems:
1. Durability is a critical consideration of sustainability.
Durability, differential durability, wasted durability, the various forms of service life;
design, predicted, potential and the related considerations of embodied impacts, both
initial and recurring, are critically important sustainability considerations. Section 4.3

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2. Curtainwall systems are high embodied-impact assemblies.
Aluminum and glass represent 93% of conventional curtainwall material makeup, both
high embodied energy materials. Section 4.4
3. Curtainwall renovations amplify the embodied impact of the façade system.
Curtainwall system replacement, as the leading form of façade renovation, more than
doubles the embodied GWP of the façade system, carries a burdensome cost impact, and
introduces a social impact in the form of disruption to ongoing building operations during
the construction process. Sections 4.2, 4.4, 5.2
4. Extended service life is an effective countermeasure to embodied impacts.
Extending service life of the façade system is an effective strategy for reducing lifecycle
embodied impacts. Section 4.3.3
5. Obsolescence and not degradation is the leading cause of service life
termination.
The reasons for service life termination of the façade system are poorly understood, with
degradation assumed as the primary, quantitative and technical causal force. The reality is
more complex, qualitative and highly subjective as represented by the various forms of
obsolescence that limit service life. Section 4.3.6
6. Adaptability offsets the threat of obsolescence.
Façade systems that are designed for easy adoption of new and higher performing
products, adaptation to changing conditions of use and style, and other manifestations of
change, can best resist the forces of obsolescence that limit service life. Section 4.3.7
7. Upgradability is a form of adaptability.
Façade systems for TCB applications must be upgradable, both technically and
stylistically. 4.3.7

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8. Zero-maintenance curtainwall systems is a mythology of convenience.
The representation of curtainwall assemblies as zero-maintenance systems is a
misrepresentation. It would be more accurate to say they are not maintainable. They last
through a relatively short service life, typically with low maintenance requirements, but
their design supports little opportunity for system renewal through maintenance, retrofit
and renovation short of complete system replacement. Section 4.4.8
9. Service life planning (SLP) can extend service life.
SLP specifically addressing the façade system, including durability and maintenance
planning and involving repair, maintenance, retrofit and renovation procedures and
schedules, is an effective strategy to extend façade system service life that reduces both
embodied and operational impacts. Sections 4.3.9, 4.3.12
10. Recurring embodied impacts must be considered.
Repair, maintenance, retrofit and renovation occurring over the service life of the façade
system add to the total embodied GWP debt, in the form of recurring embodied GWP.
Curtainwall systems must be designed to both minimize and facilitate the ease of
recurring maintenance, retrofit and renovation requirements. Sections 4.3.3, 4.3.9, 4.4.8
11. Service life benchmarks are inadequate.
New benchmarks for building and façade system service life are needed—current service
life guidelines do not represent sustainable outcomes. Section 4.3.11
12. Buildings and façade systems must embrace zero-waste processes.
Building and façade system design and delivery practices do not embrace closed-loop
processes and support the circular economy, burdening the solid waste stream. Most have
no plan for end-of-life processing. Section 4.3.6
13. Demolition and replacement as a last resort.
Building and façade system demolition and replacement should be an act of last resort.
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maintenance, retrofit and renovation requirements, and the need for adaptive capacity to
counter obsolescence forces. Section 4.2.1
14. Façade replacement as the dominant renovation strategy.
The failure to anticipate as stated in “demolition” above, results in replacement as the
dominant façade renovation strategy, with consequences of wasted durability, amplified
embodied impacts (environmental), as well as economic, and social impacts, thereby
compromising all three “pillars of sustainability.” Section 4.4.7
15. Curtainwall as the weak link in building durability.
The cost, disruption, and risk to the owner of complete façade replacement forces
consideration of building replacement. Section 4.4.7
16. Curtainwall systems waste durability by design.
Differential durability issues in contemporary curtainwall design collapse the service life
of durable, high embodied energy materials to that of the weakest link: the gaskets and
seals of the IGU and/or curtainwall units, resulting in significant compromise to service
life potential and wasted durability, amplifying embodied impacts. Section 4.4
17. Time value of carbon considerations.
There is an important temporal consideration to minimizing embodied GWP, maximizing
the potential value of short term reductions. The continued use of aging façade systems,
perhaps with the benefit of low embodied impact retrofits and renovations, may be a
superior strategy to their replacement with a high-performance system if decades of
energy savings are required to offset the initial embodied impacts of the new system.
Section 4.2.1
18. Bonded assemblies do not support sustainability goals.
Bonded assemblies like IGUs and wet-glazed curtainwall units, typically bonded with
silicone adhesives, sacrifice service life duration by failing to facilitate inspection, repair,
maintenance and retrofit of curtainwall systems. Section 4.5.6

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19. Paradigm shift in durability thinking needed.
Durability in façade systems is seldom considered, and inadequately so when it is.
Embracing the concept of the circular economy demands a new way of thinking about
durability as an ongoing process of renewal, and service life as perpetual; indefinite
service life terminated only on demand with the activation of an end-of-life material
disposition and distribution plan. Section 4.4.11
20. Building tomorrow’s problems today.
Like the early mid-twentieth century curtainwall assemblies, contemporary systems
completely fail to anticipate a need for future repair, maintenance, retrofit or renovation,
the very problem that has let to system replacement as the dominant renovation strategy
for aging façade systems. They lack adaptive capacity, and are highly vulnerable to the
escalating effects of climate change, as well as the forces of obsolescence resulting from
accelerating social change.
21. Contemporary curtainwall system design and deliver practices do not
support sustainability goals for buildings and urban habitat.
Remedies to these problems are neither simple nor obvious, but they are achievable, with
the absence of will to effect such change as the major substantive barrier. Guidelines for
new curtainwall system designs introduce constraints that will drive radical change in
curtainwall technology (Section 4.5: Façade system design parameters).
Discussion
Contemporary aluminum and glass curtainwall systems present a significant challenge to
the realization of sustainable built environment. The emergence and persistence of the
highly-glazed building façade was accompanied by high air (and sometimes water)
infiltration through leaky framing systems, poor thermal and acoustical performance,
problematic solar behavior, interior and exterior glare, condensation issues, and other
problems resulting in generally high rates of building energy consumption combined with
poor conditions for occupant comfort. Yet the systems remain popular with building
occupants, and therefore with developers, and demand for these systems remains high.
Much has been done to improve curtainwall system performance, primarily by the glass
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combining laminating and insulating process with an ever-increasing array of solar and
low-emissivity coatings that improve solar behavior and insulation values. In the process,
however, little consideration was given to the durability of these assemblies, to the
wasted durability produced by differential durability characteristics within the
assemblies. The result is an unacceptable collapse of the service life of highly durable
float glass and mill-finish aluminum, and amplified embodied GWP as the assemblies are
replaced. The singular goal must be to realize the full potential service life of every
component of an assembly.
Glass and aluminum, the dominant curtainwall components, are both high embodied
carbon materials. They each provide significant attributes in curtainwall systems, but
their continued use as dominate façade materials must be accompanied by a substantial
increase in their service lives, in a durability scenario that maximizes the service life of
each component. The same is true of the building itself. The commitment of material
resources represented by tall curtainwall buildings essentially mandates a higher priority
shift to the optimization of whole-building service life. The structural system is a good
place to start in determining building service life, and harmonizing the façade system
service life with the building. Realizing the durability potential of the structural system
suggests an approximate 300-year service life, well beyond current standards and
perceptions of appropriate building service life. These buildings could be designed to last
at least this long, and a prerequisite to construction should require a durability and service
life plan that documents the intended repair, maintenance, retrofit and renovation
procedures and schedule over the building lifecycle, complete with an LCA disclosing
predicted lifecycle GWP from embodied and operational sources.
It is entirely possible, if not likely, that seriously addressing these considerations will
drive new façade system strategies away from the currently dominant metal-framed
curtainwall systems. A possible direction is suggested by the simple concept of a largely
opaque and heavily insulated unitized mega-panel with conventional punched windows,
using existing prefabricated window products. Existing high-performance window
products are currently available as unbonded assemblies, meeting passive house
standards, that are far more amenable to repair, maintenance, retrofit, renovation, and
even replacement procedures than conventional unitized curtainwall systems. Mega-
panels would minimize joints between units. The challenge is in designing a sealing
technique between the units that meets the design criteria in section 4.5.

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A 300-year design service life may ultimately not be enough to validate the sustainability
of this building type, but it is a worthy improvement over practices to date. It also
establishes a new context for the façade and other major building systems, manifesting
new constraints that could drive breakthrough developments in urban planning, and the
design of buildings and their curtainwall systems.
Beyond, and in addition to, a roughly order-of-magnitude extension of service life,
fundamental building program lifecycle goals should:
§ Embody enough adaptive capacity to meet the evolving functional needs of the
users.
§ Maintain uninterrupted minimum specified service quality in both the inside and
outside contexts.
§ Achieve carbon neutrality over the building service life.
This last is perhaps the most challenging. Carbon neutrality goes beyond zero-energy
standards by accounting for embodied impacts, largely owing to material considerations.
Highly efficient low-energy buildings tend to achieve their efficiency through amplified
embodied GWP debt, a problem, especially in the context of the time value of carbon.
Carbon accounting reveals this false economy. The relatively few but growing number of
data-verified zero-energy buildings are primarily comprised of smaller single-story or
low-rise buildings 4 stories or under, relying heavily on roof-mounted PV. The geometry
of tall buildings eliminates this strategy. Autonomous energy supply in tall buildings
requires activation of the façade system. Effective building-integrated photovoltaic
(BIPV) technology remains a decades-long unrealized promise, but developments
continue; a good reason to anticipate the need for future façade retrofit in new building
under design, and provide curtainwall systems that can easily accommodate the retrofit of
higher performing components.
If these emerging developments are solar driven, then solar access and the work of
Knowles (2003) is finally brought to the forefront and integrated into urban planning,
which would suggest a possible end to the dense clustering of tall buildings as
exemplified by Manhattan. Ernest Flagg, the architect for the once-tallest now
demolished Singer Building constructed in New York City in 1906, was an early critic of
the skyscraper for just this reason (O’Connor 2016). The sustainability of the tall building
type is occasionally and justifiably called into question (Roaf 2009; Massey 2013; Sturgis

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2016). Sustainability is a somewhat relativistic, and certainly contextual consideration.
Scale is one aspect of context. A celestial space exploration program not sustainable at
the city or state level may become so at a national or international scale. The same is true
of tall buildings; there may be a place for the building type in sustainable urban habitat,
but the context may be significantly different than that of today. The relativism is in the
prevailing societal perception of value; societies will make considerable efforts to sustain
that which is value, potentially even shifting finite resources in painful ways. A barrier to
change today is that the pain is not equally distributed, with key influencers and decision-
makers essentially insulated. Climate change will likely level this playing field, perhaps
quite literally.
In any case, there is an evident cross-cultural penchant for the tall highly-glazed
curtainwall building form among both building developers and users, and similarly, a
long-running trend of increasing heights. It is clear that at least in the short to mid-term
this will continue, and should, at minimum, be coupled with a deeper consideration of
embodied impacts and durability considerations, including mandatory requirements for
extended service life. It is equally clear this is unlikely to happen, and so tall curtainwall
buildings will continue to burden the built environment with embedded impacts
compromising future sustainability.
There are other good reasons to reorder expectations regarding service life, as
exemplified by the current dilemma of the aging stock of existing mid-century
curtainwall buildings. Even in these robust economic times and the boom in new building
construction, especially in areas like New York City, needed curtainwall renovations are
being postponed for economic reasons. New tall building construction poses a similar
future threat, with the new curtainwall systems possessing a service life no longer, and
possible shorter, than their progenitors. The unprecedented uncertainties of global climate
change possess an economic component, rendering future economic conditions equally
uncertain. Population increase and escalating material resource depletion will add to this
economic strain. Damage to the building stock resulting from amplified storm magnitude
and frequency could result in a significant reduction in serviceability and service quality.
Even in the absence of such shocks, the gradually accumulating stresses of obsolescence
from, for example, accelerating social change may render buildings and their façade
systems unserviceable. It cannot be assumed that the economic wherewithal to deal with
such eventualities will be available in this uncertain future.

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The opportunity is to embed options rather than burdens in buildings and their façade
systems. The challenge in accomplishing this, outside of adoption, is providing these
options while mitigating the recurring and, especially, the initial embodied GWP. This is
evident in the m-IGU described in Chapter 5; design solutions can be envisioned, but it is
nearly impossible to realize them without some additional material and labor, and
certainly some recurring maintenance cost, which will add to the lifecycle embodied
GWP. This is similar to the pattern of high-performance buildings carrying a higher
embodied GWP profile. This will only work in a lifecycle context, and with significant
extension of service life over contemporary measures. In any case, the time value of
carbon suggests an emphasis on reusing, or continuing the use, of what is already there.
Unfortunately, curtainwall design and delivery practices have left a challenging legacy in
this regard.
Considerations of embodied GWP and the time value of carbon make it clear that
building demolition and replacement should be a strategy of last resort. The same is true
of the metal and glass curtainwall façade system. Unfortunately, the options are few, and
in the absence of appropriate lifecycle metrics, façade replacement is most often the
selected option, in itself an indictment of past curtainwall design practices. Options for
the façade renovation of existing curtainwall buildings are discussed in Chapter 7. The
fundamental problems with curtainwall technology in its past and present forms have
been the subject of this chapter, and an effort made to illuminate the path forward toward
a future where the façade system plays an integrative role in achieving optimized
building lifecycle performance and a sustainable built environment. This achievement
will require a different way of thinking about façade system durability and the
appropriate service life for buildings.
Designing for the ages: A strategy of ongoing renewal to perpetuate service
life
Not that long ago, building designers designed for “eternity” (Henket 1996, 13). While
certainly not appropriate for all buildings, the concept of perpetual service life becomes
relevant at the scale of the TCB. It is conceivable to again reset the bar by extending the
service life of the building structural system beyond the 300-year mark. If the building
enclosure is properly maintained and provides adequate protection from the elements, the
design and construction of structural systems capable of service life well beyond 300
years is achievable. One can even envision structural systems designed to accommodate

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the replacement of structural components, if needed, without interruption to building
service. The same concept can apply to each material and component that makes up a
building, including the metal and glass curtainwall system. The notion is one of ongoing
renewal perpetuating service life indefinitely until a decision is made to terminate,
disassemble the building and redistribute the materials into the closed loop of a circular
economy. It is conceivable that at the end of a building’s service life not a single original
component remains, but the building has been in continuous service throughout its
lifespan. The notion seems far-fetched based on common perception of longevity, but it is
simply one of design and delivery practice bounded within a defined set of constraints
and grounded in fundamentals of durability science.
Net lifecycle performance gains are conceptually possible through the adoption of
maintenance and renovation planning that increases the service life of buildings and
building systems. Such a premise mandates the design of buildings and building systems
that facilitate the maintenance and renovation process. Current practices do not support
this. There is considerable urgency in moving toward a more sustainable and resilient
building sector, yet the required technology and know-how to accomplish this are largely
unavailable. Pervasive innovation is required throughout the building process, from
design practices to materials, products, and construction methods. Innovation requires
different ways of thinking, questioning the conventional manner of doing things,
consideration of ideas that may seem unrealistic or impracticable.
This chapter explored the consideration, and possible enhancement, of building façade
durability, and assumed a technical focus with the prospect of a largely technical design
and delivery response. Sustainability may be a design problem, but it is an even greater
social problem, as represented by the discussion in section 4.3.6 on the manifestations of
throwaway culture and obsolescence. As noted, building demolition and major façade
renovations are not driven by technical problems such as material degradation, but by
nontechnical and highly subjective forms of obsolescence, often related to attributes of
appearance. Until societies value attributes and manifestations of sustainability above the
arbitrariness of style and fashion, this is unlikely to altar, absent the inevitable press of
necessity forcing behavioral change, which the growing threat of climate change may
deliver. Even here, however, advancements are possible. Burns (2002) notes that, as
obsolescence is inevitable, it must be planned for. Anticipatory planning practices and
embodying adaptive capacity in façade system designs can at least partially offset the

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threat of obsolescence, and provide options to the future generations left to deal with the
many challenges they inherit, options that are apparent by their current absence. These
practices have the added benefit of emphasizing an important building/occupant
symbiosis, leading to longer lasting healthier buildings and more productive work spaces.
Buildings that endure as models of sustainability are buildings that are cared for.

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Chapter 5 — Is glass green? Considering the
Insulating Glass Unit
[Portions from this section were first published in Patterson (2011c) and Patterson et al.
(2014a).]
The insulating glass unit (IGU) is a curtainwall subassembly and a ubiquitous component
of commercial building facades since the 1980s. Alternative means of providing the
functionality of the conventional IGU, while mitigating the undesirable lifecycle impacts
associated with its production, use, and disposal, are possible. Design strategies
developed within this context may be applicable to other façade system components, and
to the façade system itself, and potentially to a broader range of challenges presented by
the built environment.
Specific metrics for durability and recyclability of IGU’s were chosen as development
goals, as these attributes are problematic in conventional insulating glass products. A first
objective is for 100% recyclability of all materials used in the unit design. A second is the
adoption of a perpetual service life; a product that can be renewed as required while
seeing continuous service over an indefinite timeframe. Kesik (n.d.) comments that
building structural systems are engineered to perform for the long term, with precedents
pointing to a typical service life of “several hundred years.” He further remarks that, “the
skins of buildings are ideally intended to last the life of the whole building, in particular
its structure, or skeletal system.” The conceptual IGU is referred to as the millennium
IGU, or m-IGU, in an attempt to shift the service life mindset from decades to centuries
and millennia. These goals are embraced as design constraints that demand a different
way of thinking about the problem of providing a highly insulative glass assembly that
enhances primary attributes of sustainability.

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This is essentially a reductive exercise singling out the IGU, as one weak link in the
façade system, to test the idea that the service life of metal curtainwall systems can be
extended through a renewal strategy incorporating planned maintenance and partial
renovation cycles, thereby providing advantages that improve building sustainability as
compared with a replacement renovation strategy. The intent is a conceptual exercise to
explore abandoning current high-performance glazing strategies that present certain
defined sustainability challenges, and the development of fundamentally new approaches
that could potentially overcome those challenges; a viable concept creates the potential.
There is no intent to develop that concept as a marketable product. The exercise affords
the opportunity of applying the durability attributes discussed in section 4.3 as a critical
review of the IGU, accompanied by alternative solutions that embody those attributes.
5.1 The problem with the IGU
The insulated glass unit and the threat it represents to façade system service quality and
the premature termination of façade system service life, and the accompanying wasted
durability, are discussed in section 4.4.6. The following sections provide additional
context on architectural glass as a precursor to the discussion of alternative strategies in
providing the functionality of the IGU.
5.2 High performance glazings
Selkowitz (2001, 1) and others credit the developments provided by the glass industry—
particularly the advent and application of thin film coatings—with the significant
improvements in solar and thermal performance of highly glazed building facades.
Today’s spectrally selective thin film coatings are most frequently applied to the interior
surfaces of the glass, usually the number 2 surface (surfaces are counted from the outside
in; 1 being the layer of glass in contact with the exterior), and the cavity is often filled
with a gas (i.e., argon, krypton) less conductive than air. These developments are
reflected in center-of-glass U-factor improvements promoted by suppliers ranging from
1.02 with clear single glazing to 0.15 in a high-performance triple-glazed assembly with
low-e coatings and argon gas fill.

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5.2.1 Unintended Consequences
The unintended consequences of these processes and alterations intended to improve
solar and thermal performance are twofold: first, the collapse of service life and wasted
durability, and second, the rendering of the float material as unrecyclable, producing a
negative effect on embodied GWP, and burdening the solid waste stream.
The primary focus of green building has long been reducing energy consumption during
the operational phase of building lifecycle. The widespread application of low-e and
spectrally selective coatings on the surface of IGUs has become a commonplace and
effective solution for high-performance building facades. There are energy efficiency
gains resulting from the solar and thermal control provided by these high-performance
glazings when considering a building’s operational phase (Lee et al. 2002). The still
emerging practice of lifecycle assessment (LCA) has brought growing recognition that
there is more to it than just operational energy considerations (Garvin 1994).
5.2.2 Embodied Energy
Glass is a material with relatively high embodied GWP. The embodied impacts of
architectural glass are comprised primarily of the energy consumed in material extraction,
processing, manufacturing, transport, and installation activities involved in constructing
the building, and also those involved with the end-of-life disassembly, reuse, recycling or
disposal. Added to this are the recurring impacts resulting from repair and maintenance
over the lifespan of the building. Embodied energy and the associated impacts are
becoming an increasingly important consideration of the green building dialogue.
Embodied impacts are discussed in section 4.3.3, and more specifically with respect to
glass in section 4.4.7.
5.2.3 Durability and Service Life
The concept of differential durability recognizes that buildings and building systems are
assemblies typically comprised of subassemblies and components, and that the service
life of any system may be limited to its least durable component. The least durable
component of an IGU is generally the perimeter sealant that provides the hermetic seal of
the cavity (Wolf 1995, 302). The failure of an IGU is most commonly caused by air
leaking into the cavity bringing moisture that results in condensation, fogging, and
oxidation of aluminum and metal oxide coatings, and airborne particulates that result in

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deposits on the interior glass surfaces. Occasionally even mold can develop within the
cavity. While this may not constitute catastrophic failure of the product from a
performance standpoint, it reduces service quality to the extent that replacement is often
implemented for aesthetic reasons, thereby limiting the service life of the product
(Lingnell and Spetz 2007; Golda 2014).
5.2.4 Service Life Collapse and Wasted Durability
Float glass is a remarkably durable material with an indefinite service life in the building
skin that can be measured in centuries. The IGU has an approximate service life of 20-30
years, with a failure curve that begins within the first year and accelerates as the product
ages. The IGU construct, with its lack of repairability and with the seal as the weak link,
effectively collapses the service life of unprocessed float glass from centuries to a few
decades. The reduction in service life in the glass represents wasted durability: latent
durability that goes unrealized.
IGUs are a common component of contemporary unitized curtainwall systems. No
provision is typically made in the design of these systems to facilitate the removal and
replacement of the IGUs. The change-out of an IGU can present a significant challenge;
access can be difficult, and re-glazing a new IGU in place problematic. Consequently,
renovations of curtainwall facades typically involve removal of the existing façade and its
replacement with a new one. It can be seen, therefore, that the seal of the IGU not only
defines the service life of the IGU; it contributes and may ultimately define the service
life of the entire façade.
5.2.5 Recyclability
Float glass is remarkable not only for its durability: it is also a perfectly recyclable
material capable of producing new virgin material at a reduced energy premium over
production from raw materials. But unprocessed float glass is extremely rare in
contemporary building facades. It is occasionally down-cycled (e.g., ground up and used
as asphalt fill or landscaping material) but most often enters the solid waste stream and
ends life in a landfill. It is ironic that the enhancements referred to above—secondary
processes implemented to improve the functionality of the material (coatings, laminating,
insulating)—result in at least an order of magnitude collapse in durability and render the
material unrecyclable. These considerations necessarily broaden the definition of
performance.

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5.3 Design Goals and Assumptions for the m-IGU
The use of high performance glazing products has contributed positively to energy
savings and thermal comfort in buildings, but durability and recyclability are fundamental
sustainability attributes that should not be ignored. Yet the current design of the IGU puts
thermal and solar performance into opposition with durability and recyclability. The goal
here is a conceptual design solution with performance equal to current high-performance
glazing products while using unprocessed float glass, resulting in no compromise to
durability or recyclability of this primary material.
5.3.1 Service Life
The glass industry has been working toward establishing a service life of 40 years for
IGUs. Recently, there has been talk of doubling that goal, certainly an ambitious
undertaking with the current IGU design configuration. The question remains, however,
as to whether even that is adequately ambitious in the context of achieving a sustainable
built environment, especially without a clear solution to the recycling limitations.
Conventional assumptions about durability are commonly inadequate, and doubling the
current IGU service life, while certainly helpful, may undershoot the need as well as the
potential. It reduces but does not dispense with the wasted durability of the current IGU,
and does nothing inherently to establish recyclability of the product. An entirely new
approach may be required if current high-performance systems are to be transformed to
the sustainable systems of tomorrow. Adopting constraints, even seemingly
insurmountable constraints, may sometimes provide the framework for alternative
strategies.
5.3.2 Constraints
The following design constraints are adopted for this exercise:
§ the use of unprocessed float glass.
§ the use of fully recyclable materials.
§ service life – perpetual (1000 years BHAG)

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5.5 Makeup of the m-IGU (Figure 7.1 and 7.2).
The conceptual makeup of the m-IGU is represented in Figures 5-1 and 5-2.

Figure 5.1: Concept sketch for the m-IGU.

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Figure 5.2: Concept sketch for the m-IGU.

5.5.1 Material
Various material components impact the durability of the IGU: glass, spectrally selective
films and coatings, seals and gaskets, and the spacer/cassette framing among them.
Material assumptions and suggestions follow, but should be considered preliminary, as an
evolution of material definitions in response to future research would be expected.
Materials need the capacity to be favorably recycled, and embodied energy must be
evaluated through a comparative LCA process. Even with a smaller relative embodied
energy value, glass is clearly the dominant material comprising conventional IGUs by
virtue of its mass (Table 5.1), increasing the value of its extended service life.

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Table 5.1: Preliminary embodied energy analysis for baseline IGU. Embodied energy values from ICE
database (Hammond and Jones 2011).
Component
Embodied Energy
(kBtu/lb) Weight per SF
Embodied Energy Use
Intensity (kBtu/ft^2)
Glass 10.10 6.00 60.60
Argon 2.92 0.10 0.29
Stainless Steel Spacer 24.38 0.25 6.10
Sealants 26.51 0.20 5.30
Desiccant 0.86 0.20 0.17
Unit total 10.73* 6.75 72.46
*averaged kBtu/lb for IGU assembly
5.5.2 Glass
Annealed or heat strengthened glass is used with the m-IGU, without coatings or
lamination to assure optimal ease of recycling. The use of annealed glass would provide
for greater ease of reuse, as the material could be recut to smaller size to fit a new
application. Thermal stresses may require the use of heat-strengthened glass, which
cannot be cut after heat treatment. In any case, the use of unprocessed float glass, or
minimally processed heat strengthened glass, without the application to the glass surfaces
of coatings, laminates, or sealants, eliminates all technological barriers to reintroducing
the material to the float process for the production of new material, thereby rendering the
glass in the m-IGU fully recyclable.
5.5.3 Films and Coatings
The strategy is to keep the coatings from being applied directly to the surfaces of the
glass lites. Instead, the coatings are applied to a polymer film suspended within the cavity
of the IGU. A precedent for this is the Heat Mirror product, which claims a U-factor as
low as 0.05 for a multiple film application (Eastman 2017). The solar and thermal
improvements result in part from the spectrally selective coatings, and part from the
cavity partitioning provided by the suspended films, similar in effect to a triple or
quadruple glazed IGU, but without the added weight (triple glazed IGUs are 50% heavier
than conventional IGU products) and dimensional thickness resulting from additional
glass layers. Suspended film IGUs were used in the recent renovation of the Empire State
Building (Schneider and Rode 2010).

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5.5.4 Durability Harmonization
In any case, the durability of the film would not limit the durability of the m-IGU
assembly. The film is envisioned as being loaded in a cartridge within the assembly
cavity that can be removed, new film installed, and the cartridge replaced. Thus, neither
the service life nor the recyclability is compromised by the application of a coating to the
glass surface. It is conceivable that coated glass is someday widely accepted by float
producers for reintroduction into the float process. Some claim that thin film oxides
readily burn off from the glass melt, and there are reports that some producers do recycle
coated cullet. Such developments could render the use of coated glass as a viable
consideration supporting the goals of this conceptual exercise. There is, however, still the
problem of the durability of the film limiting the service life of the glass.
5.5.5 New Tech Ready
The suspended film strategy as suggested in the m-IGU has the additional benefit of
readily adopting the advances in material science so frequently produced by industry over
the past three decades. The use of new high-performance low-e coatings could be
accommodated simply by changing out the suspended film cartridge, as opposed to
changing out the entire IGU, or in the case of unitized curtainwall systems, replacing the
entire façade system, a formidable barrier to the adaption of new glazing technology.
5.5.6 Recycling the Chemical Soup
The polymer film with various metal oxide coatings will likely present a recycling
challenge to the chemical industry, but one that should be more manageable owing to the
separation of the coatings from the glass and the material handling benefits thus provided.
However, the viability of this approach as a recycling strategy requires further research.
At minimum, the impact of the coatings has been mitigated through this approach.
5.5.7 Compression gaskets
Wet-applied sealants do not promote ease of maintenance, and are at least part of the
reason that the glass in IGUs ends up as landfill. Therefore, compression gaskets are used
as an alternative means to provide the seal for the m-IGU. The dry gaskets accommodate
the partial disassembly and reassembly of the m-IGU for maintenance purposes.

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5.5.8 Cassette frame
1. The cassette frame is key to the m-IGU. It combines the primary functions of
spacer between the glass lites, replacing the conventional IGU spacer, while also
providing a minimal frame designed to facilitate the installation and removal of
the IGU from a curtainwall unit.
2. The cassette frame provides the following functions in sum:
3. separates the glass lites to create the air cavity using an integral suspended film
cartridge.
4. holds the compression gaskets that provide the seal to the glass lites, thereby
sealing the cavity between the lites.
5. holds the pressure equalization filter that links the cavity to the ambient
atmosphere.
6. holds the suspended film(s) cartridge with spectrally selective coatings.
7. accommodates partial disassembly for maintenance of the interior cavity and
components.
8. facilitates the installation and removal of the entire assembly within a curtainwall
module.
5.5.9 Material
The cassette frame is conceived as an assembly built up from extruded, coextruded, or
pultruded plastic rails. Various adhesives are available to join the framing members at
their corners. Plastics provide the advantage of low thermal transfer, the reason for their
application as thermal breaks in the aluminum extrusions that comprise conventional
curtainwall units. The use of thermoforming plastics would present advantages in
material recyclability. Multiple material types can be configured within the same section
using a co-extrusion process as a means to optimize performance attributes. Alternately,
wood or bamboo could be considered as a low-impact framing material, perhaps as part
of a composite assembly that incorporated more moisture resistant materials in surfaces
directly exposed to the exterior environment or at likely areas of condensation.
5.5.10 Mechanisms
The cassette frame incorporates two important mechanisms not developed as part of this
conceptual exercise. The first compresses the seals between the glass and the spacer
component (suspended film cartridge) of the frame, and is indicated in the sketch (Figure

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5.1) as a perimeter capture that screws into the frame. It is also easily conceived as
discontinuous clamp plates screwed to the frame with a snap cover plate. More elaborate
mechanisms are certainly possible, like a hinged-frame subassembly for the inboard lite
that would allow easy opening of the IGU assembly and could facilitate ease of interim
maintenance. The benefits of a more elaborate approach to further ease maintenance
processes must be balanced against added cost, complexity, and embodied impacts.
The second mechanism provided by the cassette frame facilitates the primary cassette
function: the easy installation and removal of the IGU assembly within a modular unit of
the curtainwall system. One of the significant shortcomings of contemporary curtainwall
systems is the challenge presented by post-production removal and installation of an
IGU, potentially limiting service quality, and even service life of the curtainwall system,
to that of the IGU. Cassette strategies afford the opportunity to adopt new glazing product
developments without the need to replace the entire façade system. This is a desirable
attribute as the development of higher performing products accelerates and the uptake of
these emergent products becomes vital to increasing the performance of the building
sector. While other design strategies are possible, one precedent is found in the use of
toggle glazing systems, in which a toggle mechanism is used to fix the IGU within the
curtainwall framing systems (Kawneer 2017). In this concept, the cassette frame could
facilitate a toggle connection between the IGU and the curtainwall module into which it
is fitted. A gasket seal would also be required between the cassette frame and the
curtainwall unit as indicated in Figure 5.1.)
5.5.11 Resilience Attribute
The ability to change out an entire m-IGU assembly with relative ease and rapidity is an
important resilience attribute. Storm damage to the glass caused by high wind or impact
from airborne debris, or manmade damage resulting from forced entry or vandalism, can
be quickly replaced with relative economy. In comparison, IGU replacement in
conventional curtainwall systems will typically require the complexity of façade access
from outside the building, and present a removal and replacement challenge depending
upon the curtainwall unit design, which typically fails to anticipate this eventuality (Brian
and Wills 2002).

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5.6 Vented Cavities in Façade Systems
Hermetically sealed unvented cavities are the standard in IGU products. Earlier
researchers explored the potential advantages of a vented IGU cavity (Ambrose and
Karagiozis 2007). As a precedent, vented shadowbox constructs are used in
contemporary curtainwall systems in spandrel areas. The practice is controversial, with
some designers preferring the use of unvented variations (Boswell and Walker 2005).
The biggest problem with vented shadowboxes is the lack of easy access for cleaning if
moisture and particulates in the cavity negatively affect the appearance of the façade. The
debate takes place with the assumption of zero-maintenance. Maintenance access to the
spandrel area is complicated by the floor slab, mechanical systems, and interior finishes
that typically occupy this zone. Setting the aesthetics of the all-glass façade aside, the
spandrel area is an excellent opportunity for a highly insulated, low maintenance, rain
screen panel system. This would lower the window-to-wall ratio, affording the benefit of
an improved façade system U-factor and providing enhanced building resilience and
energy efficiency.
5.6.1 Consideration of a Vented IGU
The advantages of a vented IGU include
§ the elimination of pressure differentials significantly reduces stresses on the
cavity seals, virtually eliminating the likelihood of the seal discontinuities that
compromise service quality and service life.
§ elimination of visual distortion in the IGU caused by the bowing—or
“pillowing”—of the IGU resulting from the pressure differential inside and
outside the cavity (Figure 5.3).
§ pressure equalization cycles allow any moisture that enters the cavity to dry out.
These are significant advantages. The reduced stresses applied to a pressure gasket
approach, as proposed with the m-IGU, diminishes the importance of the cavity seal;
even if there are minor discontinuities in the seal, the air exchange is designed to occur
through a filtered port, minimizing the potential for lasting effects like trapped
condensation and particulate deposits on the glass, which, in any case, are easily removed
through routine maintenance procedures.
The pillowing characteristic of a conventional sealed-cavity IGU results in an optical
effect in the exterior glass, an often pronounced visual distortion of reflections from the

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glass surface that is frequently objectionable to the building designer and owner (Figure
5.3). The sole option to mitigate this affect is to employ a thicker glass lite (i.e., 9mm
instead of 6mm) for the outboard lite of the IGU, certainly an undesirable practice from a
sustainability and cost perspective. This phenomenon would be eliminated with a vented
IGU.

Figure 5.3: The effects of IGU pillowing are apparent in the reflection of the building (left) in the glass
façade (right).
5.6.2 Gas Fills
A vented cavity prevents the use of low conductivity gas fills like argon and krypton
commonly used in high-performance glazing products, but the m-IGU also eliminates the
need for such gases, as effective U-factors are achievable without them. Durability is
enhanced in the process, as the performance of the gas fill is easily compromised by
minor discontinuities in the hermetic seal of an IGU.
5.6.3 Cavity Ventilation Filter
Cavity ventilation is actualized through a filtered port to outside air (Figure 5.2). The
filter material and the size of the port are important design considerations to be
determined in future development. The port size should be just large enough to facilitate
pressure equalization. The filter should accommodate air passage while trapping
particulates and blocking moisture. There are a number of material options for this
application with varying behavioral characteristics. Accelerated environmental testing of
a mockup or prototype will likely be required to determine the optimally suited material.

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The filter would be designed for easy removal and replacement from within the building.
The used filters should have the capacity to be cleaned and reused, or recycled,
depending upon the filter material employed.
5.7 Maintenance as a Strategy for Renewal
Order of magnitude service life increases demand a reevaluation of maintenance as a
strategy for renewal and regeneration, but maintenance has its own impacts that must be
considered.
5.7.1 Minimizing the Impact of Maintenance
A renewal strategy previously diagrammed in Figure 4.13 allows for maximizing the
service life of each component within a system. Maintenance is evaluated in LCA as
recurring embodied energy, and adds to the lifecycle embodied energy debt of a building.
Analysis is required to investigate the tradeoff between increased durability and recurring
embodied energy. Design and planning are required to harmonize component service life
and facilitate maintenance requirements.
Maintenance can also enhance system performance, however, resulting in improved
operational energy efficiencies. The aging of air and water seals in unitized curtainwall
systems certainly has the potential to compromise performance. Identifying and
remedying such a problem presents a considerable challenge, as the seals are concealed
from inspection, and impossible to repair in any case. If such systems are to be designed
for durability, seals must be easily inspected and replaced as required. The same must be
true of the components that comprise the façade system, thus the IGU must incorporate
seals that are accessible and replaceable.
The maintenance strategy with the m-IGU:
1. balance maintenance requirements to maximize service life while minimizing
recurring embodied energy,
2. facilitate ease of maintenance through product design,
3. focus on minimal maintenance provided on an as-needed basis, and
4. maximize the lifespan of each component within the assembly to minimize the
effect of differential durability.

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The actual maintenance requirements for the m-IGU are the most critical unknown, so a
conservative approach has been taken in their accommodation. While mechanisms are not
detailed, strategies for both incremental maintenance and complete unit replacement have
been incorporated, although the incremental maintenance holds the potential to render the
complete unit removal an unnecessary redundancy. Unlike conventional IGUs and
curtainwall systems, all component parts are intended for easy inspection and
replacement, most especially those critical to performance and/or subject to wear, or
simply of lesser durability, as with the various seals and suspended films.
5.7.2 Ease of maintenance: Access
The assembly is to be designed so that all maintenance procedures can be actuated from
inside the building, avoiding the necessity of accessing the façade from the exterior, a
generally favorable attribute with high-rise buildings. Maintenance access is provided
through the temporary removal or displacement of the inboard lite. Only the replacement
of the outboard lite and the inspection and replacement of the seals between the cassette
frame and the curtainwall unit may require the removal of the entire assembly.
Alternatively, the procedures could conceivably be designed to carried out from a
window-washing rig.
5.7.3 Frequency of maintenance
Planning procedures like maintenance and service life planning (SLP) aid in anticipating
the timing and magnitude of repair, maintenance, retrofit and renovation requirements.
Minimal maintenance is the goal, but frequency of the maintenance cycles is a critical
unknown, e.g., how often the units have to be opened up for cleaning. The pressure
equalization filters can be designed for easy servicing, but the removal or displacement of
the inboard light, cleaning, inspection, and reassembly would be more invasive.
Procedures and equipment could be designed to optimize the process. IGUs, for example,
can be quite large in contemporary facades, particularly large residential and commercial
buildings. This could present a challenge to the maintenance program envisioned herein.
Figure 5.4 shows a concept for a simple semi-automated device that facilitates the
removal, installation, and cleaning of either the inboard glass lite for cleaning of the IGU
cavity, or the removal of the entire IGU cassette. The device accommodates local
maintenance procedures or the transport of the inboard lite or the entire IGU cassette to a

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specialized maintenance area. SLP affords the opportunity to maximize the efficiency of
maintenance procedures, reducing the recurring embodied impacts.

Figure 5.4: A conceptual semi-automated device to aid in the maintenance of the m-IGU by
facilitating the removal of the inner lite, or alternatively, the entire unit if required. (Advanced
Technology Studio – Enclos)
5.8 Integrated design and planning processes
Buildings have rarely been evaluated over lifecycles of the proposed timeframe.
Recurring patterns of maintenance will define recurring embodied energy over the
building lifecycle. Comparative analysis can then be undertaken with variations in
maintenance and renovation cycles, including a zero-maintenance strategy that models
complete façade replacement on a periodic basis.
An integrated design development process would utilize LCA, lifecycle costing analysis
(LCCA) and SLP to provide an optimal environment to guide decision making during the
development process. LCA would provide input on and guide material selection to
minimize embodied carbon impacts. SLP would determine the service life and related
repair, maintenance, upgrade and renovation requirements over the design service life as
inputs to the LCA mode. LCCA would be used in parallel to these processes to provide
feedback on the economic impact of decisions through design development. It is
seemingly inevitable that the m-IGU will be more expensive than a conventional IGU on
a first-cost basis. Institutional building owners and other owner-occupiers are more
amenable to a lifecycle perspective, but they are likely to be challenged by a lifecycle

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measured in centuries. Yet it is conceivable that this is what the evolution of a sustainable
built environment will demand.
5.9 Conclusion
A framework for a conceptual prototype has been proposed for an IGU that fulfills
stringent sustainability goals. Design constraints include the use of unprocessed float
glass, fully recyclable materials, and a service life measured in centuries. Initial proposals
for material selection for glass, films and coatings, compression gaskets, the cassette
frame, and the treatment of the cavity are outlined. An integrated design development
process is outlined including LCA, LCCA and SLP in support of an ongoing process of
renewal the perpetuates the service life of the IGU indefinitely.
There are certainly other viable approaches to solving the problems highlighted here.
Industry, for example, could provide technical solutions for recycling glass, and new
fabrication techniques dramatically improving IGU seal durability. This conceptual
exercise with the m-IGU is intended to:
§ exemplify the issues discussed in section 4.4,
§ demonstrate alternatives to entrenched practices,
§ and support the hypothesis that renewal strategies embracing planned
maintenance can potentially extend service life behavior of metal curtainwall
systems, providing advantages as compared with current practices.
Constraints drive innovation (Hoegl et al. 2008; Moreau et al. 2005; Goldenberg et al.
2001). The embrace of constraints involving durability and recyclability can drive novel
solutions to entrenched problems. A service life goal of 100 years, coupled with an
approach of incremental improvements along the same design trajectory embodied in the
contemporary IGU, did not seem enough. It still left significant wasted durability of glass
and aluminum. The commitment of resources represented by the building sector demands
a level of responsibility in the application of these resources that has yet to be confronted
in current practice. Considerations of cultural resilience and sustainability will eventually
comprise a context where such sensibilities become not only compelling but also
mandatory. It can certainly be argued that the various forms of obsolescence must
necessarily render any discrete building obsolete long before the proposed service life

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goal. If buildings are designed to adapt to the evolution of occupancy and use as
suggested by Brand (1994), then this impact could be minimized, yielding buildings not
only designed for longer service life but to facilitate adaptability. The m-IGU is a
conceptual response to the technical issues of material degradation, already identified as
seldom the determining factor in service life. However, it also radically enhances the
adaptability of the façade system, the best hedge against future obsolescence.
The development of conceptual solutions supporting a theoretical order-of-magnitude
increase in service life by strategically accommodating planned cycles of maintenance
and partial renovation as demonstrated with the m-IGU, while not conclusive, supports
the first part of the hypothesis in Section 2.2, that “the service life of metal curtainwall
systems can be extended through a renewal strategy incorporating planned maintenance
and partial renovation cycles. In addition, different ways of thinking about the problem
may be revealed in the face of imposed constraints. The strategy was to target one
specific façade subassembly as a vehicle to test the development of such a conceptual
solution. The exercise effectively highlights the problem of bonded assemblies; unbonded
assemblies possess far more adaptive capacity and are more easily designed to facilitate
repair, maintenance, retrofit and renovation requirements. The conceptual exercise with
the m-IGU clearly demonstrates that embracing constraints can drive novel solutions.
This is, however, an uncommon practice in modern society. Quite the opposite is true;
massive resources are spent fighting against any imposed constraints or regulation,
largely as a means of protecting the vested interests of powerful industries and
organizations. This is a significant barrier to the development and adoption of innovative
solutions needed in the pursuit of a sustainable built environment. An example can be
found in Europe in the wake of the 1970s-energy crisis, where legislative mandates for
deep cuts in building energy consumption drove European façade technology two
decades ahead of that in North America, which still lags in both technology and
applications. Breakthrough design solutions to the challenges of sustainability are
achievable, but their development and adoption unlikely, or at best significantly hindered,
in the absence of aggressive policy formulation by an enlightened leadership. Short term
prospects in this regard are not favorable.
Renewal and Regeneration vs. Service Life
The 1000-year goal started out as deliberate hyperbole, but as the consideration of this
concept progressed, it suggested interesting conceptual approaches to aligning differential

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durability through maintenance strategies. In a sense, the approach adopted for the m-
IGU renders the concept of a service life at the scale of building and major building
assemblies obsolete, replaced instead by a renewal process that results in perpetual
regeneration. An m-IGU may still be operational 1000 years out, while not containing
one component from the original assembly. Yet the assembly was never out of service.
The regeneration process fully embraces the notion of the circular economy as a closed-
loop system with zero waste. Here this regenerative strategy is applied to a singular but
ubiquitous glass product, but the same concept can be translated to the façade system, and
even to the building itself.

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Chapter 6 — Supple Skins: A Methodology and
Framework for Considering Façade System
Resilience
[Portions from this section were first published in Patterson (2014d) and Patterson et al.
(2014b; 2016; 2017).]
6.1 Introduction
Resilience is currently the predominant buzzword in the green building lexicon.
Resilience has been referred to as the new green and the successor of sustainability,
among other things, and has spawned a movement coming into increasing prominence in
the wake of hurricane Sandy and its dramatic impact on New York City and surrounding
areas along the eastern seaboard. Much of the resilience dialogue centers on what
happens during and immediately following a natural disaster, or what can be categorized
as hazard mitigation, risk assessment, and recovery.
Resilience has been usefully adopted and developed as a core concept within different
disciplines ranging from many of the sciences to business management, many of which
are explored here as part of prior work. The brand of resilience that is the specific subject
of this research is referred to herein as urban resilience, as it concerns the resilience of
buildings and the built environment and is principally, but not exclusively, the domain of
city governance.
The building façade—in its critical role as mediator between nature and the indoor
environment—is frequently referenced in the resilience dialogue, but limited to the most

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obvious considerations of storm generated extreme winds and accompanying airborne
debris, or the desirability of the of the façade to facilitate passive ventilation under certain
conditions. Term roots, however, reveal that the underlying theories of resilience are
nuanced—particularly those stemming from ecological science—and there is value in
exploring the subtleties of the concept.
Prior work is therefore explored with the intention of establishing:
§ fundamental principles of resilience;
§ how these principles have shaped, or been ignored by, the current resilience
dialogue;
§ and a relationship between resilience and sustainability.
This provided a basis for the development of survey questions and a workshop designed
to explore resilience and the building skin among a cross section of façade industry
professionals, this as a means to better understand current perceptions of resilience and to
further explore concepts of resilience for relevance within the particular domain of the
building skin.
The outcome was the establishment of clear linkages between resilience and the building
façade. These linkages are then used in the development of a framework for the
evaluation of façade resilience, including the consideration of enhancements with the
potential to improve the resilience not only of the façade system, but also of the
encompassing building and urban habitat.
The results of this research are reported following. The findings are used to develop
principles of façade resilience, as well as a set of primary considerations as façade
resilience factors. A methodology is then presented for developing and organizing this
research using these resilience factors as a categorization scheme. The final product is a
table that organizes resilience factors, and couples them with related metrics and potential
strategies for enhancing façade resilience.
6.2 Bending Strength
The bamboo that bends is stronger than the oak that resists. – Japanese Proverb

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As highly glazed facades began their rise to prominence back in the 1970s, the engineer’s
inclination was to develop a stiff structural system that would minimize the stresses of
movement on the glass. But the press for higher transparency in the building envelope
was at odds with the materiality of these deflection resistant structures. This led to
experimentation with tensile structures and the development of glass systems to
accommodate the large deflections characteristic of this structure type. The advantages of
structures designed to accommodate considerable movement were soon recognized. Like
the stringed web of a tennis racket, a cable net façade is able to absorb the energy of wind
gusts through deflection and recovery. Increasing the resistance to these deflections
increases the stresses to the structural system. Structures capable of accommodating high
deflections have proven to have advantages in extreme loading conditions, including blast
and high impact events. Deflections must be controlled, of course, and the capacity to
resist is the essence of structural design, but resilience is a complimentary attribute that
brings important enhancements to engineering practice.
In engineering terms, resistance is to oppose, and resilience is to bend. Socially,
resilience is about change. Not the ability to resist change, but the capacity to adapt in the
face of changing conditions. Not an unrestrained abandonment to the forces of change,
but a calculated release of the familiar as a means to preserve the essential. Both of these
perspectives and many others manifest in the current urban resilience dialogue.
Resilience is the capacity to adapt to changing conditions and to maintain or
regain functionality and vitality in the face of stress or disturbance. It is the
capacity to bounce back after a disturbance or interruption of some sort.
(Resilient Design Institute, 2013)
Buildings can be designed to resist hurricane wind loads, but disaster resistance is not the
same as disaster resilience. Practitioners have learned to design buildings that resist, but
have more to learn about designing buildings that bend. As Zolli (2012) points out,
Lower Manhattan is a newly developed area dense with the latest crop of LEED rated
high-rise buildings, which by all rights should have performed well in the wake of
hurricane Sandy. Instead it was among the hardest hit areas of the region. The problems
may start at the infrastructure scale with flooding and power outages, but the impact is
ultimately to buildings and their occupants, and these impacts suggest there may be
things missing from the point spread of the building rating system.

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“Bounce back” is a term that is often used in the resilience dialogue across disciplines,
referring to the time for a system to return to the initial state (or something close to it)
after having experienced a disturbance. Resilience, however, is also frequently discussed
in terms of the response to “shocks and stresses,” which introduce a temporal nuance to
the causal events; shocks are characterized by high impact and relatively short duration,
typically measured in seconds (e.g., earthquake, bomb blast) to days (e.g., hurricane,
temperature extremes), whereas stresses often build up over longer timeframes (e.g.
extreme drought, economic recessions). Both shocks and stresses can produce
consequences that result in extended periods of recovery, but the long duration stresses
are more subtle in effect than shocks, and capable of producing unanticipated outcomes.
6.3 Resilience in the Public Sphere
Resilience may be that latest buzzword, but what is its place within the pantheon of the
green building vocabulary? Interestingly, sustainability and resilience are often set in
contrast to each other in mainstream media, with the implication that sustainability is out
and resilience is in—Forget Sustainability. Its About Resilience, for example, was the
Internet byline for an op-ed piece on resilience in the New York Times by Andrew Zolli
(2012). Such a position fails to differentiate between sustainability and resilience—they
are not commensurate terms—and to recognize the important relationship between the
terms. In fact, strategies to achieve resilience can run counter to sustainable construction
practices, and sustainable strategies can ignore considerations of resilience, thereby
ultimately compromising their very objective. While not commensurate, there is a
complimentary relationship between the concepts. Resilience, while long ignored in the
sustainability dialogue, is a necessary attribute of sustainability, and one of the strands of
sustainability developed in [cref chapter]. Brian Walker, a Research Fellow with CSIRO
Sustainable Ecosystems and former Program Director and Chair of the Board of the
Resilience Alliance, an international research group working on sustainability of social-
ecological systems, has this to say about the relationship between sustainability and
resilience:
The bottom line for sustainability is that any proposal for sustainable
development that does not explicitly acknowledge a system's resilience is
simply not going to keep delivering the goods (or services). The key to

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sustainability lies in enhancing the resilience of social-ecological systems, not
in optimizing isolated components of the system. (Walker and Salt 2006, loc
206-208)
Referring here also to the reductionist practice of breaking complex systems into discrete
parts, then focusing on optimizing the efficiency of select pieces, a practice with strong
tendency to strip system resilience. (Resilience thinking and the issue of efficiency versus
redundancy is further explored in 6.5.1) Walker also points to the value that the resilience
dialogue has brought to the pursuit of sustainability:
The debate on sustainability has come a long way in recent decades. But if we
examine it through a resilience lens, it's clear that we still have a way to go.
(Walker and Salt 2006, loc 208-209)
Another significant aspect of the emerging resilience dialogue is its indication of a focal
shift from taking action to prevent climate change, to a tacit acknowledgement that the
effects of climate change are here now, and that the pressing need is to anticipate and
prepare for what is to come, thereby moving from solution mode to response mode. This
is an alarming development to some; among them many of the sustainability activists that
have directed their efforts at mitigating climate change through the reduction of carbon
emissions. The focal shift to climate adaptation is a necessary and pragmatic response,
however. Climate change experts have warned that some degree of climate change will
occur even if greenhouse gas emissions were to be rapidly reduced. The U.S.
Environmental Protection Agency (EPA 2014), the Intergovernmental Panel on Climate
Change (IPCC 2014, 40), the U.S. Global Change Research Program (USGCRP)
(Bierbaum, R, et al. 2014, 671), and others, have advised that climate change impacts are
now inevitable, and that considering the causal role of human behavior in climate change,
the degree and types of impact are uncertain. A U.S. Green Building Council (USGBC)
report concludes:
As green building professionals, we need to understand the probable impact of
climate change on the built environment and to incorporate appropriate
adaptation strategies into our practices so that the environments we design,
build, and manage today will be suitable for a range of uncertain futures.
(Larsen et al. 2011, 6)

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Climate considerations have long been integral to building design. But resilience requires
a fundamental shift in perspective; instead of designing on the basis of historical data, it
is necessary to anticipate emerging conditions and “uncertain futures.” The recognition of
“uncertainty”—not uncommon in the urban resilience dialogue—points to the potential
relevance of considerations beyond the linear, predictive assessments of conventional risk
analysis. And yet it is just these predictive considerations of resistance and recovery in
the face of disruption that dominate urban resilience dialogue and practices.
Nonetheless, the general concern of urban and community resilience has gained
enormous traction in the public dialogue. Sustainability has been a tough sell; the notion
is conceptually complex and the issues abstract; you cannot see greenhouse gasses in the
atmosphere. Scenarios projected out to 2050, or even 2030, are removed from a reality
shaped by the day-to-day existence of most people, and fail to engage with any kind of
substance. Society’s limited ability to consider the needs of future generations is evident
in the problems that now threaten civilization: climate change, resource scarcity,
desertification, and so on. Humans have certainly demonstrated the capacity for foresight,
but struggle with change that occurs over longer timeframes, such as the gradual decay of
infrastructure (Gunderson and Hollings 2002, loc 636), and some researchers question the
adaptive capacity of socio-ecological systems to respond to the rate and magnitude of
challenges presented by climate change (Berkes and Jolly 2002; Adger, Dessai et al.
2009; Dow, Berkhout et al. 2013).
In contrast, the threat of natural and manmade disasters has become increasingly
substantial as the frequency and impact of such events has risen significantly over recent
years. Mass media, while reluctant to even mention climate change, feeds on disaster,
bringing a very high profile to these events and a strong emphasis to the threat they pose.
The perceived threat drives the rapid uptake and widespread traction of the resilience
concept in the evolving green dialogue, bringing a new dimension to that conversation
and broadening its reach beyond the usual constituents. Resilience planning already
ranges from the federal government to municipalities, and even building owners.
So resilience in this emerging dialogue revolves around disaster. The National Academy
of Sciences (2012), with the financial backing of various agencies of the federal
government, has produced a report titled: Disaster Resilience: A National Imperative.
The report defines resilience as, “…the ability to prepare and plan for, absorb, recover

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from and more successfully adapt to adverse events,” and goes on to elaborate:
“Enhanced resilience allows better anticipation of disasters and better planning to reduce
disaster losses—rather than waiting for an event to occur and paying for it afterward.”
While terms such as absorb and adapt reflect recognition that resilience may be more than
simply mitigating the immediate risks and minimizing recovery time, practice remains
tightly focused on predictive risk assessment, mitigation, and recovery. This is not at all
to imply that such considerations are not relevant or important; they are integral to a
robust concept of urban resilience, but one that must equally integrate broader
considerations presented by uncertainty, unpredictability, and the non-linear responses of
complex systems under stress.
Resilience in the social sciences is measured in part by the ability of a social structure to
adapt to changing conditions. These systems can be quite resistant to change, requiring
great stress concentration before a change response is initiated. The higher the stress, the
greater the potential resulting disruption as the system reorders. While the notion of
intellectually calculated incremental adaptation as a means to provide a smooth transition
through periods of state change is a nice idea, it is generally the press of necessity and not
rationale that initiates change. This is evident with the consideration of sustainability and
the implications of such things as population growth and greenhouse gas emissions.
These have been well-documented threats for over forty years, yet little has been
accomplished in implementing responsive change. The reasons for this are complex
(Adger et. al. 2009, 335). Some speculate that the issues involving climate change are
simply to abstract to elicit an appropriate response.
The issues involving urban resilience are far less so. Severe storms pounding the eastern
seaboard, flooding coastal communities, immobilizing transportation networks,
disrupting critical energy and water distribution and waste handling systems—disasters
measured in human lives and property damage through the equally relentless pounding of
networked media—are far less of an abstraction than the problems resulting from the
persistent pumping of invisible gases into the atmosphere. Economic impacts are a
particularly effective pressure point bearing across social scales of community, region,
and nation by the developing effects of climate change.
The National Oceanic and Atmospheric Administration tracks the occurrence of
weather/climate related disasters resulting in damages of over $1 billion (Smith et al.

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2013). Results for 2013 have yet to be reported at the time of this writing, but 2012
included 11 events for a total of $114.6 billion, economic pressure that garnered
considerable attention. (In comparison, the President’s 2012 budget request for the
Department of Education was $77.4 billion.) Hurricane Sandy is among the 2012 events,
accounting for well over half of the cost at $65 billion, and it was Sandy that has fueled
the resilience movement. But Sandy was not the sole culprit in a climate of escalating
shocks and stresses. The ongoing U.S. drought and heatwave tallied $30 billion, and
while the drought has moderated in some areas of the nation, it has deepened in the
southwest, which is experiencing consecutive years of record low rainfall and extreme
drought conditions.
While many environmental and social impacts may go ignored or unnoticed, economic
impacts and loss of life draw widespread attention. This may lend the resilience dialogue
the traction needed to drive social change in a manner that sustainability could not. The
disaster resilience focus on costs to society and threats to human health and key life-
supporting infrastructure may engage planning, policy, and funding strategies at a far
broader scale than has been achieved through sustainability initiatives. FEMA
Administrator Craig Fugate speaking on resilience at an event in early 2012 reflected this
economic impetus (Rainwater et al. nd):
We cannot afford to continue to respond to disasters and deal with the
consequences under the current model. Risk that is not mitigated, that is not
considered in return on investment calculations, will often set up false
economies. We will reach a point where we can no longer subsidize this. –
Craig Fugate, FEMA Administrator
Climate related problems are not the only measure of resilience. Other sources of disaster
range from seismic events to solar flares. Climate related problems extend beyond the
shocks of super-storms; long term stresses like food shortages resulting from extended
draught may result in political turmoil, social unrest, and acts of terrorism that can disrupt
the supply of water, electricity, fuel, medicine, and other essential resources. Resource
scarcity, cost volatility, and supply disruptions resulting from aging and overstressed
infrastructure can have equally troublesome impacts. These things are the impetus for the
expanding resilience discourse. How these considerations manifest in the design of
buildings and building systems is the issue.

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6.3.1 Resilience versus Sustainability
The emergence of new buzzwords in the vernacular is often regarded with some
cynicism—some few stick, many do not. Occasionally a term arises that fuels the
dialogue and affords the opportunity to explore anew and bring new relevance, if not
meaning, to ancillary terminology. Such is the case with the emergent green dialogue
having resilience as its engine. But has the substance of the green dialogue changed, or is
it just a shift in focus? Alex Wilson (2011), founder of the Resilient Design Institute,
remarks:
It turns out that many of the strategies needed to achieve resilience--such as
really well-insulated homes that will keep their occupants safe if the power
goes out or interruptions in heating fuel occur--are exactly the same strategies
we have been promoting for years in the green building movement. The
solutions are largely the same, but the motivation is one of life-safety, rather
than simply doing the right thing. We need to practice green building, because
it will keep us safe--a powerful motivation--and this may be the way to finally
achieve widespread adoption of such measures.
The emerging resilience discourse is the same in substance as the ongoing sustainability
dialogue, but viewed through a lens of life-safety, a nonetheless significant shift that
brings new relevance and vitality to the conversation and enhances the potential for
significant broad-based and diverse uptake within organizations and communities.
However, to drive the needed transformation of the built environment in pursuit of
resilience, the concept must ultimately be interpreted within the urban context at greater
depth than it has to date.
6.4 The Larger Context
The term resilience in this application – like the term sustainability – has roots in
ecological science and systems theory dating back to the 1970s. The concept grew largely
out of studies into ecosystem and species population stability and related research.
Holling (1973) discusses resilience with respect to ecological systems, and in a later
paper differentiates between engineering resilience and ecological resilience, discussing
these terms in the same context as sustainable development (Holling 1996). The concept

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of sustainability was developing essentially in parallel with that of resilience, but
sustainability moved to the forefront in the form of sustainable development, a term
popularized by the 1987 Brundtland Commission of the United Nations, and referring
broadly to the endurance of human life on planet earth (WCED 1987). Resilience, in
comparison, has only come into widespread use relatively recently.
Holling (1996, 33) discusses these two very different notions of resilience, relating them
to fundamentally different aspects of stability. Engineering resilience is the more familiar
in the building arts, in which disturbances relative to a steady state of equilibrium are
resisted, and mitigated by the rapid return to the equilibrium state. This type of resilience
is characterized by “efficiency, constancy, and predictability,” and represents the
conventional linear, causal, positivist, quantitative, predictive interpretation of science
embraced by many disciplines including physics, ecology, economics, psychology, and
sociology.
Ecological resilience, in contrast, is characterized by “persistence, change, and
unpredictability,” where multiple stability domains may exist, with disturbances
triggering jumps between these domains. Here, resilience is measured as the capacity of a
system to absorb disturbances without losing its fundamental character. Berkes and Folke
(1998, 12) claim this to represent a “fundamentally different view of science;” one where
causation and prediction are not a simple matter of formula or deduction, “Rather,
systems are seen to be complex, non-linear, multi-equilibrium and self-organizing; they
are permeated by uncertainty and discontinuities.” They attribute “The beginnings of a
new ‘science of surprise’” to Holling (1986), who identified underlying patterns to
unexpected changes and their impacts to ecological resources (Berkes and Folke 1998,
11).
While paradoxically different, both of these basic definitions may be applicable to the
built environment, somewhat as a function of scale. Engineering resilience is most
familiar and evident throughout the physical scale of building system, building, and urban
habitat, manifesting predominantly as life-safety issues within the context of extreme
events whether of natural or manmade causality—disaster behavior with the measure
being the extent of the loss of function and the time it takes to restore that function. The
National Institute of Building Sciences has this to say:

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In addition to protecting the lives of building occupants, buildings that are
designed for resilience can absorb and rapidly recover from a disruptive event.
Continuity of operations is a major focus. (NIBS 2014)
The focus here is obviously on response to a shock produced by a disaster related event.
“Bounce back” is a term that is often used in the resilience dialogue, referring to the time
for a system to return to the initial state (or something close to it) after having
experienced a disturbance. Resilience, however, is frequently discussed in terms of the
response to both “shocks and stresses,” (Adger 2000, 361; Smith and Stirling 2010; 100
Resilient Cities 2015) which introduces a temporal nuance to the causal events; shocks
are characterized by high impact and relatively short duration, typically measured in
seconds (e.g., earthquake, bomb blast) to days (e.g., hurricane, temperature extremes),
whereas stresses often build up over longer timeframes (e.g. extreme drought, economic
recessions). Both shocks and stresses can produce consequences that result in extended
periods of recovery. This introduces an important consideration of temporal scale to the
concept of resilience.
It is possible that considerations of resilience in the built environment extend beyond the
boundaries of engineering resilience and into the realm of ecological resilience. Ecology
is a term coined by Haeckel in 1878 in response to an emerging area of scientific inquiry
related to the complex interactions of biological species (Park 1936, 3). Biology at this
time was treated as a closed system, separate and isolated from human activity. Park
introduced the concept of human ecology as differentiated from biological ecology, while
noting the links to economy, population, technology, culture, and the environment
(natural resources) (Park 1936, 15). These linkages continued to develop and expand
through the works of such diverse authors as Odum (1971), Fuller (1969), Meadows
(1972, 2008), and others, including Holling. Berkes and Folke (1989, 9) point back
through this line of inquiry and identify the evolution of a systems-based holistic view of
these various linked components that they refer to as an ecosystem perspective, but an
ecosystem that–unlike biological ecology–explicitly links the realms of human society
and ecology, noting that this perspective is consistent with the relationship between
traditional societies and the environment:

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With a few exceptions, including the Western industrial societies of the last 400
years or so, human societies have generally regarded themselves as part of
nature and not separate from it.
They express the view that social and ecological systems are implicitly linked, with any
delineation “artificial and arbitrary” (1998, 4). Holling, Gunderson and Ludwig (2002,
loc 254) continued this line of inquiry with the development of an integrative theory of
change they termed panarchy, a framework for evaluating evolving complex human and
natural systems with multiple interconnections, a framework they see as fundamental to
the identification of risk and vulnerability. More current manifestations along this
important trajectory of interdisciplinary research—and understanding of the interplay
between man and environment—have produced the concept of coupled human and
natural systems (CHANS). CHANS continue the notion of an integrated framework for
the study of inherently inseparable natural and social systems (Liu, Dietz, Carpenter, et
al. 2007; Turner, Kasperson, Matson, et al. 2003).
This concept of human ecology has thus evolved and branched in response to the
embrace of a wide range of disciplines including geography, economics, psychology,
sociology, anthropology, and others, into fields of socio-ecology, socio-biology, cultural
ecology, anthropological ecology, socio-technology, and so on. The shared theme is the
study of the complex interactions and interrelationships occurring at the interface
between human and natural systems. Interestingly, in the same general timeframe that
Holling was developing key concepts of resilience in ecological systems, Palo Soleri
(1973) coined the term Arcology—drawing inspiration from the intersection of
architecture and ecology—for his concept of high density mega structures as an optimum
form of human habitat. More relevant to the consideration of contemporary urban habitat,
perhaps, is the branch of human ecology that has developed as urban ecology (Burgess
2008; Pickett, Cadenasso, Grove et al. 2008) or landscape ecology (Forman 1995; Wu
and Hobbs 2002). Again, both of these reflect the holistic integration of natural, social,
and systems sciences. However, neither urban nor landscape ecology appear to address in
any direct manner the hardscape (infrastructure, e.g., buildings, transportation networks,
power distribution networks, communication networks) of urban habitat, the buildings
and building systems (and accompanying infrastructure) that populate urban ecology,
provide sheltered environments for the resident society, and have profound impact on
natural systems. They seem to be left to the realm of engineering resilience.

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The concept of resilience has accompanied the branching of human ecology into its
various disciplines, although it’s meaning is reinterpreted in the new context of each
discipline. Adger (2000) expresses the view that the concept of resilience cannot be
simply shared between scientific disciplines (referring, in this case, to ecological and
social sciences) in the absence of critical analysis, and in fact this is true of all the
disciplines where resilience has been developed as a meaningful concept. If the concept
of ecological resilience is to be considered as relevant to urban habitat, it must be
critically assessed and interpreted within that context. If such linkages exist between
ecology and urban habitat, then might they extend to buildings, and if to buildings then
their major systems. Given the interconnectedness of human and natural systems
embraced by virtually all of the scientific disciplines discussed here, it would seem
irrational to exclude buildings and their systems from this web. In this case, the
consideration is how might buildings impact the “ecological” resilience of urban habitat.
Pursuing this line of inquiry—the relevance of ecological resilience to the hardscape of
urban ecology—yields considerations different from those typical of engineering
resilience assessment. Not to say that the considerations of engineering resilience are not
relevant and important—they certainly are. But the critical assessment of ecological
resilience as potentially manifest in urban habitat provides a different perspective on
resilience, and reveals some different considerations. Adaptability, for example, is an
integral concept of ecological resilience, but is not a typical consideration of engineering
resilience.
The concept of ecological resilience is more evident at the scale of urban habitat, where
more complex, nonlinear patterns and self-organizing behaviors occur at the interface of
social, cultural, infrastructure, and architectural systems. Lovins and Lovins (1982, 177-
213) provide an excellent example of translating the insights of ecology and biology—
drawing directly from the work of Holling and others—to the built environment,
specifically to the power grid. In a section titled, “Toward a design science for
resilience,” they write:
Living systems evolve automatically if slowly towards resilience. Applying the
same principles to human affairs, however, requires the integration of biology
with engineering. Unfortunately, few engineers know much about biology. This
is partly because systems behave differently in biology than in engineering
textbooks. Engineers tend to be trained in a mechanistic, Newtonian tradition

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in which most systems are linear (responding smoothly in proportion to the
stimulus), reversible, and predictable. Living systems, on the other hand, are
full of delayed, nonlinear, threshold-before-crash behavior, with results as
irreversible as the scrambling of an egg. And yet living systems, in all their
vast complexity, have survived eons of rigorous environmental stress by virtue
of a carefully evolved capacity to bend, adapt, and bounce back even more
resilient than before. More precisely, those living systems, and only those,
which are observable today can be inferred, from their very survival, to be
masterpieces of resilience. The brittle systems became extinct. One might
therefore expect that such challenging areas of engineering as rivil
aeronautics, naval architecture, military hardware, nuclear reactor design,
and telecommunications would draw heavily on the insights that biological
resilience has to offer (Lovins and Lovins 1982, 190).
They go on to note, however, that with the exception of a very few engineers, such is not
the case. A similar viewpoint is expressed more recently in a Harvard Business Review
article discussing resilience and the continuing struggle with the failure of highly
complex systems (Zolli, 2012). The article makes the case for "taming" system
complexity, emphasizing the need for coupling this with cultural change that encourages
enhanced "cognitive diversity" as a means for people to "think more broadly and
diversely about the systems they inhabit," suggesting what some researchers refer to as
resilience thinking (Walker and Salt 2006; Folke, Carpenter, et al. 2010). Folke and
Carpenter focus on three aspects of social-ecological systems (SES): persistence,
adaptability, and transformability. Drawing from Holling, they characterize resilience as
" ... the tendency of a SES subject to change to remain within a stability domain."
Adaptability is the responsive change to internal or external drivers, a process of
development "within the current stability domain, along the current trajectory."
Transformation, in comparison, involves the creation of entirely new stability domains
and development trajectories in a deliberate process of "novelty and innovation,"
necessitating the attributes of resilience thinking. The shocks and stresses produced by
disaster events become to these authors "windows of opportunity" to drive social-
ecological transformation through regime change to a new stability landscape. They note
a relationship between scales:

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Transformations do not take place in a vacuum, but draw on resilience from
multiple scales…Transformational change at smaller scales enables resilience
at larger scales, while the capacity to transform at smaller scales draws on
resilience at other scales.
This interplay between scales is key to support the contention that considerations of
resilience are relevant to the building skin, and that responding to these considerations
with novel design solutions and delivery practices can enhance resilience not only at the
building system scale, but also at the progressive scales of building and urban habitat.
Both physical and temporal scales play a part in the findings of this research. The 1st
principle of resilient design developed by the Resilient Design Institute (2012-2013)
states this concisely:
Resilience transcends scales. Strategies to address resilience apply at scales of
individual buildings, communities, and larger regional and ecosystem scales;
they also apply at different time scales—from immediate to long-term.
The works of Folke and Zolli cited above reflect a convergence of science and business
in a deeper understanding of the concept of resilience. Industry has long been deeply
focused on shocks and disruptions through the practice of risk management, and working
from this foundation has also, like Folke and his colleagues, recognized opportunity in
the implementation of resilience that lie well beyond mere survival and recovery. In a
report prepared with the University of Oxford, PricewaterhouseCoopers (PwC 2012), one
of the leading international risk management consultants develops a business related
resilience theme that sounds remarkably like the resilience concepts emerging from the
social and ecological sciences. Referencing the concept of “bounce-back,” the report
notes that the term:
…demonstrates a shift in mindset from the old view of risk management that
implied removing uncertainty. Resilience accepts shocks will occur and the
organi[z]ation’s power of response is as important as its power of control.
(PwC 2012, 2)
But like the resilience concepts developed by these other sciences, the report also
embraces the notion that there is more to resilience than bounce-back:

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…bouncing back implies returning to the same position, whereas an
organi[z]ation seeking to be resilient over the long term requires something
else: the agility to create and seize opportunities, and to transform itself in
response to shifts in its environment.
Lovins and Lovins (1982, 181) have something quite similar to say, differentiating
between passive and active resilience:
…“passive resilience” describes the mere ability to bounce without breaking;
active resilience connotes the further adaptive quality of learning and profiting
from stress by using it as a source of information to increase “bounciness” still
further.
The PwC report goes as far as adopting the concepts of survival (persistence),
adaptability, and transformability:
Resilience not only helps to extend the focus beyond resistance to shocks to
include responses, but it also supports longer-term thinking about new risks
and opportunities. Some forms of risk management encourage us to focus on
the here and now. In contrast, resilience extends that frame of reference in
three perspectives…
• First, short-term survival: responding quickly and robustly to shocks.
• Second, adaptation: enhanced awareness of changes in the external
environment and the need for intelligent response.
• Third, transformation: moving into new markets and creating entirely new
experiences for customers.
The report goes on to discuss buffers and adaptive capacity; the complex and counter-
intuitive relationship between efficiency, redundancy, and resilience; and others,
interpreting these core concepts into the context and language of business management
and an evolving practice of risk management. And yet the urban resilience dialogue
remains largely confined to resistance and survival thinking.
As both Holling and Lovins point out, the resilience dialogue in the building arts is about
engineering resilience: shock, recovery, preparedness, and risk assessment; an effort to

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bring predictability and increased efficiency of response to what may be an ultimately
unpredictable evolution. Central to the concept of ecological resilience are the
characteristics of change, unpredictability, and uncertainty, a different discussion that
adds considerable depth and brings important new considerations to the dialogue. The
linear assessment characteristic of engineering resilience avoids the complexity that
might reveal deeper causal patterns affecting the stability of urban habitat. The urban
resilience movement, for example, is in part an engineering response to the escalating
magnitude and frequency of storms. This is, however, a response to the symptoms of
climate change driven by the excessive energy consumption and accompanying carbon
emissions produced by the building sector. The response ignores the larger causal forces
at play. Ecological resilience in comparison is measured not by recovery time, but by the
ability to learn, to adapt, to transform, which, when applied to the built environment, may
bring a new set of considerations to the forefront.
Furthermore, there is a relationship between engineering resilience and ecological
resilience, whereby narrowly focused overemphasis on engineering resilience can
undermine ecological resilience resulting in the “brittleness” that Lovins references,
raising the potential for catastrophic disruption, as systems that have been stripped of
their ability to adapt and transform encounter unanticipated conditions. The engineering
pursuit of efficiency, often at the expense of redundancy, can be causal in this respect.
Again, the PwC (2012, 3) report recognizes this as a business threat:
Like an athlete who pushes fitness to the point where the immune system is
damaged at the risk of regular infection, many organi[z]ations have pursued
efficiency to the point where it could undermine resilience.
The overarching question then, is does this concept of ecological resilience have
relevance to the built environment:
1. Is urban resilience ultimately as much about uncertainty as it is predictability,
with the formulaic linearity of the predominant engineering resilience eroding at
its foundation by the nonlinear complexities characteristic of organic systems?
2. Is it possible for buildings, building types, building designs, building systems,
materials, or components to compromise urban resilience to the point that
resulting stresses trigger an unanticipated domain change, a fundamental change
in character?

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3. Is it conceivable that some aspect of building performance, in combination with
interconnected influences and across scales, could result in residual stresses that
ultimately become the perturbation that flips the urban domain to an unforeseen
state?
4. Could tall buildings, or all-glass facades, or unventilated buildings, or poor energy
performance, or combinations of these aspects interacting with other social or
natural system factors yield unanticipated and unpredictable outcomes producing
a regime shift?
5. Does the concept of active resilience signify with respect to buildings and
building systems?
6. Can buildings and their major systems “learn” in a manner that embraces
adaptation and transformation, thereby benefiting from rather than just recovering
from disruptions?
7. Or is it the designers and builders that have to do the learning, implementing built
infrastructure that readily accommodates adaptation and transformation in
response to a wide range of disruptive emerging conditions?
This is a deeper aspect of resilience and the built environment that should be considered,
and critically evaluated for integration into the current resilience dialogue and practices.
The foregoing can now serve as a reference to aid in the development of a concept of
urban resilience that can be translated through the scales of urban habitat, buildings, and
major building systems, an exploration aimed ultimately at defining specific resilience
considerations for the building skin.
6.5 Resilience by Design
Popular definitions of urban resilience often pull up short at the ability to rebound in the
wake of a disaster related event. This misses the nuance of the concept and its ability to
inform building design and delivery processes. The manner in which design process
embraces considerations of resilience is of particular interest. Resilient design addresses
building and building system vulnerabilities in the face of shocks and stresses during and
following an emerging spectrum of natural and manmade disasters. Unrelieved long-term
stresses may in fact yield the disaster, but urban resilience initiatives remain
predominantly focused on the perturbations resulting from the more dramatic shocks
produced by natural disasters such as hurricanes and manmade disasters such as violent

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acts of terrorism. Anticipating the magnitude and frequency of such disasters given the
vagaries of emerging climate change and the potential for future social unrest from a
variety of causes is a part of the resilience challenge. Climate change considerations
include droughts, floods, storms, wildfires, and temperature extremes. Other natural
threats include seismic events. Anthropogenic disasters include the escalating potential
for social unrest and acts of terrorism aimed at buildings and building infrastructure,
including the extensive networks responsible for providing water, energy, and
information to buildings.
The threat these risks pose to the built environment is driving comprehensive assessment
and a growing response at national, regional, and local levels. The recurrence of powerful
storms and the resulting cost in money and lives has brought a sense of urgency to this
response. Many major cities have developed and adopted resilience plans—New York
City (plaNYC, A Stronger More Resilient New York); Chicago and Los Angeles(100
Resilient Cities); Seattle (The PNW Resilience Challenge, and many others—and
organizations have sprung up to facilitate these efforts; 100 Resilient Cities (2015), an
effort pioneered by the Rockefeller Foundation, and the Resilient Design Institute (2012-
2013) led by BuildingGreen founder Alex Wilson. Much of the focus is on urban
infrastructure including buildings. The building envelope occasionally enters into the
conversation, but seldom as a specific focus of resilience considerations.
The problem, as noted above, is that the focus of these plans and efforts orbits too tightly
around the short-term impact of shocks and misses the subtleties of the long-term stresses
that can slowly and insidiously strip resilience in a manner that may not be recognized
until unanticipated conditions emerge to potentially devastating effect. For example, the
focus on superstorms and the flooding they produce drives resilience initiatives that
concentrate on linear responses, like raising buildings or their primary services and
habitats above projected maximum storm surge levels. Meanwhile, conditions that may
jeopardize other primary infrastructure systems are ignored; the electrical power grid and
transportation systems are two good examples. Components of these systems were not
designed with adequate service lives, were not maintained, or both, resulting in what
Lovins referred to earlier as brittle systems. The aging curtainwall facades on the
skyscraper buildings that emerged in the mid twentieth century are another case in
point—they are well passed their intended service life, with many in desperate need of
retrofit, yet the need for future retrofit was not anticipated in the design of these façade

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systems. In consequence, the only course of action is often the removal and replacement
of the entire façade system, a practice so costly and disruptive to ongoing building
operations that few buildings have undergone facade retrofit. Yet this shortsighted
practice continues even today, and curtainwall systems are designed and installed with no
consideration of future retrofit needs, despite the fact that retrofits will be required before
future energy and carbon reduction goals in the building sector can be met. Tomorrow’s
problems are being built today, but are not recognized for their embedded impacts certain
to compromise future urban resilience. As these primary elements of urban infrastructure
continue to age into the future, failures will increase and performance will suffer,
bringing increasing stress upon urban society, and potentially converging in a manner to
present insurmountable economic challenges to communities already stressed by
escalating conditions of climate and social change.
6.5.1 Resilience Thinking
The notion of resilience thinking (Walker and Salt 2006; Folke, Carpenter, et al. 2010)
was introduced earlier. The importance of resilience thinking as integral to design
practices intended to yield resilience is the emphasis here. The growing awareness of
urban resilience is informing design.
The shift in focus from sustainability to resilience is bringing renewed consideration in
the building arts of such fundamental conceptual pairings as redundancy–efficiency, and
simplicity–complexity. In his book, Designing to Avoid Disaster: The Nature of Fracture
Critical Design, Thomas Fisher (2013, loc 306-393) challenges the status quo mentality
regarding redundancy and efficiency, pointing out that the pursuit of efficiency
characterized by routine engineering practices is stripping important redundancy from
infrastructure products and systems. Fisher uses the I-35W bridge collapse (Minnesota,
2007) as an example of the catastrophic effect that can result from an overly efficient,
highly interconnected design, lacking redundancy. The failure of a simple gusset plate
resulted in catastrophic failure; a cascade effect that progressed through the hierarchy of
interconnected structural components until the bridge itself collapsed. The collapse was a
reordering of the bridge system resulting from the preconditions of over efficiency,
interconnectivity, and a lack of redundancy that reduced system resilience, leaving the
bridge vulnerable to a gradual increase in stress in only a small part of the system.

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Fisher uses the engineer’s reference of redundancy as a strategy to improve structural
reliability through replication, as when providing multiple load paths in a structural
design, but he also links this usage with ecological science, and specifically to the work
of Lance Gunderson and C.S. Holling (2002) in the book Panarchy: Understanding
Transformations in Human and Natural Systems. In the ecological systems of panarchy,
redundancy relates to the biological diversity of various functional attributes exhibited
within and between species, and represents behavior characteristic of the adaptive cycles
of both natural and manmade systems. Over-efficiency that reduces redundancy may strip
resilience, resulting in brittle systems producing cycles of system collapse and
reorganization (Figure 6.1). Lynch (1958, 23) notes a “continuous conflict between future
adaptability and present efficiency.” This notion is often overlooked by engineering
practice that, while acknowledging redundancy as a valid property, recognizes that each
unit weight of material adds to the cost, and pursues efficiency as a strategy to reduce
cost. This problem is exacerbated with complex systems, where properties of redundancy
may be obscure and not revealed until unanticipated conditions trigger unforeseen
disruptions.

Figure 6.1: Over efficiency can reduce redundancy and the ability of a
system to adapt to stresses, causing collapse and return to a state of
less efficiency but greater resilience (adapted from Fisher 2013, loc
348).
The primary thrust of efforts to improve performance in the built environment has been
the realization of carbon reductions achieved through greater energy efficiency. Energy

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consumed during the operational phase of a building is the most considered case in point.
Progress has been made in making buildings more energy efficient. But high-
performance buildings and building systems that achieve efficiency gains through added
complexity may be more expensive, and considerably more challenging to operate,
maintain, and repair (and, ultimately, more vulnerable, and therefore less resilient).
Simplicity is an underrated attribute of sustainability and resilience; there is a question of
how much complexity can be sustainably supported. Too often, high performance in
buildings and building systems is achieved through additional layers of complexity.
Kinetic systems are an example. Shading louvers on the building exterior can respond
dynamically to changing conditions of sunlight on the building façade. But kinetic
systems involve motors, controllers, sensors, programming, and maintenance, bringing an
order-of-magnitude of additional complexity over passive systems, and often times an
order-of-magnitude higher cost, as well. Do such systems add or detract from resilience?
The answer can only be discovered through careful and comprehensive life-cycle
analysis, but resilience thinking reveals that it is incumbent on designers to balance
simplicity and performance, combining efficiency with necessary redundancy to achieve
the simplest solution to a contextual problem. Efficiency accomplished through
increasing complexity may easily reduce resilience.
6.5.2 Resilience at Scale
The pursuit of efficiency can have other unintended consequences. The press for energy
efficiency improvements in buildings led to the widespread adoption of insulated glazing
starting in the mid 1970s, and to the development and popularity of today’s high-
performance glazings utilizing low-e, spectrally selective coatings, and gas fills for
improved insulative and solar control properties. While these high-performance glazings
have contributed to the improved energy performance of highly glazed buildings, it has
negatively impacted the important considerations of durability and recyclability,
collapsing the service life of raw float glass from a measure of centuries to decades, and
rendering architectural glass impractical for recycling. These consequences may or may
not affect resilience at the building scale, but the broader context provided by ecological
science reveals the potential for impacts to resilience at local and regional scales as
landfills overflow and unplanned renovation costs burden already stressed economies.
The point is that research into the system dynamics of ecological and socio-ecological
systems has revealed that change often propagates unpredictably across interlinked scales

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(Holling and Gunderson 2002, loc 612; Walker et. al. 2004, 2). The contention here is
that human habitats are ecosystems, and that the discoveries and theories of ecological
science can inform the process involved in the implementation and evolution of the built
environment. Unpredictable outcomes can be anticipated as actions and actors (systems,
products, practices) move, for example, from the building system scale to the building
itself, then to local, regional, or national scales. A question is if buildings or building
systems can be considered resilient if they do not contribute to resilience at these other
linked and overlapping scales. This argument begins to add relevance and form to the
hypothesis that resilience at the façade scale can, and perhaps must, translate
meaningfully to resilience at the larger scales of building and urban habitat.
Holling (1993; Holling and Gunderson 2002, loc 637, 1131) notes a distinction between
the popular use of the term resilience as the ability to bounce back in the aftermath of a
disaster related impact, and their panarchy definition of the ability of a biological or
social system “to withstand disturbance and still continue to function,” with a resilience
metric being the magnitude of impact the system is capable of withstanding without
significant functional compromise. This subtlety is useful when considering the resilience
of buildings. First, it’s not just a matter of what happens in the aftermath; performance
during the disturbance is equally important. We want the building structure to bend and
not break during a seismic event, for example. There will be little “bounce back” in the
aftermath if the building structure fails. This has been discussed as engineering resilience.
Second is the degree to which critical functions are maintained without disruption both
during and after an event. The resilience of a system is somewhat comparable to the
evaluation of durability, in that the weakest link determines the service life of a system.
Similarly, the weakest link in a building or building system can determine its resilience.
Consider what happens when the electricity supply to a building is disrupted. In many tall
buildings, owing to a lack of redundancy that might be provided by backup generation
and storage systems, the lights go out, and air conditioning, ventilation, vertical transport,
water delivery, communication, and waste disposal systems cease to function.
Holling’s description of engineering resilience dominates the urban resilience movement,
with considerations manifesting in two primary areas: life-safety and property damage.
The building community is tasked with protecting people from injury both during and in
the aftermath of a disruption. This becomes the overarching consideration of resilience

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across scales within the built environment, from building systems to community
infrastructure. The mandate is not merely about protecting populations; it is about
protecting individuals. The topmost measure of disaster resilience is loss of life: how
great a disturbance can be withstood without loss of life.
Yet the damage resulting from shocks, while a lesser order concern than life-safety, is an
important measure of resilience. Not only must buildings and infrastructure function at
some baseline level during disruption and bounce back quickly in the aftermath, it is
important for them to do so with minimal damage. The stresses wrought by extensive
damage can compromise resilience at the community scale, prolonging disruption and
resulting in long-term economic and social impacts even at the regional and national
scales. Parker and Carlson (2010) have examined predictive methods for estimating the
potential for damage from classes of seismic activity to a given building project, and
make the case that designing to mitigate the life cycle cost of this impact is an important
sustainability consideration. The analysis here reveals that this could properly be
regarded as an attribute of resilience. Property owners and their insurance companies
have refined risk assessment practices developed over many years, based largely on a
statistical evaluation of historical data, that aid in evaluating loss potential from property
damage due to disaster events. As awareness of an uncertain future expands, however,
there is a growing recognition by the industry that these practices may be inadequate, and
the concepts of ecological resilience are being adopted to establish a context for more
robust practices of risk assessment. As a Pricewaterhouse report comments:
As predictability wanes in a turbulent world, so the need for buffers and
adaptive capacity increases.
So, what does this all mean when applied to a real building project? What are baseline
characteristics of a resilient building? Can design practice modifications achieve these
characteristics?
6.5.3 Design Objectives
In summary, the aim of resilient design is to develop buildings, building systems (like the
façade system), and key infrastructure that:
§ bend without breaking,

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§ anticipate and accommodate future loads resulting from extreme natural and
anthropogenic events,
§ maintain conditions for human safety, health, and comfort during and following
system shocks, and throughout prolonged system stresses,
§ recover rapidly from system shocks,
§ mitigate damage in a manner to facilitate speedy recovery to the pre impact state
of functionality while minimizing the cost to do so,
§ facilitate adaptive strategies able to accommodate the certainty of the unexpected,
§ and that supply basic needs—air quality, comfort, lighting, water, food, and
sanitation—with a priority given to simple, passive, and redundant solutions.
How well do conventional building practices address these objectives? Most building
design relies on prescriptive building codes. But do these codes address these important
objectives for resilience? Do building codes anticipate the looming impacts of climate
change? Are building owners and the public exposed to unaccounted risk by simply
following model building codes?
The Insurance Institute for Business & Home Safety (IBHS) is a member organization of
insurers and reinsurers with a mission of objective, scientific research on property loss
resulting from natural and man-made disasters. Through the National Institute of
Building Sciences’ Whole Building Design Guide, the IBHS (2013) recommends the use
of code-plus programs over model building codes—like the International Building Code
(IBC)—which are minimum life safety standards and may not provide adequate property
protection. An example would be the voluntary adoption of Florida Building Code
standards for wind pressures and missile-impact resistance for façade systems in areas
along the eastern seaboard that are not currently subject to these more demanding
standards, including a demanding regulated product approval process (Miami-Dade
County 2015). Condon (2012, 326) recommends the adoption of code-plus standards for
glazing products used in essential facilities in Category-3 hurricane zones. Adopting a
code-plus approach early in the design process accommodates the development of
specific building resilience goals. This approach can be developed into a resilience plan
that becomes a part of the basis-of-design (BOD) between the design team and the owner.
As with the axiom, “What gets measured gets done,” the implementation of such a
strategy is likely to amplify the potential for realizing enhanced building resilience.

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6.6 Façade Links to Resilience
A stated goal of this research is to establish a relationship between resilience and the
building skin, and to investigate how this relationship may extend to the progressive
scales of building and urban habitat. On their website, the IBHS (2013a) lists earthquake,
flood, freezing weather, hail, high winds, hurricane, lightning, tornado, and wildfire as
categories of property risk. As the arbiter between the building interior and ambient
climate conditions, the building façade is easily recognized as integral to this discussion
of risk, as the following considerations illustrate:
§ Seismic: Facade systems must accommodate extreme building movements
resulting from seismic events in a manner that prevents glass breakage and falling
components, and that minimizes extensive damage and consequent economic
impact.
§ Flood: Facade systems at the ground level may be subject to storm surge and
flood, presenting risk to the building, its occupants, and the public.
§ Extreme temperatures: Occupants can be protected from potentially life-
threatening temperatures by the mitigating influence of a well-insulated façade,
but unventilated facades can quickly pose life threatening conditions when
cooling systems fail.
§ Extreme winds associated with tropical storms, hurricanes, and tornados are the
most widely recognized threat to the building skin, with damage resulting from
high wind pressures and the impact of airborne debris.
§ Building fires in dense urban environments provide the corollary to the risk posed
by wildfire, as was seen in the DaVinci apartment tower blaze in Los Angeles in
2014. The fire occurred while the building was under construction, and shut down
two major freeways through downtown LA. The intense heat caused extensive
damage to surrounding buildings, breaking windows and warping wall panels, and
badly disrupting operations; two buildings were not to be occupied until follow up
inspections could determine the extent of the damage and execute necessary
repairs. Damage to freeways and buildings was estimated at $25-30 million.
These considerations evidence a strong and relevant relationship between resilience and
the building skin. Further consideration of the impacts resulting from these broad
categories of risk yields additional performance variables for assessment. Any of the
above risks can easily disrupt the electrical grid, and as noted above, many measures of
resilience are most easily recognized in consideration of “what happens when the lights

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go out;” e.g., the supply of electricity to the building is disrupted. In addition, it’s not just
the risks presented by natural disasters that can compromise the electrical grid, but acts of
terrorism can directly target key infrastructure like electricity and water supply that
buildings rely upon. Aging and stressed infrastructure can produce similar results,
spreading these stresses throughout the build environment.
Therefore, acts of terrorism and civil disorder, and the potential impacts of aging and
stressed infrastructure can be added to the risks detailed above. How might these issues
impact the façade system? Blast, ballistic, and forced-entry resistant systems can be
employed in response to the former, and as the latter—along with all of the other
identified risks—hold the potential for electrical power disruption, design strategies
ranging from operable windows to prevent extreme overheating if cooling systems fail, to
façade-integrated power generation independent of the electrical grid may be adopted.
Such ideas would necessarily need to be evaluated in the context of the many variables
that comprise a specific building project. The objective here is not to test the relevance or
viability of such individual strategies, but to reveal a relationship between resilience and
the building skin, and to demonstrate how resilience thinking can provide a fresh
prospective on façade system design with the potential to enhance resilience.
6.7 The Subtleties of Resilience
The risks posed by extreme temperature, wind, flood, seismic events, and their resulting
impacts, may be relatively obvious. There are more subtle issues, however, that are
revealed through resilience thinking.
6.7.1 Delivery Processes and Supply Chains
Building delivery processes and supply chain strategies are an example. Robust conduits
of key materials, products, and services are vital in the wake of disasters resulting in
damage to buildings and infrastructure. High levels of customization and price pressure
during the design process often result in convoluted supply chains that circumnavigate
the planet as contactors pursue unique capabilities and competitive pricing. Such
materials may be unavailable if needed in the future, or may require problematic delivery
times before building serviceability can be restored. The USGBC’s LEED building rating

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program awards points for material proximity to the building site, but resilient supply
chains cannot afford to be too exclusive and too local, as local supply sources may be
compromised by the disaster (this point illustrates the related but different perspectives of
resilience and sustainability). Also, the availability of multiple vendor sources provides
redundancy to the supply chain, enhancing resilience.
6.7.2 Durability
Furthermore, as the Resilient Design Institute (2012-2013) points out, durability is a
resilience issue: “Strategies that increase durability enhance resilience.” Remarkably,
building facades—and buildings themselves, for that matter—are very rarely designed for
a defined service life. Building lifespans are commonly thought of in the 30 to 50-year
time range, with 100-year buildings being the rare stretch (Section 4.3.11). Dr. Antony
Wood, executive director of the Council for Tall buildings and Urban Habitat, comments
(Miller 2015):
It’s patently ridiculous that we talk about buildings have[ing] a design life of only 50 to
100 years,” he says. “We should be designing for the ages, as there is very little practical
experience in dismantling tall buildings—not to mention [it being] destructive to the
environment and a waste of embodied energy—and modifications can be prohibitively
expensive.
Façade systems suffer from the same limited design thinking, and as a consequence,
aging facades in the existing building stock currently represent a looming need for retrofit
on a massive scale. As pointed out earlier, significant performance enhancements that
could result from façade upgrades are delayed because of the substantial cost—and costly
disruption to ongoing building operations—accompanying these retrofits. Much of the
reason for the challenges presented by the retrofit of these façade systems is the failure to
anticipate and accommodate the imminent need for future retrofit in the design of these
systems. It is concerning to note that current façade design practices still do not anticipate
the need for future retrofit despite the obvious inevitability. If commonly embraced goals
of net-zero in the commercial building stock from 2030 to 2050 are to be realized, the
buildings being constructed today will require façade retrofit to meet this goal, as the
required technology is simply not currently available (crossref chapter), yet no provision
is made to accommodate this future need. The result brings brittleness to the façade
system, stripping resilience from the building and urban habitat. Resilience thinking

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would anticipate and address this shortcoming through the development of adaptive
capacity in the façade system.
6.7.3 Adaptability
We have to start designing and building for a future we cannot fully anticipate.
Durability is important, but adaptability is perhaps more so. Facades are the
first line of defense in this cause. – Dr. Antony Wood (Miller 2015)
While struggling to deal with the challenges presented by an aging building stock, the
industry may well be continuing a practice of building construction that will only further
burden future generations. As discussed earlier, resilience concerns both impacts and
stresses. Economic considerations are currently delaying the widespread renovation of
aging and under-performing building facades. Continuing to retrofit and build new
facades using current design and delivery processes could bring further and more
debilitating future economic stress, and even stall the progress to a net-zero built
environment. There is no way to know that the money to fund such a massive conversion
of the building stock will be available. A solution is to design more robust and durable
facades today, façade systems that are net-zero “ready,” that anticipate and accommodate
the need for future adoption of emergent technology. Therefore, adaptability is yet
another relevant resilience consideration; the more durable the façade system becomes
the more important the ability to readily adapt as required to adopt future technology, as
well as the system flexibility that accommodated adaptation to changing conditions of use
(Section 4.3.7).
Acceleration of the linked phenomena of social and technological change brings high
uncertainty as to how buildings might be used even twenty to thirty years from now,
much less a century from now. Yet buildings represent such a massive commitment of
resources that service life targets of hundreds of years, or longer, seem increasingly
appropriate (Brand 1994, 194). Durability and adaptability, therefore, are identified as
important considerations of resilience, along with processes such as maintenance that can
effectively extend service life (Brand 1994, 110-132; Kesik 2002; Blom et al. 2010,
2537).
Adaptation is used in the literature of climate change as approximately “adjustment in
natural or human systems in response to actual or expected climate stimuli or their effect,

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which moderates harm and exploits beneficial opportunities” (McCarthy et al. 2001,
982). Designing buildings and their major systems to facilitate future adaptation is a
strategy to “moderate harm” and “exploit beneficial opportunities” as the uncertainties of
tomorrow are revealed. Lynch (1958, 16-24), however, notes the complexity and
challenge of attempts to increase future adaptability, including
1. additional resource requirements,
2. increased first cost and ongoing operating cost,
3. a continuous tension between future adaptability and present efficiency.
The emphasis must be on strategies that cost little or nothing in first or running costs and
that improve both efficiency and adaptability.
6.7.4 A Methodology for Evaluating Façade System Resilience
A methodology for addressing façade resilience begins to emerge, a methodology that
diagrams the relationship between resilience and the building skin (Figure 6.2).
Categories of considerations and performance variables can be drawn from the risks
identified above, and characterized as resilience factors, the term factor meaning in this
instance a circumstance or influence that contributes to an outcome, e.g., storm surge and
flood represents an influence that effects resilience. Strategies and tools can then be
evaluated in terms of their potential for enhancing factor resilience. Finally, metrics and
processes can be adopted or developed linking factor and strategies as relevant and
appropriate. A metric, as used here, is intended as a standard of measure that can be used
to assess a specific performance attribute of resilience. Measures can address efficiency,
performance, progress, or other qualities of performance, or of a practice, process, plan,
or product. Metrics can be challenging to develop, but useful in evaluating status.

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Figure 6.2: Organizational strategy for categorizing attributes, measures, and strategies of façade
resilience.
As an example, consider the performance attribute of design wind load as a resilience
consideration. The common metric is wind pressure, either in SI or Imperial units. It
could prove useful with this methodology to include both current practice, which in the
case would be code minimums, and aspirational targets, as with the adoption of code-plus
higher order wind loads. Strategies to address wind load performance as a resilience
consideration could include
§ the adoption of South Florida building code requirements for wind load
determination and missile impact testing requirements in coastal and near coastal
areas even when it is not required.
§ the use of forecast data (rather than code requirements based on historical data) in
determining design wind loads,
§ the use of wind tunnel testing as a more accurate measure of wind loads on a
particular building configuration as compared with prescriptive code techniques,

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§ the specification of laminated or double-laminated glass fabrication,
§ system detailing to enhance the retention of glass and other panel materials under
extreme wind forces,
and so on. The initial exercise in executing this methodology is to develop a concise set
of resilience factors derived from the various risks discussed above, and the potential
impacts and stresses resulting from these risks. These would include storm and flood,
extremes of temperature and wind, fire, and acts of terrorism, as a start.
6.8 Principles of Façade Resilience
Resilience is a complex issue at any scale, including the scale of major building systems
such as the façade. The following principles have been developed to guide the pursuit of
appropriate practices—considerations, metrics, and ultimately, tools and strategies—for
achieving resilient building skins. Some of the principles are more generalized to
considerations of resilience, some more specific to the façade system. The façade specific
principles could potentially be extrapolated to a more general context; e.g., highly custom
facades are less resilient, but customization as a general principle may strip resilience.
The 10 principles are indicated in Table 6.1.
Table 6.1: The following principles of façade resilience are a product of this research derived from
workshops, surveys, and literature review as described in Section 2.5.4, and partially derived from
the work of the Resilient Design Institute (2012-2013a).
10 Principles of Building Façade Resilience (Summary)
1. Resilient facades bend—absorb impacts—without breaking.
2. Resilience is contextual, and must be developed case-by-case.
3. Resilience and sustainability are linked concepts.
4. Resilient façade designs anticipate future uncertainty.
5. Safety, health, and comfort are resilience considerations.
6. Facades are contributory to resilience at the scale of building system, building, and urban
habitat.
7. Facades uniquely affect resilience both performatively and aesthetically.
8. Minimizing façade system complexity and preserving redundancy enhances resilience.
9. Highly customized façade systems are less resilient.
10. Durable and adaptable façade systems enhance resilience.

1. Resilient facades bend—absorb impacts—without breaking. Resilient façade
systems mitigate the risk to health and safety of building occupants and public

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areas surrounding the building during and after a disaster, over the lifecycle of the
building. They also mitigate the risk of property damage to the system, building,
and surrounding habitat and buildings in the same conditions. It is important for
façades to resist breach and mitigate risk of falling materials from extreme wind
pressures and impacts from airborne debris.
2. Resilience is contextual, and must be developed case-by-case. Façade
resilience considerations encompass the unique conditions of building use, site,
configuration, microclimate, functional requirements, façade orientation and
exposure, in a highly contextual future-looking risk assessment of short-term
shocks and long-term stresses.
3. Resilience and sustainability are linked concepts. Resilience cannot be
achieved at the expense of sustainability. A resilient façade must contribute to
building material and energy efficiency and other sustainability considerations,
thereby supporting sustainable buildings and communities. Sustainable building
practices encompass considerations of resilience. Bind resilience goals and
supporting strategies to considerations of performance and sustainability.
4. Resilient façade designs anticipate future uncertainty. Both climate and social
change are accelerating, with effects challenging to predict. The only certainty is
that of unpredictable outcomes. Let the ambiguity of an uncertain future drive
design decisions.
5. Safety, health, and comfort are resilience considerations. The motive for a
more resilient built environment is in support of more resilient communities, and
ultimately, a more resilient human population. People, on average, spend about
90% of their time indoors (EPA 2011). Human safety, health, and comfort, then,
are largely shaped by the interior environment, which in turn is largely shaped by
the building skin as arbiter between conditions inside and outside. Occupant
safety is reliant upon the integrity of the façade system throughout the range of
possible exterior conditions. In addition, the provision of view, daylight, and
access to fresh air are contributory to human health and comfort, thereby directly
contributing to a more resilient human population.
6. Facades are contributory to resilience at the scale of building system,
building, and urban habitat. A reductionist approach to resilience may produce
a façade system that is more resilient, for example, in the face of shocks resulting
from a major storm event, but a holistic approach can produce a façade that is not
only more resilient as a building system, but that also enhances building and
community resilience in ways that surpass the resilience of the façade system
itself. A façade system that harvests rainwater or solar energy, for example, is not

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necessarily more resilient than one that does not, yet holds the potential to
contribute to the resilience of the building and surrounding community.
7. Facades uniquely affect resilience both performatively and aesthetically. The
building skin uniquely manifests pronounced effects to both appearance and
performance across the scales referenced in principle 6. While performance issues
tend to dominate the dialogue, aesthetics may be the ultimate determinate of a
building’s resilience; buildings that are recognized and loved for their appearance
are more valued, and consequently better cared for. Beauty enhances resilience.
8. Minimizing façade system complexity and preserving redundancy enhances
resilience. Performance improvements attained through added complexity and
highly optimized efficiency strip redundancy and produce brittle systems.
Performance enhancements must be evaluated in the context of preserving system
redundancy and minimizing system complexity. For example, kinetic systems
incorporated in the building skin must be carefully evaluated in this context, and
passive strategies should be pursued as a priority. There are other less obvious
considerations. High-performance glass solutions that rely on hermetically sealed
gas-filled cavities my compromise durability, and thereby resilience. Single seals
as the sole line of defense against air and water infiltration that, once installed, are
not accessible for inspection or maintenance, may easily compromise energy
performance, comfort, and durability, and ultimately, resilience.
9. Highly customized façade systems are less resilient. High levels of system
customization tend to strip resilience by increasing complexity and limiting
supply chain options for future system maintenance, renovation, adaptation, and
replacement. To the extent that highly custom façade solutions are used, they
should be developed with specific goals to enhance resilience. The use of a
standardized technology developed to accommodate customized applications
utilizing a robust supply chain is a good strategy to varying contextual
requirements while maintaining resilience.
10. Durable and adaptable façade systems enhance resilience. Durability and
adaptability of typically left out of the resilience dialogue. The service life of
buildings and their major systems is rarely specified. Resilience is a lifecycle
forward-looking consideration that attempts to anticipate future uncertainty while
at the same time preparing for the certainty of surprise. Durability minimizes the
stress, economic and otherwise, that accompanies maintenance, renovation, and
replacement of buildings and their major systems (e.g., the façade system).
Adaptability of the service life of the system accommodates change, whether
changing conditions of climate, building function, or patterns of use resulting
from social evolution.

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6.9 A Framework for Building Façade Resilience
The 10 Principles of Façade Resilience (Section 6.8) establish the foundation for deeper
consideration of the building skin, with the goal of enhancing the resilience of this
integral building system—and thereby that of the building, neighboring habitat, and
community. The goal now is to establish a framework for the evaluation of façade
resilience. The framework is intended to accommodate the organization and facilitate the
identification of specific strategies—and supporting metrics—with the potential to
elevate resilience in the face of the shocks and stresses that have been discussed
throughout this research.
As introduced in section 6.7.4, the organizational strategy is to develop appropriate
considerations and performance variables as resilience factors: primary categories of
resilience considerations with respect to the building skin (Figure 6.3; Table 6.2).

Figure 6.3: The Resilience Strand is comprised of the primary
attributes and considerations of façade resilience.
These resilience factors are then considered for measures ranging from metrics to
processes that can be used to evaluate the factor quality. Where relevant, values

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representing current practices, such as building code minimum standards, can be
indicated as well as aspirational targets in support of enhanced resilience. The objective is
to develop specific strategies relevant to each of the resilience factors that hold the
potential for improving their respective resilience value. Figure 6-1 diagrams this
methodology.
Twelve resilience factors have been identified. Some have been drawn directly from the
various risks discussed in section 6.6, like storm and flood, extreme temperature, extreme
wind, and fire. Others have been derived from potential resilience strategies discussed
earlier, as with the use of a code+ approach in specifying façade system requirements.
Still others, like durability and adaptability, are drawn from the 10 Principles of
Resilience, which themselves track back to various aspects of the ideas generated from
surveys and workshops conducted as part of this research. Table 6.2 documents the 12
categories.

Table 6.2: Twelve factors have been identified as the primary attributes of façade resilience.
RESILIENCE FACTORS
1. design goals Goals are measurable. Measuring enhances probability of achievement.
2. design loads Key design loads can be tuned to resilience considerations.
3. electrical grid disruption What happens when the power goes off?
4. storm surge; flood The greatest threat to life and property during coastal super storms.
5. extreme temperature Extreme highs + lows stress building systems and urban infrastructure.
6. extreme wind The dominant resilience threat to the façade system.
7. fire Urban fires are the corollary of wildfires in natural ecosystems.
8. security Resilience considerations anticipate potential for escalating social strife.
9. durability Service life exposure can produce its own stress over time.
10. adaptability Durable systems must anticipate changing conditions of use over time.
11. recovery Not just absorbing shock, but time and cost to rebound to initial state.
12. health & comfort The wellbeing of a population is a resilience factor.

6.9.1 Resilience Factors
1. Design goals: Enhanced resilience is unlikely to be achieved in the absence of
clear, specific, and measurable goals. These goals should be part of the building
program, or basis of design (BOD), between the owner and the architect, and
established early in the design process. Ideally, this can take the shape of a formal

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resilience plan. The plan would consider the risk exposure of the building to the
various resilience factors identified in the table as a function of building
configuration, location, conditions of use, and other relevant contextual
considerations. Every building project presents a unique context in this regard.
2. Design loads: The engineering resilience of buildings and building systems is an
important issue. The code+ discussion earlier points to the benefit of adopting
specifications that exceed the requirements of model building codes. This is an
obvious consideration with respect to wind load criteria and the escalation of
storm intensity and frequency resulting for climate change.
3. Electrical grid disruption: The impact of power outage, especially long term,
can be both disruptive and life threatening. Strategies developed for this resilience
factor may not necessarily increase the resilience of the façade system itself, but
instead address how the façade may contribute to resilience at the larger scales of
building and community during extended grid disruptions.
4. Storm surge & flood: This is typically the source of the greatest disruption and
threat to life and property during coastal super storms. The effect on the façade is
limited to near ground level in all but extreme cases. Buildings constructed in
known flood zones should consider the use of knock-out walls that can be
repositioned and secured in advance of a storm, to prevent the transmission of
excessive loading into the building structure, and the threat posed by components
breaking free of the façade under flood loads. All glass that could be exposed to
flood waters and floating debris should be safety glass.
5. Extreme temperature: Climatic temperature extremes can stress building
systems and urban infrastructure, including stress to façade materials, causing
thermal stress fracturing in glass, for example. Indirect impacts include power
outages that can occur as a result of extreme high or low temperatures, which can
quickly result in potentially life threatening interior temperatures if ventilation
and HVAC systems fail (Urban Green, 2014).
6. Extreme wind: Tropical storms, hurricanes, tornadoes, and microbursts, all
involve high wind pressures and the potential for airborne debris, representing a
direct threat to the façade system. Glass is particularly vulnerable. Strategies need
to focus on preventing a breach to the building skin that can quickly amplify the
threat of further damage and injury. Current practices focus on the use of
laminated glass. (Minor 1994, 207)
7. Fire: Several of the resilience factors embodying risks other than fire, are
accompanied by the potential for fire as a second order effect. Extreme wind and
temperatures, seismic events, floods, militant acts, and grid disruptions are all

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potentially contributory to building fires. Exposure to fire can also result from
close proximity to neighboring buildings, as is common in the urban environment.
8. Security: Façade system security measures pertain largely to the lower floors in
most buildings, but some special purpose buildings may involve security
considerations over the entire building skin. Large commercial buildings in major
urban environments are increasingly incorporating some level of blast design
criteria at the ground floor, even in the absence of any code requirement to do so.
The specification of blast criteria is typical in government buildings.
9. Durability: Durability is a fundamental attribute of sustainability that has
important resilience implications. Durability effects resilience in two ways. First,
the premature deterioration of building systems amplifies the potential for damage
and injury resulting from the various risk factors. Second, the premature or
unanticipated deterioration of building systems can compromise service life,
requiring costly and disruptive interventions that may bring chronic stresses at the
scales of building and urban habitat.
10. Adaptability: As with durability, adaptability is another sustainability attribute
with resilience implications. Planned system maintenance and partial renovations
can be used as a strategy to extend service life. Façade systems designed to
accommodate this strategy will be more durable with less potential to become a
contributing factor to chronic stress patterns in the built environment. Adaptable
systems can more easily accommodate the changing conditions of use that
increase in likelihood of occurrence as service life extends.
11. Recovery: Resilience is not just about absorbing the shocks, but also the ability to
recover quickly, minimizing disruption and cost. These measures of recovery
should be specified as an integral part of risk assessment, e.g., a given building
should be operational within x-days of a x-year flood event, with damages under
$x, and with no loss of life.
12. Health & comfort: The health and comfort of a population is a resilience factor;
healthy people are better able to manage the shocks and stresses associated with
risk events. The building skin directly impacts the health and wellbeing of a
building’s occupants.
6.9.2 Metrics and Strategies for Façade Resilience
The framework supports the identification and development of tools and strategies with
the potential to enhance façade resilience. Where possible, these strategies are
accompanied by processes and metrics that support the evaluation of the various
strategies. The resilience factors cover a broad range of expertise, so the framework

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provides for input from a range of disciplines and experts. The objective of this research
is to suggest relevant examples for each factor in support of the evaluation framework,
not to provide a rigorous listing of all possible strategies and metrics.
6.9.3 Ten Top Strategies to Enhance Façade Resilience
Resilience thinking will lead to the development and identification of many strategies to
enhance façade resilience, along with processes and metrics to support them. The
strategies in Table 6.3 were among those that emerged from the resilience workshop
dialogue, and exemplify the connectedness of the resilience factors with the façade
system, further establishing the linkage between urban resilience and the building skin
that is one of the goals of this research. The strategies included in Table 6.3 are not the
most obvious, detailed, and explicit strategies that dominate the dialogue of engineering
resilience, but more generalized strategies that emerge after deeper consideration of the
relationship of socio-ecological resilience to the built environment. Table 6.4 includes
more of the strategies from the workshops, including more detailed and specific
strategies, although even here no attempt has been made to rigorously and completely
exhaust all possible strategies over the broad range of resilience considerations.
Table 6.3: This collection of resilient façade design strategies is in part derived from the Principles
of Façade Resilience in Table 6.1, and both are a product of this research derived from workshops,
surveys, and literature review as described in section 2.5.4.
10 Top Design Strategies to Enhance Façade Resilience
1. Develop a basis-of-design resilience plan with specific goals for façade resilience.
2. Design to prevent façade system breach.
3. Design for uncertainty and change.
4. Design façade systems to enhance building, occupant, and community resilience.
5. Design for human safety, health, and comfort to enhance resilience.
6. Design for beauty and efficiency; bind aesthetic and performance goals.
7. Consider sourcing and supply chain networks during design development.
8. Design to mitigate system damage from shocks.
9. Design for durability.
10. Design façade systems with adaptive capacity.

1. Develop a basis-of-design resilience plan with specific goals for façade
resilience. Resilience will not be achieved in the absence of clear, specific, and
measurable commitments established early in the design process. As part of the
basis-of-design, prepare a building resilience plan that considers the building

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façade within the context of future conditions of climate, site, building, and
habitat. Adopt a code-plus approach, and performance-based targets (e.g., no
envelope breach in a 500-year event; maintain structural integrity for 5000-year
event, etc.).
2. Design to prevent façade system breach. Prevent façade breach and materials
falling from façade system from extreme wind pressures and impacts from
airborne debris. A breach of the façade will greatly increase the odds of further
damage to the façade system and nearby buildings, and increase the risk of injury
to building occupants and the public. The breach can amplify wind pressures
acting on the façade, and materials separating from the façade system can impact
other areas of the façade, neighboring buildings, and people and infrastructure at
ground level. The use of laminated glass with outboard exposure is a first line of
defense. Enhance infill panel retention (e.g., glass) by increasing framing “bite”
(depth of panel capture).
3. Design for uncertainty and change. Resilient design anticipates future
uncertainty, including the inevitability of surprise. Use evidenced-based research
where relevant, but understand that emergent conditions will likely render much
of this data obsolete. Design using forecast data in areas where historical data may
prove inadequate (e.g., climate). Design for a broad range of contextual outcomes.
4. Design façade systems to enhance building, occupant, and community
resilience. Consider ways that the façade can contribute to greater building
resilience. Façade-integrated photovoltaics, for example, may not enhance the
resilience of the façade system per se, but hold great potential to increase building
resilience in the event of disruptions to the power grid. There is even the potential
for large buildings to be developed as power sources for their local community, a
capability that could help offset the resource consumption represented by these
buildings. At least in the case of tall buildings, this would necessitate activating
the façade systems. Similarly, the façade system may be employed to harvest
rainwater, and even condensate in some areas, that can be used to replenish gray-
water storage that can keep waste systems working during periods of
infrastructure disruption, or even as a supply of potable water if purification
systems are developed.
5. Design for human safety, health, and comfort to enhance resilience. Table 6.1
establishes safety, health, and comfort as considerations of resilience. Beyond
safety issues, this includes indoor air quality, thermal and acoustical comfort, the
balancing of daylighting and glare, the provision of view, access to nature, and
occupant controls over the work area environment. Consider principles of
Biophilia in the design of interior environments, which has been shown to

267
increase productivity in the work environment and speed recovery times in
hospitals (Browning et al. 2012).
6. Design for beauty and efficiency; bind aesthetic and performance goals.
Aesthetics are a source of resilience (Shrivastava 2015; Walker and Salt 2012, 7;
Wilson 2011). Let the constraints imposed by considerations of resilience inspire
the art of the building skin. Beautiful facades will yield buildings valued by the
communities in which they reside, and that will consequently be maintained and
preserved, contributing to durability, extending service life, thereby enhancing
community resilience. Aesthetic considerations, however, must be balanced with
performance. Aesthetics are he predominant driver in façade design today, often
at the expense of performance. This will compromise the long-term resilience of
urban habitats.
7. Consider sourcing and supply chain networks during design development.
Table 6.1 establishes that high levels of customization can compromise resilience.
This is in part because high customization often leads to complex and convoluted
supply chains to satisfy the material and fabrication requirements of the façade
system. System repairs in the wake of shocks can be significantly complicated in
this case, resulting in delays and elevated costs. Certain products may no longer
be available. Locally supplied proprietary materials and systems can present a
similar problem, as the supplier’s capability of delivering remedial products may
be compromised by the same event that caused the damage. Identify materials and
products during design development for which there are multiple sources with
wide geographic distribution.
8. Design to mitigate damage resulting from shocks. Excessive damage to façade
systems resulting from shocks can produce long-term economic stresses that
impact resilience at the broader scale of community, region, and even nation. The
damage to a façade system design can be assessed in the context of a shock of
defined magnitude and type. Set specific design goals that mitigate damage as
part of the resilience plan.
9. Design for durability. Establish a design service life for the façade system in the
context of the building service life, again, as part of the basis-of-design. Perform a
durability analysis of the façade system design parallel with its development,
including the consideration of differential durability of the façade system
subassemblies, components, and materials. Design façade system assemblies for
disassembly. Avoid permanently bonding assemblies wherever possible to
facilitate maintenance, renovation, and repair. Utilize planned cycles of
maintenance and partial renovation as a strategy to extend façade system service
life. The façade system should be designed to see continuous service over the
lifespan of the building. This is an achievable but seldom implemented practice.

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10. Design façade systems with adaptive capacity. The certainty of the unexpected
in the realms of social behavior, climate change, economic conditions, and other
less evident areas of potential influence, brings substantial value and risk
mitigation to façade systems that can be readily adapted in material,
configuration, and appearance in response to emergent conditions. Some changing
conditions can be easily identified but are generally ignored. For example, the
conversion of buildings to support broadly adopted energy consumption goals for
2050 (NYC 2014) will require that buildings under construction today—and into
the next decade at least—future will require retrofit before 2050. They should,
therefore, be designed in anticipation of such a need. An example is the use of a
cassette system to facilitate the easy change out of the glass in a curtainwall
system (Section 8.7.6). Over-design façade anchorage systems.
6.9.4 Façade Resilience Table
The framework is finally used to build Table 6.4: Table of façade resilience factors,
metrics, and strategies. The table is a literal translation of the framework diagrammed in
Figure 7.3. The table is the final product in the development of a framework for
evaluating façade system resilience. The metrics, processes, and strategies included are
intended as examples only. The goal of this research is to build the framework, not to
populate the specific metrics, process, and strategies, which span broad multidisciplinary
considerations involving experience and expertise from many disparate fields of
expertise.

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Table 6.4: Table of façade resilience factors, metrics, and strategies.
RESILIENCE
FACTORS
PROCESSES &
METRICS
CURRENT
PRACTICE (CODE
MIN) TARGET STRATEGIES AND TOOLS
design goals resilience planning rarely included required develop a resilience plan that considers the façade system during
early schematic design
% operational in x-
year event
no known instance of
definition
define performance based target, e.g., 100% operational in 500-year
event; structurally intact for 5000 year event
4

simple façade system functionality with manual overrides for all
automated functions
design loads

codes
standards
International Building
Code (IBC)
adopt a code-plus program–over a model building code–for disaster
resistance; e.g., the IBHS’s FORTIFIED for Safer Business™
wind employ wind tunnel analysis to determine maximum wind pressures
use forecast climate data rather than historical data
detail system for optimal glass retention under extreme wind loading
seismic define performance based target as indicated above in design goals
use lightweight curtainwall systems in high seismic zones; avoid the
use of heavy precast concrete and other masonry
detail system for optimal glass retention under high seismic loading
electrical grid
disruption
utilize grid-isolatable BIPV solutions to mitigate impact of extended
power loss
BIPV façade power production system with grid-disconnect in case of
power outage
Develop electricity independent building ventilation systems
incorporating manually operable windows/vents
storm surge
and flood
design facades, especially sloped surfaces, to manage forecast
stormwater flows
utilize materials and finishes that will not decompose and leach
hazardous chemicals under flood conditions
utilize materials and finishes that will retain serviceability after
exposure to temporary flood conditions
consider secured knock-down walls in known flood and surge zones
consider omitting facades entirely below elevation of projected high
water line
consider a façade integrated rainwater harvesting system
extreme
temperature
as part of whole-building energy modeling—include modeling of drift
temperatures if energy sources for heating and air conditioning fail
consider u-factor, thermal mass, and low WWR to mitigate heat loss
during extended absence of mechanical heating
use heat strengthened glass to prevent stress fracturing under high
temperatures
design façade systems to prevent formation of ice dams that may fall
into public areas, or become airborne debris in high wind conditions
consider exterior shading on south and west elevations in hot
climates
incorporate manually operable windows/vents and shading devices
for use in the extended absence of mechanical cooling
extreme wind design to prevent envelope breach under extreme wind events,
including impact effects of airborne debris and hail
laminated glass primary strategy to
meet South Florida
code for missile
impact resistance
double-laminated
IGUs provide
greatest protection
use impact resistant glazing
fire assure adequate fire-stopping (fire-safing) between floors
consider fire risk from neighboring buildings based on proximity
use materials and finishes that will not outgas when exposed to fire

270
consider use of fire-rated system at lower floors adjacent to
landscaping and on facades in close proximity to neighboring
buildings
security adopt blast design load criteria and security measures at ground floor
durability do formal durability and differential durability analysis
utilize materials, components, and subassemblies that are durable
within the context of forecast future climatic conditions
adaptability adaptability enhances resilience; see parameter 5
provide manual overrides for all automated façade system elements
(blinds, louvers, vents, etc.)
design curtainwall infill panels to be easily replaceable from inside the
building
recovery:
water,
electricity,
HVAC, waste
disposal,
envelope
breach
hours/days to
restoration of
critical services
days to full
recovery
have a plan for the rapid acquisition of all materials and products in
the case of widespread damage (think readily available and local)
design for a simple and local supply chain
design for disassembly
minimize the use of complex operations-critical systems and exotic
materials
glass supply can be problematic in lead times; develop contingency
plan for delayed material supply
economic
impact
$$$ economic impact of extensive property damage can potentially delay
recovery for months or years, hobbling communities, cities, and even
nations. design to minimize damage resulting from property risks
health &
comfort
human health is a resilience issue, with the façade a contributory
factor
control glare inside and outside; external glare from highly specular
surfaces can pose a safety risk

4
The Insurance Institute for Business & Home Safety 2013. Code-plus programs for disaster resistance. Whole Building Design Guide, The National
Institute of Building Sciences. Accessed 26 January 2015: http://www.wbdg.org/resources/codeplusprograms.php

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6.10 Summary
Resilience is conceptually complex. Using the terminology of Holling and others in the
Resilience Alliance, the widespread uptake of the urban resilience dialogue largely
involves considerations of engineering resilience, while the more nuanced aspects of
ecological resilience are neglected. This is understandable. The engagement of urban
communities with resilience practices has much to do with the immediacy and tangible
effects of disaster related shocks, unlike the abstractions of invisible greenhouse gases
and impacts that unfold over years and decades. And there is no doubt about the
importance of improving the engineering resilience of urban communities. To ignore the
considerations brought to the forefront by the concept of ecological resilience, however,
threatens a critical opportunity to engage urban resilience at far greater depth.
Resilience has been considered here in terms of the immediate impact of shocks as well
as the long-term effects of stresses, which can result from the shocks or from more subtle
causes. Considerations of engineering resilience and ecological resilience have both been
explored. The relevance of spatial scale to considerations of resilience has been discussed
at the progressive scales of building system, building, and urban habitat. The organized
efforts to enhance resilience—efforts taking place at various levels of governance ranging
from community to nation—have understandably focused on the mitigation of, and
recovery from, shocks produced by natural and anthropogenic disasters. Consideration of
temporal effects at the spatial scales, however, reveals the potential for a more subtle and
insidious threat to communities, and ultimately, nations. Such temporal effects are
represented by the stresses induced by attributes of durability and adaptability over
extended time periods.
Like sustainability, the concept of resilience is comprised of multiple factors that must be
considered as an integrated whole; ignoring any single factor in a design or assessment
diminishes the probability of a resilient outcome to a new building project or major
renovation, or the quality of an evaluation of resilience in an existing building or building
system. An attempt has been made here to establish the primary factors of building
façade resilience in the larger context of urban resilience. Resilience concepts have been
examined from multiple disciplines, with a particular focus on socio-ecological science

272
where many of the core concepts have developed, to be later reinterpreted within a broad
range of disciplines. This exploration was fruitful in highlighting important
considerations when evaluating resilience, considerations that are not typically part of the
urban resilience dialogue or practice.
The winds and floodwaters brought by severe storms are common resilience
considerations; durability and adaptability of the façade system are seldom considered in
resilience planning. Resilience thinking (section 6.5.1) integrates important concepts of
redundancy, adaptive capacity, simplicity, and others, into a holistic systems view that
can be productively brought to focus on the built environment. This research has explored
ideas and developed observations regarding generalized principles of resilience, and
weighed their relevance to the built environment, buildings, and ultimately, to the
building skin. The outcome of this research includes the following:
§ The development of resilience principles relevant to the façade system as
represented in Table 7.1.
§ The definition of 12 resilience factors as shown in Figure 7.4 and Table 6.2.
§ The identification of resilience strategies, including a select group of 10 in Table
6.3.
§ The development of a table integrating factors, metrics, and strategies as
conceptualized in Figure 7.3 and represented in Table 6.4.
Performance considerations dominate building energy retrofits, but when it comes to the
façade, appearance is the primary driver (Section 8.6.4). This is problematic, as façade
renovation is typically excluded in building energy retrofit projects because of the cost
and disruption involved in the façade retrofit process. But it also points to the fact that
image—as established by façade appearance—is a driving consideration in how buildings
are valued. Buildings that are valued by the owner, occupants, and community, are more
likely to be maintained and regularly updated to current standards, including resilience
standards. The facade makes a unique contribution to building aesthetics, adding another
dimension to the role the façade plays in resilience across physical scales of urban
habitat.

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Chapter 7 — Vintage skins: Retrofitting the tall face of
Modernism
7.1 Introduction
Adaptive renewal remains the only means to unfetter future generations who
will otherwise inherit dysfunctional building technologies that tether the human
imagination and diminish the earth. Kesik and Saleff (2009, iv).
Building reuse, repurposing, and rehabilitation are inherently sustainable endeavors (de
Jonge 1996, 8; Richards 2015, 140), avoiding demolition waste and the embodied carbon
of new construction. Many studies have recognized that the building industry has the
greatest potential for carbon reduction, with current technology and at minimal cost
(UNEP 2011; UNEP 2014; Bernstein and Russo n.d.). Yet the opportunities presented by
the existing building stock have received little attention (Frey et al. 2011, 84). Studies
(Frey et al. 2011; Langston et al. 2008; Total Carbon Study 2015) suggest that existing
building upgrades produce fewer negative impacts than building replacement (with rare
exceptions [Frey et al. 2011, 8]), but that design and material strategies are of critical
importance to optimal outcomes: energy efficiency must be optimized, and material
selection and quantity can reduce or negate the benefit (Frey et al. 2011, 89).

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This chapter explores current façade retrofit practices for TCBs and finds that they
generally fail to support sustainability objectives for buildings and the built environment.
Among these findings, TCB retrofits:
§ fail to account for embodied impacts
§ fail to anticipate and accommodate the need for future façade renovations
§ lack the adaptive capacity to avoid premature obsolescence,
§ fail to provide durability and service life behavior commensurate with the
commitment of resources required by their construction.
The benefits of building and building system reuse are discussed in Section 7.3. The TCB
is found to problematic in ways that potentially compromise reuse and may necessitate
building replacement, and indictment of early design practices for this building type. The
TCB is compared to another building type, the Multi-Unit Residential Building (MURB)
to highlight the differences and their implications in Sections 7.31 – 7.34. Ultimately, the
sustainability of the TCB building type is questioned in Section 7.3.5.
Key considerations of the façade renovation of TCBs are identified and discussed in
Section 7.4, followed by a proposed typology of façade renovation strategies for this
building type. Case study examples follow for each type (Sections 7.5.4-7.5.6). These are
followed by a case that investigates the special considerations of heritage buildings
(Section 7.5.7).
The dominant tendency of reclad as a TCB renovation strategy is problematic in several
respects, as a carbon-intensive solution, and as a potential threat to health and
productivity as well as heritage value. These are discussed in Section 7.6. New
trajectories for future TCB façade renovation are suggested in Section 7.7).
The perspective of the preservationist is informative, and is further explored in Section
7.8). The concept of renewable systems developed in Chapter 4 is integrated with
considerations of TCB façade renovation in Section 7.9. Guidelines for sustainable TCB
façade renovation are suggested in Section 7.10, followed by a summary discussion in
Section 7.11.

275
The following section discusses the TCB building type and history, and establishes the
context for the investigation to follow.
7.2 Context
The tall glass curtainwall building typology of the twentieth century is an icon of
Modernism. Architects producing these icons included Mies van der Rohe, Le Corbusier,
Oscar Niemeyer, Minoru Yamasaki, I.M. Pei, Gordon Bunshaft, and many others. The
better-known icons include the UN Secretariat Building (Le Corbusier, Oscar Neimar,
Wallace Harrison et al., 1952), Lever House (Gordon Bushaft and SOM, 1952) and the
Seagram Building (Mies van der Rohe, 1956-58) in New York City, the National
Congress of Brazil in Brasilia (Oscar Niemeyer, 1957-64), and again, many others. These
early icons inspired a new vernacular of tall curtainwall buildings (TCBs) of a notably
lesser quality (Wigginton 1996, 96).
Lost amidst the current unprecedented global boom in tall building construction is that
the earliest of this building type dating back to the mid twentieth century are now fifty
years of age and more, in service far longer than their builders anticipated (Browning
2013). Some few have undergone major renovation. The large majority have not, and
represent a looming need for renovation on an urban scale. A defining characteristic of
these Modernist glass towers that so quickly redefined the skylines of major urban areas
in the U.S. and Europe is the modular metal and glass curtainwall, combining both the
face and enclosure of these buildings, defining both building skin and urban habitat. As
these buildings have aged and become the focus of rehabilitation considerations, this
façade system typology has proven to be a significant renovation challenge (Henket
1996, 14).
Both the need and the complexity of curtainwall retrofit on vintage TCBs is amplified by
the dramatic change in performance expectations since their construction. Energy
conservation, thermal and acoustical performance, solar control, daylighting, and
ventilation requirements have evolved well beyond initial parameters. In addition, the
conditions of use have changed. Urban environments have grown increasingly dense,
along with noise, light and air pollution. As it turns out, curtainwall system designs have
proven very poorly equipped to adapt to these changes (Section 4.3).

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Many of these buildings were constructed during the post-war building boom in the mid
twentieth century, a period of cheap energy prices characterized by little consideration for
energy performance, and a time when building science was poorly understood and
seldom applied. It was also a period of experimentation with emergent and unfamiliar
systems and materials (Wigginton 1996, 3.94-3.96; Ayón and Rappaport 2014, 18).
These factors, combined with a construction ethic that anticipated building lifespans as
limited to a maximum of 30 years, resulted in buildings of poor quality and limited
durability, buildings that were poor performers from the beginning and that have not aged
well. These buildings are now 40 to 50 years old and more and comprise a significant
percentage of the commercial building sector in urban zones like Midtown Manhattan
(Rappaport and Sigge 2004). The sheer quantity of these buildings renders it impractical
to consider their demolition and reconstruction as a standard practice. Rather, it is
imperative that efficient methods are developed to significantly prolong the lifespan of
these buildings. Consequently, goals for future reductions in energy consumption and
related carbon emissions must be built on a foundation of improvements to the existing
building stock (Elefante 2007).
The opportunity is significant. Richards (2015) describes the rejuvenation of tired
buildings as the “realignment of a building’s durability with long-term economic value.”
Tishman Construction, one of the largest general contracting firms operating in New
York City, has a “building repositioning” team specializing in existing building
renovations. The team’s director notes, “There are 440 million square feet of commercial
space in New York City. Of that, about 70 percent was built before 1980. The current and
future market is in transforming these buildings to be energy efficient, sustainable,
marketable, and updated” (Hauserman 2016). Unfortunately, TCBs are proving
particularly challenging whole-building renovation candidates.
Curtainwall technology and its application developed rapidly in the mid twentieth
century. These new lightweight cladding systems gained swift market adoption as an
alternative to the masonry infill wall practices of the time. Combined with the use of
passenger elevators and air conditioning systems, this new technology owed its initial
success to the embrace of the real estate development community, which recognized the
benefit in the increased leasable floor area provided by the thin cladding systems
(Wigginton 1996, 96). Multiplied by each floor, this advantage was significant, and
served as one important aspect in the emergence of the tall building form.

277
Built principally for office buildings in the days of cheap and abundant energy, energy
efficiency and comfort were not predominant concerns of TCB design and construction.
They were also realized amidst an emerging throwaway culture in which the lifespan of
even a tall building was regarded as perhaps 20 years (Browning 2013), eliminating
considerations of durability and service life as design drivers. Despite the advancing age
of these early applications, relatively few have undergone façade interventions of any
significance (Patterson and Vaglio 2011a). There are good reasons for this; it turns out
that the tall curtainwall building presents a particular challenge when it comes to the
renovation of these exterior wall systems. Cost and, even more, disruption to ongoing
building operations, act as significant barriers to façade interventions in this building
type. Even the relatively recent trend of building energy retrofits that has found traction
in the commercial building sector frequently stops short of addressing holistically the
unprecedented challenge of retrofitting the curtainwall. In many instances, the low-
hanging fruit of HVAC and lighting systems are upgraded while the aged, substandard
façade systems are left intact (Olgyay and Seruto 2010; Hart et al. 2013). With this
limited approach, the opportunity for optimizing energy performance and comfort
through the integration of the major building systems is lost, with the very real prospect
that the façade system will soon require major repair or replacement in any case. Deep
energy retrofitting necessitates consideration of the building envelope (Killien 2011; Hart
et al. 2013) and in the case of older TCBs, it generally requires a significant level of
intervention with the facade system.
There is also emerging recognition of the potential heritage value of the TCB building
type (Ayón and Rappaport 2014). Appreciation for the “glass box” tall curtainwall
building as an expression of Modernism has waxed and waned since the time of its
widespread appearance in the 1960s, and opinions vary widely among owners,
professionals, the public and academics alike as to its cultural value. Some of the older
curtainwall buildings are clearly an important part of the heritage of Modernism and
deserving of preservation. Iconic and landmark buildings like Lever House and the
Seagram Building are easily singled out in this respect (Figure 7.2).

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Figure 7.2: Iconic and landmark buildings like Lever House (left) and the Seagram Building, which
share the same intersection on Park Avenue in Manhattan, are easily identified as among the
heritage of Modernism. (Author’s photograph.)
Less significant manifestations of this architectural
style are abundant and in need of façade renovation.
These buildings are integral to the texture of urban
habitat and their contextual contributions and
character-defining presence has been thoroughly
documented in commercial areas such as Midtown
Manhattan (Figure 7.2), where more than two
hundred modern curtainwall buildings were
recorded in a survey performed by the local
Docomomo chapter (Rappaport and Sigge 2004,
113). There is a growing awareness of the
vernacular value of these buildings, and calls for
increased protections including landmark
designations continue to arise (Jerome 2014). The
recent designation as a New York City Landmark
of the Citicorp Center at 601 Lexington Avenue
(Hugh A. Stubbins, Jr., Emery Roth & Sons, and
E.L. Barnes, 1974-78), however, is an interesting

Figure 7.1: The character of urban
habitat in areas like Midtown Manhattan
is deeply influenced by the early
Modernist glass and metal curtainwall
buildings. (Author’s photograph.)

279
development in the saga of the rezoning of Midtown Manhattan. As landmark petitions
for other Modern buildings in the area languish, this designation reinforces the notion that
only the high-profile examples of this building type will be preserved and that many tall
vernacular TCBs will likely remain unprotected and subject to significant alterations for
years to come.
In the United States, some relevant discussions have started to take place within the
framework of preservation scholarship, advocacy and research. A roundtable discussion
on the rehabilitation of curtainwalls organized by Docomomo NY/Tri-State in 2013
brought together several practitioners in the subject to discuss some of the more relevant
challenges (Ayón and Rappaport 2014). A symposium—Renewing Modernism –
Emerging Principles for Practice—organized by the APT’s Technical Committee on
Modern Heritage and Technical Committee on Sustainable Preservation and conducted
during the APT 2015 annual conference in Kansas City catalyzed important discussion on
the renovation of Modern glazed facades, as well as emerging principles and best
practices for intervention. Outcomes of these events included
§ recognition that conflict between preservation and sustainability goals must be
evaluated in a case-by-case evaluation,
§ cases must be differentiated between landmark quality and the vernacular,
§ the Modernist aesthetic expressed in these early TCBs is not well understood or
appreciated by building owners, leading to façade upgrades embracing a “new
look,”
§ more research is needed to develop technical solutions for the façade retrofit of
the early single-glazed TCBs that accommodate the retention of the original
aesthetic to the greatest extent possible (ideas suggested included intrior storm
windows, shading devices, glare/UV protection films, and window inserts),
§ the “inventiveness” of the façade technology should be part of the case-by-case
assessment,
§ and a general agreement that preservation considerations and practices should be
included alongside performance objectives.

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Complicating considerations of cultural significance and heritage value are multiple
factors discussed in section 7.3, but an overarching consideration is the environmental
impact of the building sector. Climate change effects have brought increasing urgency to
building energy consumption and resulting greenhouse gas emissions, and produced a
growing realization of both the operational and embodied impacts comprising a
building’s eco footprint. The push is on for net-zero (Peterson, Torcellini and Grant 2015;
NBI 2017) or net-zero-ready (DOE n.d.) performance in commercial and large
multifamily residential buildings, with respect to an expanding array of impacts including
energy, carbon, water and waste. Existing building enclosures must ultimately be
retrofitted, and in particular the many that are known to have high energy consumption
and poor thermal performance, as with the vintage TCB stock. Assessment of heritage
value and the development of preservation strategy for any given building must be
undertaken in support of appropriate resilience and sustainability goals at the local,
regional, and national scales. The preservation of buildings and urban habitat is an
important component of the sustainability dialogue, but it is one among many that must
be balanced against each other to achieve successful outcomes.
7.3 Replacement versus rehabilitation
Many have claimed that the existing building is the greenest building (Elefante 2007;
Moe 2010, loc. 135; Roberts 2007, 1), and Frey et al. (2012) has provided supporting
evidence for generalized building types. The case for existing buildings is also discussed
in section 3.1.5. The building stock is comprised of many different types with wide-
ranging characteristics, and few have been rigorously analyzed in the manner of Frey.
More needs to be known to determine if early Modern curtainwall buildings are generally
reusable. The above considerations begin to suggest that tall curtainwall buildings falling
short of landmark status may be unfit for renovation. This was the thrust of a recent
report stemming from a study of this building type in New York City (Browning et al.
2013). The report urges consideration of zoning changes that would encourage, under
certain conditions, the demolition of existing buildings and their replacement with larger
buildings that embody a more viable financial model for the developer. Many researchers
now emphasize the importance of quantifying the environmental impact—including
embodied impacts—in such assessments (Cabeza et al. 2013), a practice that remains
relatively uncommon even with projects that have embraced sustainability goals

281
(Timberlake 2015; Trabucco and Fava 2013, 42; Stein 2010, 35). The façade system is a
factor, and can play a decisive role, in the assessment of building replacement versus
rehabilitation; the cost, disruption and risk that accompany a façade replacement may
encourage building demolition and reconstruction as a viable alternative.
In comparing replacement versus rehabilitation of the TCB façade system, one of the
apparent problems with curtainwall systems is a lack of options when it comes to
renovation. Successful partial renovations are possible, as demonstrated by the façade
renovation of 60 Broad Street in New York City (Section 7.5.7) discussed following. But
short of such remedial interventions—repairs and temporary fixes to squeeze out another
period of service but providing minimal performance improvements—the costly and
disruptive path of complete façade system removal and replacement appears to be
commonplace. Façade intervention strategies for vintage TCBs are discussed in section
7.5. The rehabilitation challenges presented by vintage TCBs as a building type are
further discussed in the following section.
7.3.1 A tale of two building types
The following is a comparative analysis of two building types: one, the vintage TCB and
two, the multi-unit residential building (MURB). The analysis is useful in articulating
inherent challenges posed by TCBs, which provide very limited options for renewal, and
emphasizing the critical importance of robust façade systems in TCB applications,
retrofit-ready and with built in adaptive capacity.
The threat of building demolition in TCBs has been noted. The following section
investigates the history, attributes and retrofit opportunity of two vintage (1960-1980)
building types to see if their comparison can inform façade retrofit opportunities and new
building design. One is TCBs as an office typology in Manhattan, the other a multiunit
residential typology found predominantly in the Toronto area. The former presents
significant barriers to rehabilitation, while that latter appears an ideal candidate.
It seems intuitive, given the massive waste generated by building demolition and equally
massive commitment of resources involved in new building projects, that renovating an
existing building would support sustainability goals better than demolishing and
rebuilding, and in fact, studies tend to bear this out (Adlerstein 2016; Trabucco and Fava
2013; Frey et al. 2012; Sloman and Edwards 2012). But renovation is not free, requiring

282
significant economic and embodied energy expenditures. While this research makes the
case that building demolition and replacement should be a strategy of last resort, not all
buildings are fit for major renovation. There are unique retrofitting challenges presented
by TCBs as a building typology, especially the vintage forms as represented in Midtown
Manhattan, and there may be reason to question their fitness for major system upgrades.
TCBs represent a significant retrofit opportunity with respect to energy performance.
Designed at a time of abundant resources and cheap energy, the early curtainwall systems
through the 1970s were single-glazed, thermally unbroken and never good energy
performers. The problem is endemic to glass and metal curtainwall technology; even
recently built LEED certified TCBs have been revealed as poor energy performers by
New York City’s new mandatory reporting requirements (Table 3.1). Glass and
aluminum are both highly conductive materials, and managing thermal heat transfer has
been a challenge from the beginning of their use as predominant curtainwall materials.
TCBs are synonymous with the extensive use of vision glass, and while considerably
improved, even high performance glazings do not approach the insulation values of
opaque insulated wall systems. Glazing performance has improved over the past
decades—double-glass products were slowly adopted after the 1970s oil crisis—largely
through the development of low-e and solar coatings that greatly improved insulation and
solar behavior. The focus then shifted to the aluminum framing systems, which can easily
represent 10-15 percent of curtainwall surface area. Air and moisture infiltration continue
to be a concern with curtainwall performance. Today’s curtainwall systems are far
superior to the early applications, and retrofitting vintage TCBs with new curtainwall
systems seems an obvious opportunity.
Pre-war era masonry buildings were designed with high windows for daylight, natural
ventilation, and thick walls provided thermal mass that moderated internal temperatures.
Consequently, these buildings are often found to be better energy performers than
modern LEED rated TCBs (Browning 2013, 17-18). Table 7.1 compares energy data for
a few office and residential buildings from different eras and with different façade types.
A problem with mandatory energy reporting requirements is that considerations of
occupation density or use are not factored into energy use intensity (EUI) data: trading
floors, data centers, and other usage consume excessive amounts of energy and may skew
simple comparison. Still, it is interesting that the oldest building in the table is also the
highest performing.

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7.3.2 Vintage Midtown Manhattan tall curtainwall buildings
Browning et al. (2013) published a research report considering the challenge of deep
retrofits to TCBs, using an existing building—675 3rd Ave., (included in Table 3.1)—as
a control sample, and comparing it to a theoretical replacement building designed to take
advantage of market economics with a 44 percent increase in leasable floor area. They
researchers concluded that
1. Well maintained buildings of this type with low level upgrades can best the
national average by perhaps 10 percent.
2. Deep energy retrofits involving more aggressive interventions could reduce
energy consumption by over 40 percent, but don’t work financially.
3. A high-performance replacement, with 44 percent greater floor area, could
provide marginal energy reductions (5 percent) with increased occupancy,
providing economics that would work for the owner-developer.
The problem is with the characteristics of the building designs beyond the façade
systems, primarily having to do with low floor-to-ceiling heights and small bay widths,
which cut down on the available façade effects of daylighting and view. This drops the
buildings out of the class A property category down to B or C, with corresponding lease
Table 7.1: Manhattan buildings data disclosure (NYC 2017).
name type year façade type floors
Site EUI
(kBTU/sf)
Source EUI
(kBTU/sf)
energy
star rating
(2016)
Empire State
Building
office 1930
masonry &
windows
102 83.1 189.8 84
Lever House office 1952 curtainwall 21 137.7 337.0 24
Seagram
Building
office 1958 curtainwall 38 220.0 485.9 7
MetLife office 1963 precast curtainwall 59 124.5 262.3 55
675 3
rd
Ave office 1966 curtainwall 32 116.3 235.5 60
New York Times
Building
office 2007 curtainwall 52 152.4 285.1 57
250 W 55th office 2013 curtainwall 42 58.8 145.7 87
Trump Place residential 2001 window wall 54 102.6 161.9 14
Astor Place residential 2005 curtainwall 21 130.3 196.1 3
Trump Soho residential 2010 curtainwall 46 132.4 298.6 16

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rates that effectively prohibit financial return on a deep energy retrofit investment.
Payback period was estimated by the research team at 44 years.
The façade renovation for the deep retrofit, at $100 per square foot, is quite nearly the
cost of a new double-glazed thermally broken façade system, not counting demolition
(Kaisersatt, 2014). It was determined that the existing building structure could not
support the additional dead load of a new thermally broken double-glazed curtainwall
system; the building was designed to only 30 psf wind loads. The façade retrofit was
apparently limited to an upgrade in the vision glass areas to a high-performance single
glazing with a low-e coating, which still resulted in a 44 percent energy saving, and this
is with an existing well-maintained building; the savings would be more with many of
this building stock. Nonetheless, financial and technical barriers represent a serious threat
to the renovation of this building type, which may result in building replacement. While
not noted in the report, the included cost breakdown for the deep retrofit revealed that of
the façade upgrade cost, which also included a mechanical system upgrade, was nearly 80
percent of the total cost. This supports the contention the current research that these
façade system designs are the primary culprit in the problems presented by the renovation
of TCBs, and increase the probability of building replacement.
The research team also looked at the embodied energy issue (Browning 2013, Appendix
G), developing a model that suggested a net expenditure with the replacement scenario
that would be recovered within 15.8 to 28 years, but this is based on questionable source
data. Depending on the data used by the team, the recovery period ranged from 15.8 to
263 years. The report acknowledges the use of 30-year old lifecycle inventory data in
deriving the embodied energy values in MBTU per square foot, and notes the lack of
clarity in underlying source data for the various sources, concluding that, as a
consequence, embodied energy considerations are limited in support of arguments for
building preservation. This reasoning here seems spurious; lifecycle assessment (LCA)
tools, methods and data sources have improved considerably in recent years, and it would
be of some value to revisit this important analysis for 675 3rd Ave. The disruption
associated with building demolition and new construction is under played, presumably
because retrofit options will have their own disruption, but potentially of a lesser order
than building replacement. Construction demolition and debris waste is down played with
the rationale that virtually all materials can be recycled or down-cycled, and proposed a
solution for down-cycling the glass for use as concrete fill. Recycling is not free, and

285
down-cycling is only one step above landfill disposal. The embodied energy and great
potential durability of glass is lost when down-cycled.
The report seems intent on making the case for consideration of a zoning change that
would permit the FAR on which the new building model is based, allowing construction
of a building with 44% more floor area. But, as can be seen in Table 7.1, the Energy Star
rating for an acknowledged well-maintained TCB at 675 3rd compares favorably with
recent LEED rated TCBs like the New York Times Building. The building includes only
modest enhancements credited with achieving this performance. With respect to the
façade system, these upgrades included only retrofit window films and caulking. The
investigation of further “low-tech” upgrades could produce results of interest; there is no
sense in the report that this avenue was exhausted of even rigorously investigated. Given
appropriately weighted consideration of embodied carbon and the time-value of carbon,
and building replacement as a strategy of last resort, such an investigation could well
result in a reconsideration of the report’s recommendations.
7.3.3 Toronto’s multi-unit residential building towers
In contrast to the Midtown Manhattan TCBs, Kesik and Saleff (2009) have identified and
developed a compelling case for the renewal of a very different building typology as an
ideal candidate for a comprehensive strategic renovation program: the multi-unit
residential building (MURB). The differences between the two building types may help
to illuminate the shortcomings of TCBs as renovation candidates and possibly reveal
some opportunities for rethinking the TCB façade retrofit.
The MURB typology emerged during the post-war building boom, at the same time as
TCBs. Towers in the park is a modernist vision of the high-rise apartment (Figure 7.3)
that parallels the tall curtainwall office building form. The MURBs are high-rise towers
characterized by a high degree of similarity and consisting of concrete structural frames,
with shear walls in six meter bays, and easily accommodating one-to-four bedroom
floorplans. While the MURB typology was used nearly exclusively for very low-income
families in the U.S., they were embraced by a widespread demographic in Canada,
particularly in the Toronto area where more than 1000 were built between 1960 and
1980, promising forward lifestyles and a new-age alternative to the traditional walk up
apartments. Tower design development quickly converged in size to the limits of fire
code allowances and structural system capabilities of about 36 stories.

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Figure 7.3: Jane Exbury Towers. (Photo: Archives of Uno Prii.)
Planned for 30-year lifespans the MURBs are now into their sixth decade and in a state of
neglect, disrepair and general deterioration. They suffer from the same cheap energy and
throwaway mentality noted with respect to TCBs and are extremely energy inefficient.
Exposed slab edges and thermally unbroken concrete balconies act as heat-sinks,
significantly compromising thermal efficiency. Window and glass door systems are
single glazed and thermally unbroken. Like the tall curtainwall office buildings, the
MURBs are not providing the intended level of service quality to occupants. Nonetheless,
this building stock is not remotely obsolete, benefitting primarily from a more robust and
durable concrete structural system, and a more adaptive structural design, than the steel
structures of the vintage TCBs. The author’s comment (Kesik and Saleff 2009, 8):
When evaluated through the lens of ecological impact, the embedded energy
contained within this extensive building stock is substantial. Demolition would
be an incredible waste of resources.
In evaluating rehabilitation strategies for this building form, Kesik and Saleff see the
relationship between the skin and structural system as central, and recognize an analogy
between building and biological skin. In protecting the building/organism, skin is
exposed to elemental stresses and subject to deterioration. As skin wears out it must be
easily renewed. The building skin is perceived as a dynamic, renewable system to be
optimally accommodated by the building structural system. A service life of 250 years
5
is

5
The authors express an expected service life for the concrete structural system of “several hundred years” but assume
250 years for the proposal.

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assumed for the structural system and 50 years for the façade system; the skin is intended
to be renewed with new materials, finishes, and updated components a minimum of 4
times during the service life of the building. Other building systems and the connections
between structure and skin must be designed for the same building service life, or to be
easily accessed and replaced, this a matter of harmonizing differential durability. The
authors note that this strategy transcends rehabilitation of existing buildings to inform the
design of new high-performance buildings (Kesik and Saleff 2009, 1).
7.3.4 Comparison of TCB and MURB Building Typologies
The significant advantages presented by this vintage MURB building stock are many:
1. robust structural systems with great residual service life,
2. a basic design with the adaptive capacity to avoid obsolescence (in this case,
structural configuration and floorplates that easily accommodate 1-4 bedroom
habitations),
3. a large quantity of highly similar buildings,
4. great potential for significant performance increases with relatively minimal
effort, meeting or exceeding typical new green building performance,
5. surrounding green space eases logistics of construction,
6. hundreds of units per tower make the revitalization strategy economically viable.
In comparison, the TCB stock is characterized by:
1. minimal structural steel framing systems that are under designed by today’s
standards, with some unable to handle the additional dead loads of single to
double glazing upgrades,
2. a basic design with low adaptive capacity characterized by 20-foot bays and low
floor-to-ceiling heights,
3. a large (but lesser) quantity of buildings with enough variation between them,
especially with the façade systems, to require retrofit assessment and strategy on a
case-by-case basis,
4. limited opportunity for performance increases equal to new green building
standards,
5. dense urban environment creates major logistical issues of construction,
6. without elevating the buildings to class A, a revitalization strategy may not be
economically viable.

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The advantages of the MURBs allow Kesik and Saleff the opportunity to look beyond the
renewal of a single building, to a seamless integrated retrofitting process rapidly and
predictably transform the large existing stock of MURBs. The attributes of the TCBs, on
the other hand, present barriers to the conception of such a process. The fault is largely in
the initial building designs. A building that lasts 50 years, with the most recent 20 years
below the minimum service level, and providing no viable means for its rehabilitation, as
with 675 3rd Ave. discussed in the previous section, challenges any notion of sustainable
building performance, even disregarding energy consumption. Yet their wholesale
replacement will produce a heavy economic and environmental burden. Alternate
solutions must be exhausted before resorting to demolition and replacement.
Potential energy use reductions of up to 50 percent are expected from MURB upgrades.
The modeling of the deep energy retrofit for 675 3rd Ave. predicted a 44 percent
reduction in energy use, even with the limitation of single-glazing—if the technical and
financial barriers can be overcome. Combined with an increasing supply of sustainable
energy, a deep retrofit strategy could provide steep reductions in carbon emissions among
the TCB stock. The fact that there are no obvious off-the-shelf solutions to the problem of
revitalizing vintage TCBs does not mean that such solutions cannot be developed.
The comparison of TCBs and MURBs reinforces the findings in section 7.11.
7.3.5 Is the TCB a sustainable building typology?
The following uses the foregoing as a contextual framework to discuss general
considerations of the sustainability of tall curtainwall buildings.
The sustainability of the tall building is an ongoing debate, one of the most interesting in
architecture. Roaf et al. (2009, 237) and others (Massey 2013; Sturgis 2016) challenge
the sustainability of tall buildings. Yet the building type has many champions (Yeang
2002; Leung and Weismantle 2008; Ali and Armstrong 2008; 2010). There is ample
evidence of sustainability pursuits in the design of recent tall building projects, and
general acknowledgement that the current generation is far superior to the vintage TCBs.
Even the authors of the Mid-century (un) Modern report (Browning et al, 2013) discussed
above do not condemn tall buildings, recommending the replacement of the vintage
models with new, larger high-performance models. The conditions of use have also
changed considerably since the mid-twentieth century, when tall buildings were

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predominantly used in office applications. New London Architecture (NLA 2014) reports
that 230 tall buildings are to be constructed in London, with 80 percent intended for
residential blocks. Residential towers have proliferated in urban centers like London and
New York City in recent decades.
Adrian Smith (2016), designer of two of the world’s tallest buildings, believes even
supertall buildings to be inherently sustainable, predominantly owing to the land use
benefits of high density; “Simply put, supertall buildings foster the opposite of urban
sprawl.” He notes two areas where tall buildings are inferior to low-rise; structural
efficiency and embodied energy, noting that towers are made of concrete and steel, and
the small buildings often of wood.
The tall building type faces some intrinsic hurdles (Ijeh 2015). Pointing directly to these
same weaknesses noted by Smith, Sturgis (2017a) finds tall buildings inherently
inefficient, “The higher you go, the more inefficient the building becomes in terms of the
net area measured against carbon emissions from operation, construction and
maintenance.” Sturgis insists that tall buildings lack resilience, and a lifespan to justify
their cost, specifically singling out the curtainwall systems as having a service life of only
40-50 years. He also notes that materials should be fully recyclable, and proposed tall
building projects should be required to provide a “detailed whole-life carbon analysis and
operate with an embodied carbon threshold.” Table 7.2 summarizes pros and cons of the
tall curtainwall building.

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Structural engineers have a small material set to work with: masonry, concrete, steel and
wood. Early tall buildings were constructed of load-bearing masonry that restricted
building height, but were pushed to the limit, as with the Monadnock Building (1893,
Chicago, Burnhan & Root; Holabird & Roche). Steel and concrete enabled the escalating
building heights to follow, and a new tall mark to be realized with the Smith designed
1000 meter Jeddah Tower currently under construction, expected completion 2020. Like
masonry, wood has limitations as a structural material in tall building applications. As
building technologies progress, there is potential for some ideal threshold of height where
wood contributes to a sustainable tall building solution. A survey (Summary Report
2014) conducted by Perkins+Will examined ten “tall” international timber-frame
structures ranging from 7-10 stories, built between 2008 and 2013. The report concluded
that these projects demonstrated mass timber as a successful and emerging construction
method, both high-performing and cost competitive, and the stakeholders involved in
these projects as early adopters. Current applications include the 18-story Brock
Commons (2016, Vancouver, Acton Ostry Architects), the current tallest, to be succeeded
by the planned 19-story Terrace House (Vancouver, Shigeru Ban Architects), and of
course the relentless push for escalating height is on (Stinson 2017).
Table 7.2: A summary of pros and cons of the tall building type (derived from Sturgis 2017a;
Smith 2016; Ijeh 2015).
Proponents claim tall buildings:
• reduce urban sprawl
• promote sustainable transportation alternatives
• enable efficient district-scale energy supply
Opponents counter-claim:
• there are better ways to achieve density
• negative social impacts of dense clusters of luxury
condominiums
• stress on urban infrastructure
• high energy use intensity and carbon emissions
• high lifecycle embodied carbon
• open balconies become problematic
• natural ventilation if a major challenge

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The premium for height
Tall building pioneer and leading tall building architectural firm Skidmore, Owings &
Merrill developed a hybrid mass timber structural concept for a 42-story building that
minimizes the carbon footprint. The project, funded by the Softwood Lumber Board, is
documented in a report (SOM 2013), and addresses tall buildings and sustainability,
acknowledging that the embodied carbon footprint of a tall building is significantly
higher that low-rise on a unit floor-area basis, what they refer to as the “premium for
height,” a measure of both cost and carbon. The reason is attributed to the structural
system as responsible for most of a building’s embodied carbon and the requirement of
far more structural material to support a tall building. The primary contributor of carbon
emissions is found in the production processes required to produce the structural
materials. The report recognizes two ways to reduce embodied carbon; first is to use less
material, already a driver of tall building structural design, the second is again back to
material selection, and the use of a material with less carbon intensity.
Researchers have validated the embodied carbon benefits of wood (Buchanan and Levine
1999; Petersen and Solberg 2002). Lower energy requirements to support the production
process for structural grade wood is the primary advantage. Wood also has the advantage
of actually sequestering carbon through the process of photosynthesis, absorbing
atmospheric CO2, separating and releasing the oxygen and storing the carbon; wood is
approximately 50% carbon by weight (Ehrlich 2013). The wood acts as a carbon sink for
the lifespan of the material, only releasing the carbon back into the atmosphere through
decomposition or combustion. Cabeza et al. (2013) point out that the low fossil fuel
requirements in manufacturing are far more effective in lowering the lifecycle carbon
footprint.
There will be limits to tall with a mass timber structure. To push these limits, Green and
Karsh (2012) authored The Case for Tall Wood Buildings, which develops a scheme for a
largely mass timber structural system capable of reaching 30 stories. SOM developed a
hybrid strategy that introduces steel and concrete in highly stressed load-transfer areas.
The premium for height is driven by structural realities resulting from height. The length
of gravity paths and overturning moments caused by wind and seismic loads are
inexorably amplified with height. The SOM report notes that a 30-story building will
have a 9 times greater overturning moment to contend with as compared to a 10-story

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building. Still, the report concludes that urban population growth will make tall building
construction difficult to avoid.
The other argument used to justify tall building construction is one of surface-to-volume.
The SOM report (SOM 2013, 2) references an “ability to be more energy efficient than
single family residences” because of shared floors and ceilings, and a reduced area of
weather exposed surfaces. Smith (2016) also notes the advantage reduced building
enclosure area, citing the reduction of high energy demand ground floors and roofs in a
single tall building as compared with multiple 3-story buildings. The comparisons are
suspect, especially comparing a tall building with a single-family residence. Data
suggests that, while larger buildings are potential candidates for net-zero, smaller
buildings may be easier in meeting the goal. While net-zero energy single-family
residences are not formally tracked, the New Buildings Institute reports on net-zero
commercial buildings in the U.S. (NBI 2016). Nearly 80 percent of the 53 data-verified
net-zero energy buildings as of 2016 are small, under 25,000 square feet, and a single
story, while net-zero tall buildings remain aspirational (Fortmeyer 2006; Gutierrez and
Lee 2013; Chambers 2014). A more apt comparison might be a tall building on the low
end of the CTBUH scale of approximately 35 stories or 150 meters and a supertall
building (300 meters), as discussed in Section 7.3.5.
The larger roof area ratio provided by smaller structures and counted by Smith as a
disadvantage, can also be advantageous. Most net-zero energy structures rely heavily on
roof-mounted photovoltaics to provide onsite energy generation. The geometry of the tall
building prohibits this as an effective solution, there being far too little roof area. Instead,
effective site energy generation requires the activation of the façade system. One strategy
for this is known as building-integrated photovoltaics, (BIPV). BIPV systems have been
discussed and proposed for decades, but with little in the way of application on tall
buildings, largely because of the cost and complexity they add to curtainwall system
design and delivery. Building and façade elevation orientation, shading from neighboring
buildings, aesthetic considerations, a desire for maximized vision glass area, and
available technology solutions all play a role in limiting these applications to date.
Then there is the problem of access to the TCB façade when installing, maintaining,
retrofitting or renovating the curtainwall system, yet another manifestation of the
premium for height. Jerome and Ayón (2014) claim, “A significant part of the cost of

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projects in New York City comes from the logistics of access.” Access to the façade
system, from inside, outside, or both, is a prominent part of façade retrofit planning.
Access to the façade exterior is often preferred as a renovation strategy, as it tends to
minimize disruption. Height and dense urban environments—both characteristic of tall
buildings—tend to complicate façade access from the outside. For these reasons, façade
renovation strategies center around means of access to the façade system, and minimizing
disruption to building occupants if the building remains operational as related
considerations. There can be considerable value in keeping a building operational during
renovation demolition and construction to preserve property lease revenue streams or to
prevent relocation costs, and this value can drive higher complexity and cost in façade
renovation implementation schemes. The result is the prospect of high cost and risk to the
owner of a building in need of façade upgrades. In the context of an aging building stock,
this becomes a significant barrier to the implementation of widespread façade renovations
that could provide improved energy performance and occupant comfort, and contribute to
the transformation of the built environment to a resilient and sustainable future.
Icons of (un)sustainability?
The tall building vernacular has clearly progressed in key aspects of performance since
the initial crop in the 1960s. Proponents often site recent model iconic projects,
including:
§ 30 St Mary Axe (formerly the Swiss Re Building); 2003, London, Foster and
Partners, 41 stories; claimed by Foster as London’s first ecological tall building
(Massey 2013).
§ The Shard; 2012, London, RPBW, 95 stories (72 habitable); designed around
“principles of low carbon and increased efficiency (Guthrie 2012)
§ Tower at PNC; 2015, Pittsburgh, 33 stories, Gensler, LEED Platinum certified;
designed to use 60% less energy than ASHRAE 90.1 2007, daylighting to 92%
workspaces, naturally ventilated 43% of year (Caulfield 2016).
§ Shanghai Tower; 2014, Shanghai, Gensler, 128 stories, claimed by Gensler as
the world’s greenest super high-rise; LEED Gold certification, Three-star Green
Building award, reduced energy consumption by 21 percent, carbon footprint
reduction of 37,000 metric tonnes per year, 25 percent reduction in materials,
claims 43 different sustainable technologies (Eco-Business 2016).
These buildings have all been widely celebrated in the popular press as icons of
sustainability (Barrera 2009; Guthrie 2012; Murphy 2016; Jewell 2017), but questions

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remain. Post-occupancy assessment of actual performance, however, has been rare. The
adoption of mandatory energy performance in some cities has revealed green icons,
LEED certified, as energy hogs, and some critical authors have emerged (Navarro 2012;
Roudman 2013). Massey (2013) challenges the 30 St May Axe use of carbon intense
materials, a complex façade system that has failed to function as intended, and an
unusually low ration of usable to total area, and charges that while failing to support
sustainable outcomes, the building has manifested the illusion that “design can manage
the climate risk of postindustrial production.”
Much academic research is now focused on embodied carbon (Cabeza et al. 2013). In
practice, specialized studies, like the SOM (2013) report discussed above, are beginning
to embrace the issue of embodied carbon, but the academic work is lacking
implementation in building practice (De Wolf et al. 2017). Building service life—an
effective way to mitigate embodied impacts—remains undefined or under-defined in
projects, codes, standards and rating systems. Project promotional literature, as with the
projects above, has embraced carbon savings, e.g., metric tons per year (Shanghai Tower
2015, 6), although typically focused on carbon savings resulting from operational energy
savings; embodied carbon issues are largely ignored in practice. Material selection is
slowly becoming integrated into building design practice (Basbagill et al. 2013), but there
is need of refinement in the assessment of buildings and their major assemblies (Dixit et
al. 2012). This is apparent in the double-skin façade systems that are typically adopted for
green buildings.
The four buildings referenced above all include variations of complex multi-layer skins
systems involving double and triple high performance glazings, with ventilated cavities
and automated shading systems located in the cavities, and other details that add
considerably to the material, and consequently, the embodied carbon, footprint of the
building. These green “features” are often only assessed in terms of their contribution to
operational carbon reductions. The outer skins act as cloaks to add insulation, reduce
energy consumption and enhance thermal comfort. The designs vary widely (Vaglio
2015), with the cavity between skins ranging from inches to meters, with some including
public and circulation space within the cavity (Figure 7.4). The can also accommodate
operable windows in the inner skin that are challenging and sometimes not possible in tall
building applications with conventional façade systems.

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There is a significant
monetary cost for these
systems, which is
accounted for. The energy
savings resulting from the
feature is typically used to
offset the additional cost
over time, in a payback
scenario. There is also a
cost in embodied carbon
resulting from the
additional material, but
this is often not accounted
for. This cost also can be
evaluated against
operational carbon savings
to measure the effect on
lifecycle carbon footprint,
and the effectiveness of
the design strategy. This
analysis can reveal that
these material intensive
strategies, utilizing carbon intensive materials like aluminum and glass, can take decades
to offset the embodied carbon debt with operational carbon savings, with the potential of
the payback period exceeding the service life of the building or assembly (Frey et al.
2011, Jones 2014). These designs also amplify the complexity of the façade system,
which increases recurring embodied carbon resulting from repairs, maintenance and
retrofit through the operational lifecycle of the system. Given that these façade systems
are all custom designs, and consequently at least somewhat experimental in nature, there
is also the question of the impact of system complexity on the service life of the system,
which could dramatically impact the embodied carbon debt. De Wolf et al. (2017) note
that reducing embodied carbon “…is an essential response to national and global targets
for carbon reduction.”

Figure 7.4: The cavity of the double-skin Shanghai Tower (2014,
Gensler) encompasses extensive public meeting and circulation
space (author’s photo).

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Demolition or perpetual refitting: What to do when you “can’t knock them
down.”
Weiss (2015), in discussing “old tired Midtown assets” addresses, “how you make these
buildings better when you can’t knock them down.” The economics don’t work for
demolition and building replacement (Willis 2012; Zaborski 2017). Some developers
have apparently found solutions in major building renovations that include the façade
system (section 7.5.5). Others claim that the economics of façade renovation don’t work
economically and suggest that building demolition and replacement may be the only
option (Browning et al. 2013), or that minimal repairs may be the best path forward
(Jerome and Ayón 2014). Such is the dilemma of façade retrofitting TCBs. Chapter 4 and
section 7.3 above clearly establish the inherent sustainability of building reuse as
compared to demolition. Just as the answer to how long a tall building should last is
unanswered, so is the question of what to do with them at the end of their service life
(Wood 2012). Weiss may be correct; it may not be economically viable to demolish
them. The drive is on for ever taller buildings, but the premium for height manifests here
as well; the taller a building the more challenging, risky and expensive, its demolition.
Explosive demolition is out of the question in the vast majority of cases given their
context of dense urban environments. Instead, they must be disassembled, and very few
tall buildings have been dismantled in the roughly 150 years of their construction. The
Singer Building (1906, New York City, Earnest Flagg architect, demolished 1968), a
onetime tallest building in the world, is the tallest to be demolished, at 47 stories, 612 ft
(187m). The current tallest building in the world (Burj Khalifa in Dubai), in comparison,
stands over 4-times taller at 2,722 ft (829m) with 163 floors. Of the 3,966 buildings 150m
and above built worldwide only four, or 0.1 percent, have been dismantled (Table 7.3).
Of these, only the Deutsche Bank Building was a TCB, demolished because of damage
incurred during the destruction of the World Trade Center Towers in 2001. The
deconstruction took years and cost at least $164 million (Varchaver 2008). Other
methods are being experimented with (Economist 2014).
The demolition process (NYT n.d.) was essentially construction in reverse—a top-down
procedure—with the added complexities like the breaking up of concrete floor slabs and
management of toxic materials like asbestos. In addition, the entire building was encased
in scaffolding to provide a buffer zone to prevent damage and injury from falling
materials, yet there were still accidents and injuries, highlighting the risk associated with

297
the process. Starting from the top, façade materials were removed and pulled inside the
building and transported by crane or construction life to the ground, where trucks
transported the material for disposal or recycling. The structural steel followed. Then the
floor slab was broken up, and the process began again on the next floor. Just as TCB
renovations must be considered on a case-by-case basis, so must their deconstruction.
Note that no building with a composite (steel reinforced concrete) structural system has
yet been taken down. It is likely that this kind of structural system will prove significantly
more challenging to dismantle that a steel structure. Japanese construction giant Kajima
has developed an alternative bottom-up deconstruction process involving supporting the
building on massive computer-controlled hydraulic jacks, removing the ground-level
floor, and lowering the entire building to create a new ground floor, repeating the process
through each floor (Kajima 2017). Kajima claims advantages of safety and noise
abatement.
The very act of building thousands of new tall, supertall and megatall buildings in dense
urban environments, without any forethought to their service life planning or how the end
of their service life will be managed, is an inherently unsustainable practice. The
demolition aspect of this dilemma is diminished, however, if the buildings last forever.
Wood (2012) claims, “[tall buildings] need to be designed to be never taken down, such
that their life cycle is as close to forever as you can get.” Willis (2012) agrees, “…you
don’t take skyscrapers down, you refit or repurpose them.” The problem was, and
continues to be, that tall buildings were not and are not designed in this context, and lack
the adaptive capacity to accommodate change in function and use, the need for
maintenance, future upgrades and renovation, and other conditions that will emerge over
a service life of “forever.” Adaptive capacity like that of the Blue Cross-Blue Shield
Tower (1997, Chicago, Goettsch Partners, Lohan Associates), which, a decade after
original completion, accommodated a 24-story addition atop its original 33 floors
(CTBUH 2012). Or the Tour First in Paris, France’s tallest building, a 1970s tower that
Table 7.3: Deconstructed buildings 150 meters and over worldwide (CTBUH 2017).
Name City Height(m) Height(ft) Floors Built Demo Material
Singer Building New York City 186.6 612 47 1908 1968 Steel
Morrison Hotel Chicago 160.3 526 45 1925 1965 Steel
Deutsche Bank New York City 157.6 517 39 1974 2011 Steel
One Meridian Plaza Philadelphia 150 492 38 1972 1999 Steel

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was built up an additional 216 feet (66m) in a 2007 refurbishment (CTBUH 2017b). Or a
façade cassette system as discussed in section 4.4.8, that would facilitate the retrofitting
of new high-performance glazing products. Anticipating the forces of change and
obsolescence would change the design of buildings and their façade systems in ways that
could significantly enhance the sustainability of buildings and urban habitat.
High enough: The MURB cluster as an alternate density model
Progress is being made with tall building efficiency, including tall buildings built to
Passive House standards, the latest and largest being the 26-story residential high-rise at
Cornell Tech on New York City’s Roosevelt Island (2017, Handel Architects). It is
notable, however, that the discussion remains tightly focused on operational energy
consumption; the issue of embodied carbon or building service life rarely comes up, even
with LEED Platinum certified buildings, except with singular voices like Sturgis (2017;
2017a). The embodied carbon problem presented by tall buildings is significant, and
ultimately perhaps the greatest barrier to sustainability for this building form. Increasing
height will makes the problem progressively worse. There may well be other ways to
think about density beyond urban environments with supertall buildings packed shoulder
to shoulder. The MURB building form discussed in Section 7.3.3 seems worthy of
consideration. The story heights are potentially within the reach of mass timber structural
systems, with the potential for significant embodied carbon reductions. The lighter
weight, moderate gravity path and broader base of these structures would minimize the
problematic overturning moment and accommodate lighter foundations, adding to the
embodied carbon savings. The concentration of towers surrounded by open space, Uno
Prii’s vision of tower-in-the-park, has clear advantages in resilience and adaptability.
Like other aspects of mid-century Modernist experimentation, aspects of the tower-in-
the-park were flawed, or became at some point obsolete, but at the same time are
evidencing high adaptive capacity that greatly facilitates their rehabilitation. The open
green spaces intended to enrich the inhabitants were underused and neglected, but now
are providing rich opportunities as infill spaces in new planned communities (Urban
Toronto 2017). Linking planned communities of MURBs with high speed rail links to the
city center may provide a more sustainable alternative to the replacement of older tall
buildings with new supertall and megatall construction. In the case of the latter,
sustainable practice would integrate adaptive capacity as a key consideration in current
and future planning exercises, addressing the questions around what happens to these
structures and their urban habitat 20, 50, 100 to 500 and 1000 years from now.

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7.4 Façade system renovation considerations of TCBs
It is established that vintage TCBs present a particular rehabilitation challenge. The
following identifies and discusses the particular considerations of façade system
renovation.
Curtainwall systems through the 1960s and into the 1970s can be regarded as
fundamentally experimental given the sudden widespread application of a building
technology largely without precedent (Kelley 1996, 18; Wigginton 1996, 3.94-3.96;
Prudon 2008, 30; Jerome 2011, 152; Ayón and Rappaport 2014, 18). Consequently, there
is no simple rule set for building evaluation or renovation strategy in this respect, but a
general acknowledgement that each application must be considered on a case-by-case
basis (Timberlake 2015; Jerome 2014; Prudon 2008, 121). A review of relevant
considerations when evaluating curtainwall systems for possible intervention suggests the
challenges of this undertaking, as summarized in Table 7.4.

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Table 7.4: Summary table of considerations for condition assessment and case evaluation of
feasibility and strategy in the facade intervention of mid-century TCBs.
1. case variations
Variations in system design, material, detailing and execution prevent
convergence of retrofit best practices. Condition evaluation complex, costly.
2. service quality
Seasonal condensation and moisture infiltration has frequently compromised
service quality of curtainwall. Anchors and embeds may be effected.
3. structural capacity
Codes and design loads now more stringent. Double glazing upgrade may require
structural modifications. Anchors and embeds may be inadequate.
4. energy & carbon
Single-glazing, thermally unbroken framing, inadequate insulation, and high air
infiltration characterize these early curtainwall systems.
5. health & comfort
Same factors compromised thermal, acoustical, and visual comfort, factors
increasingly linked to health and productivity.
6. life safety
Older window systems and spandrel panels may be increasingly prone to
disengagement and falling under escalating storm frequency and strength.
7. code creep
In addition to structural, code changes in fire, safety requirements, energy
conservation, and others, may drive the facade renovation program.
8. marketability
Low floor-to-floor heights and deep floor plates combined with indistinctive
repetitive facade may challenge renovation upgrade to Class-A designation.
9. renovation goals
Often conflicting goals of cost, preservation, modernization, energy efficiency,
sustainability, resilience, and comfort must be balanced and aligned.
10. cost & disruption
Cost and disruption to ongoing building ops are greatest barriers to curtainwall
renovation. Few owners can afford to vacate occupants during renovation.
11. means & methods
Installation strategy drives program if building is to remain occupied; key to
mitigating disruption to ongoing building ops during demo & construction.
12. tall & urban
Site congestion, material handling, and work area access amplify the complexity
and importance of installation strategy.
13. reuse over recycling
Extreme interventions like facade replacement burden the solid waste stream.
Analyze embodied impacts of intervention strategy. Prioritize reuse, recycle rest.
14. heritage & preservation
The cultural value of this unique midcentury building type adds another dimension
to the consideration of curtainwall renovation.
15. climate change
Changing climate conditions driven by anthropogenic carbon emissions bring high
level uncertainty to future service environments of buildings and façade systems.

1. Case variations: The early curtainwall buildings were essentially experiments in
building form and technology, and consequently involved wide variations in
design, detailing, use of materials, fabrication processes, and means-and-methods
of their installation. The supply infrastructure for this emerging technology was
formative, resulting in further variations in build quality with respect to
fabrication, assembly and installation. These variations necessitate evaluation on a
case-by-case basis, often involving expensive probes of the building façade to
facilitate inspection of concealed areas. Combined with other considerations of

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building occupancy and use, these factors have served to render convergence of
façade renovation strategies elusive. As a result, other than field testing standards
such as ASTM E1105 - 15, there are industry standards prescribing best practices
to guide retrofits of aging curtain wall assemblies.
2. Service quality: Air and water leakage must be rigorously assessed and
ultimately corrected (Jerome and Ayón 2014, 18). The durability of materials,
components, and systems impacts service quality and ultimately becomes a
determining factor for a building system’s service life. Seasonal condensation and
moisture infiltration has become a problem with many of these early façade
systems. Earlier examples of this building type sometimes included mild steel
frames and anchors, as was the case with Lever House; this proved to be the weak
link in the curtainwall system, leading to its replacement in 2001 (Hart, 2003).
The UN Secretariat façade had begun to deteriorate after only a few years of
completion (Ayón and Rappaport, 19).
3. Structural capacity: This is often a dominant consideration when evaluating a
historic building for major renovation, and the early tall curtainwall buildings can
be problematic in this respect. For instance, in New York City the early tall
products of this building type were designed under the city’s 1938 building code
prescribing wind pressure of a mere 20 pounds per square foot (NYC Buildings
ND, Section C26-350), with no specification for suction loads (the relevant codes
were substantially revised in 1968). This is a particular concern with respect to the
escalation in frequency and strength of major storm events resulting from climate
change. In some cases, the existing structures require expensive structural
upgrades just to accommodate the added dead load of replacing single-glazing
with double-glazing (Browning et al. 2013, 5). Structural integrity of existing
façade assemblies and components must be evaluated, including anchorage
systems.
4. Energy & carbon: The façade systems of the earliest of this building type were
not designed to optimize energy-conservation and have never been good
performers. Constructed of thin thermally unbroken framing systems with single
glazing and under-insulated spandrel panels, they are prone to high energy losses
through the metal and glass enclosures. High air infiltration rates are also
characteristic.
5. Health & comfort: Single-glazing, large areas of vision glass, and high air
infiltration rates resulted in interior environments with compromised thermal,
acoustical, and visual comfort. Air infiltration was a common problem with many
of the early curtainwalls, a performance factor that tends to deteriorate over time
as weather seals age. A growing body of evidence links performance factors like

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air infiltration and thermal behavior to comfort, health and productivity of
building occupants (Wargocki 1999, 175-77; Roelofsen 2002, 260).
6. Life safety: Public safety features including aged fire-separation and smoke
control systems must be assessed and corrected. Objects falling from tall urban
buildings are obvious life safety threats. Older curtainwalls may be at risk. Cover
plates can detach, pieces can fall, even entire wall sections can fail (Kazmierczak
and Hershfi 2010, 12, 17; McCowan and Kivela 2011, 19; Jerome and Ayón
2014, 15). An iconic TCB in Chicago (2012, confidential interview, names
withheld on request) had a large piece of glass fall from the façade during a high
wind event, resulting in a fatality. The original windows comprising the vision
glass areas of many early curtainwalls included operable vents. Single-glazed
awnings, hoppers and horizontally pivoted vents were common choices. These
window vents included standard hardware sets available at the time, which had
not been designed to perform under the high suction and positive lateral loads to
which these buildings are subject. As a result, the original windows often failed to
retain the sashes in the open or closed positions, or even worse, the sashes
disengaged and were blown away or fell off (Ayón and Rappaport, 19). Over the
years, most operable units were seal-shot with ferrous anchors that are now
corroded due to exposure to condensate and galvanic action. Spandrel metal
panels have also been found to be poorly secured or loose at some buildings
(Jerome and Ayón, 15). In the absence of immediate corrective actions, the
potential for window sashes or metal spandrel panels to separate and fall from the
building during one of the extreme meteorological events resulting from climate
change is a serious safety concern that worries building owners, insurers,
practitioners and public officials.
7. Code creep: Changes to the structural code requirements since the inception of
these early curtainwall buildings, raising potential life-safety issues, were
discussed above but there have also been changes to fire codes, safety
requirements for glazing, energy conservation, environmental performance, and
more. The trend of evermore demanding code constraints is expected to continue.
Renovations are required to meet current code stipulations, which may drive the
renovation program.
8. Marketability: Some of the vernacular manifestations of this building type are
encumbered by design shortcomings including low floor-to-floor spans, repetitive
and indistinctive facade design, and deep floor plates that severely restrict
opportunities for daylighting and view. These present challenges to renovation
upgrades to Class-A building designation, and the pursuit of higher lease rates
that accompany this classification. Some building professionals and developers

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regard these as inherent limitations, claiming that demolition and new
construction are the only viable economic solution (Browning 2013, 6).
9. Renovation goals: The desire for improved energy efficiency and enhanced
thermal and acoustical comfort are potentially in conflict with preservation goals,
which are typically focused on retaining the original façade fabric. Preservation of
the original appearance and materials is often in conflict with a building owner’s
notion of “modernization” as a means to increase a building’s market value
(Weiss, 2015). Then again, these considerations can conflict with the project
budget and financial goals.
10. Cost & disruption: Ultimately, the greatest barrier to needed façade renovation is
cost, and even more so, the disruption to ongoing building operations with its own
cost and liabilities that can exceed those of the façade removal and replacement.
Intrusive intervention programs like façade replacement require elaborate
implementation strategies aimed at mitigating this disruption. Not many building
owners can afford to completely shut down a building for two years or longer—as
was done with the UN Secretariat building (Adlerstein, 2015)—while renovation
programs are implemented. Another example is 330 Madison Avenue in New
York City, where the building owner spent $100 million to reconfigure and
renovate the original building lobby, replace all the building systems, and re-clad
the facade to reposition the building within the competitive real estate
marketplace for Class A office buildings in Midtown Manhattan. This overhaul
resulted in a very different and contemporary appearance that allowed the owner
to increase rents by 25% (Weiss, 2015). These are unique cases and are not
representative of the budgets, goals and ambitions of owners of many similar
buildings for whom the loss of lease revenues or cost of relocating tenants or
employees during construction is far too expensive.
11. Means & methods: Most buildings will have to remain operational throughout
the construction process of a façade renovation program. The result is that
installation strategy, with a focus on mitigating disruption to ongoing building
operations, becomes the predominant driver in the renovation process, in some
instances representing a higher priority than cost; an owner is willing to spend
more to reduce the risk that accompanies the potential disruption to building
tenants. Yet elaborate and costly methods involving the construction of temporary
barriers, providing work area access from outside the building, and swing
schedules involving temporary relocation of partial building areas, are at best only
moderately successful in mitigating occupant exposure to the noise, dust and
debris of façade removal and replacement.
12. Tall & urban: Most of these considerations are relevant to any façade renovation
project, but their effects are amplified by tallness—the bulk and height of the

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existing building. The taller the building the stronger the wind loads, the more
challenging it becomes to access the façade surface for purposes of assessment or
renovation work, and the more difficult and costly become renovation programs
simply in terms of material handling, workforce access, operational logistics, and
construction means-and-methods). These effects are further exacerbated by the
typical location of this building type amidst dense and congested urban habitat,
complicating material deliveries, onsite storage, staging areas for installation
activities, and labor access to the site.
13. Recycle & reuse: Construction and demolition (C&D) debris is the waste
material produced through construction processes, including new building
construction, renovation, and demolition. C&D debris is a consideration because
of the enormous volume entering the solid waste stream, a significant percentage
of which ends up in landfills. As a byproduct of what Moe (2010, loc 120) refers
to as “an orgy of demolition and reconstruction,” the U.S. Department of
Transportation (U.S. DoT ND) estimated 448 million tons of C&D debris
produced nationally in 2012, representing one of the largest components of the
solid waste stream (approximately 23%). Approximately 70% of this is presumed
to have been recycled, which still resulted in 80 million tons landfilled. A subtlety
of these statistics, however, is that about 80% of the total C&D waste is bulk
aggregate (concrete) and reclaimed asphalt pavement with high recycling rates
(85-99%). The remaining 20% of the total C&D waste has a much lower
recycling rate (35%). This would include any C&D generated from façade
renovation. Data at the grain of the façade system is not tracked, but in the case of
curtainwall replacement, two materials predominate; metal and glass. The metal,
most often aluminum, has a high recovery rate because of its scrap value. Glass
on the other hand is not recycled, and is either down-cycled or landfilled, e.g., the
glass for the Javits Convention Center curtainwall replacement (Section 7.5.6)
was landfilled. Recycling practices have gradually improved, but contrary to the
perception of many, they are no panacea even in the in the best of circumstances.
C&D waste, including any recycling, produces an embodied impact that is seldom
considered in a building renovation assessment (Patterson et al. 2014). Clearly,
reuse is preferable in all respects to recycling (Moe 2010, loc 120; Carroon 2010,
loc 271). Buildings and building systems should be designed to maximize service
life and the potential for reuse, and minimize the need for recycling.
14. Heritage & preservation: Clearly, the renovation of tall curtainwall buildings
represents a challenge in the best of circumstances; yet, when heritage value and
potential preservation are considered, the complexity of the challenge is greatly
amplified. With a focus on protecting historic appearance, materiality, and
authenticity while developing renovation strategy, the preservationist’s

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perspective brings yet another layer of complexity to the façade retrofit dilemma,
adding a new set of potential constraints and considerations to an already daunting
process. With relatively little in the way of studies about renovating this building
type, it is far from clear what constitutes best practices in the context of balancing
the often-competing objectives of preservation, sustainability and redevelopment.
15. Climate change: Last, but far from least, accelerating changes to earth’s climate
infuses building design practices with uncertainty. Buildings should have long
service lives, which exacerbates the challenge of anticipating what the future
service environment may be decades from now. Buildings must now be designed
on the basis of projected data rather than historical data, as has been past practice;
emerging conditions are already unprecedented. The following considerations are
adapted from Gething (2015, 51):
§ minimum code requirements: consider adoption of augmented standards
§ wind: increased deflections.
§ extreme wind: airtightness and detailing of air and vapor seals; airborne
debris impacts.
§ fixings: increased loads and deflections, consider over-sizing.
§ detailing: strategies to accommodate exposure rating increases.
§ materials: effects of extreme and extended wetting, drying, and UV exposure,
including shrinkage, expansion, softening, hardening, absorption, rotting.
§ extreme temperatures and humidity: adequacy of thermal breaks, variations
in and range of condensation resistance of assemblies.
Note how the considerations discussed above are intertwined; e.g., service quality
directly influences energy efficiency and comfort. The complexity of these interwoven
factors demands holistic analysis when developing renovation strategy, and a highly
collaborative multidisciplinary process to appropriately balance the many relevant
considerations.
7.5 Façade retrofit types
The conceptual typology represented in this section was developed over time, eventually
tested in two surveys, and ultimately used as the classification in the facaderetrofit.org
database, as described in section 2.6.3. Richards (2015) defines similar typologies. Other

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researchers have discussed reclad and overclad, establishing them as fundamental façade
renovation strategies.
Unlike automobiles and other consumer products, buildings are inherently bespoke
creations. With tall buildings and large commercial structures this made-to-order
character extends to the façade systems, and façade designs for such buildings are equally
bespoke. While common façade system types include precast curtainwall and masonry
with punched windows, and the discussion following may apply to these systems, the
primary focus here is metal-framed curtainwall systems in TCB applications.
7.5.1 Proposed TCB façade renovation typology
[Earlier versions of this scheme were published in Patterson and Vaglio (2011).]
The reclad and overclad retrofit strategies involve contemporary modular, prefabricated,
aluminum-framed curtainwall systems. The façade renovation typology is represented in
Figure 7.5, diagraming the broad categories of retrofit types, although the many possible
variations within each type ultimately render each façade renovation a unique
undertaking. Illustrations follow in Figures 7.6 – 7.10.

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Renovation and restoration are essentially the same activity, but with different goals.
• A renovation is any program of facade system improvement.
• A restoration program includes returning the facade system to its original state, with a priority
emphasis on appearance.
A renovation or restoration can be either a refit or retrofit.
• The goal of a refit is to return the performance of the facade system to something close to its
original state.
• A retrofit uses new technology (materials/products/systems) to enhance performance beyond the
original facade system design.
Selective replacement and enhancement (SER) are partial renovations.
• Selective enhancements - add interior glass ply, add insulation, add shade screens, fins or louvers,
etc.
• Selective replacement - windows, spandrel panels, shadow boxes, vision glass, insulated panels,
etc.
Overclads and reclads are major renovations.
• An overclad is the application of an additional layer outboard of the existing façade.
• A reclad is the complete removal of the existing façade and replacement with a new system.
Figure 7.5: Façade renovation typology (Adapted from Martinez et al. [2015]).

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description: additive strategies to improve
appearance or performance, e.g., finish and seal
repair, insulation in spandrel areas, interior/exterior
shading systems, addition of interior glass ply to
improve solar/thermal performance, etc.
application: best where the original system is in
good condition with significant remaining predicted
service life, but performance or appearance are
wanting and can be upgraded with relative ease at
reasonable cost.
pros
• disruption can be minimal
• may provide improvements at lesser cost than
reclad or overclad strategies
cons
• limited aesthetic/performance options
• appearance/performance gains must offset
embodied energy and financial costs

Figure 7.6: Façade renovation type: selective enhancement.

description: replacement of select façade
components, e.g. the replacement of vision glass
infill panels in a metal framed curtainwall system
application: best where a component of the façade
system has prematurely failed or become obsolete,
and can be replaced with relative ease.
pros
• minimal system intervention
• minimized material requirements
• shorter construction duration
• lower cost/quicker payback
• less disruption
• performance enhancements; e.g., replacing single
glazing or old IGUs with high performance glazing
• work can be scheduled for after working hours
cons
• inadequate to many façade renovation needs
• may not provide adequate performance
enhancements
• limited aesthetic options and impacts
• unlikely to achieve optimized system performance
• cost may exceed total façade replacement

comment: difficulty of removing vision glass from
original system, especially newer structurally glazed
unitized systems, may make retrofit glazing
impractical.
Figure 7.7: Façade renovation type: selective replacement.
Selective Replacement Selective Enhancement

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description: the application of another layer,
typically outboard, to the existing façade system,
e.g., the addition of a new curtainwall system to a
building exterior complete with vision and spandrel
glass, remove old vision glass from inside and flash
old system to new to finish.
application: a frequent application of this strategy
involves overcladding early stick built CW systems,
using the original vertical primary structural mullions
as primary support for a new unitized CW system.
pros
• extends use of existing façade components
• can provide new system performance
• broad range of aesthetic options
• generally less disruptive than reclad; minimizing
access from inside is possible
• may be more material/cost efficient than total
façade replacement (reclad); less embodied
carbon intensive
• may benefit from thermal buffer provided by
additional skin
• minimizes C+D waste
cons
• requires extending the outer boundary of the
façade system
• feasibility, complexity, and cost dependent upon
existing façade system type and condition
• typically requires replacement of original vision
glass for appearance/performance reasons
• more aesthetic constraints than total façade
replacement (reclad)
Figure 7.8: Façade renovation type: overclad.

description: demolish existing system and replace
with new
application: best where existing system is
significantly below quality standards, selective
enhancements are impractical, and disruption
impacts can be mitigated.
pros
• can provide state of the art new system
performance
• maximum aesthetic options
• may ultimately be more cost effective than a
reuse/refit strategy
cons
• costly and most disruptive: cost driven by
dislocation of occupants, or mitigating disruption to
ongoing building operations
• material intensive; no reuse of existing materials,
high embodied carbon
• C+D waste
comment: maximum embodied carbon impacts;
typically, all but a percentage of aluminum ends up in
landfill.
Figure 7.9: Façade renovation type: reclad.
Overclad Reclad

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description: adds new outboard skin as with
overclad, but utilizes the resulting cavity as an
integral aspect of façade performance
application: best where comfort and acoustical
performance are dominant goals over first cost
considerations
pros
• extends use of existing façade components
• supports minimal disruption strategies
• cavity can provide protected space for dynamic
shading devices
• improved options for acoustical performance
• improved options for natural ventilation
cons
• requires extending the outer boundary of the
façade system
• additional loads to structure and CW anchorage
• additional maintenance requirements
• additional material and embodied carbon

comment: high potential in the right application, but
an inflexible strategy with respect to accommodating
existing conditions.

Figure 7.10: Façade renovation type: double-skin overclad.

7.5.2 Renovation and restoration
Façade interventions can be differentiated by the goals that comprise the construction
program, into the broad categories of renovations or restorations. Both can share aesthetic
and performance upgrade goals, but restorations include aesthetic constraints with the
intent of closely replicating the appearance of the original façade. Either renovations or
restorations can be further characterized as refits or retrofits, again largely as a matter of
intent, with refits comprised of repairs and retrofits of upgrades.
7.5.3 Refit and retrofit
A façade refit is an intervention with the primary objective of returning a degraded façade
system to some prior level of performance, essentially a repair strategy.
Façade retrofit involves the use of technically or aesthetically superior materials or
products as replacements for existing façade elements, often with the goal of upgrading
or modernizing the building image. Retrofits may also include performance
enhancements that exceed performance attributes of the original façade system design. A
Double-skin Overclad

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restoration retrofit will constrain the use of superior materials to those that closely
replicate the original appearance, even at the expense of performance.
Façade refits and retrofits can be part of a planned façade maintenance program, or a
remedial response to an unanticipated or premature failure of a façade material or
component. Both add to a building’s lifecycle carbon footprint in the form of recurring
embodied carbon. As part of a maintenance program, planned cycles of partial
renovations in the form of refits or retrofits hold potential as strategies to extend service
life, thereby reducing the lifecycle embodied carbon footprint of the façade system
(4.4.8).
7.5.4 Selective enhancement and replacement (SER)
Façade refits and retrofits are variations of a strategy of façade retention, where the
original façade is kept in service. Selective replacement may include such façade
components as vision glass, spandrel panels, shadow boxes, insulated panels, and mullion
caps. Selective enhancements often include refit activities ranging from the repair of
seals, the refurbishment of individual façade components and the renewal of material
finishes, along with retrofit activities intended to improve performance, like the addition
of an interior glass ply over a vision window, installation of additional insulation,
installation of interior blinds, or the exterior installation of shade screens, fins or louvers.
Many renovation programs can include both enhancement and replacement. SER
strategies have the following advantages:
§ Low cost: potentially an order of magnitude difference; tens of thousands instead
of tens of millions of dollars.
§ Rapid implementation: renovation program is far more easily initiated, managed
and executed than overclads or reclads; months duration rather than 1-2 years.
§ Minimal disruption: disruption to ongoing building operations is typically far
less than overclads or reclads.
§ Low embodied carbon: minimal use of materials, and especially those with high
energy intensity.
§ Minimally invasive: retention of original fabric and appearance.

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There are also significant limitations with SER strategies:
§ Performance: limitations to performance improvements, like thermally broken
framing, and possibly, high performance glazing products.
§ Appearance: if a visual rebranding of the building is a renovation program goal,
overclad or reclad is a better strategy.
§ Warranty: warranty coverage for the new work may be unavailable or limited as
compared with overclad and reclad strategies.
An SER strategy can potentially be the most sustainable approach to façade renovation,
in spite of the limitation to thermal improvement (sections 4.2.1; 4.3.3).

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60 Broad Street
Jerome and Ayón (2014, 13-9) pose the
question, “Can the 1960s Single-Glazed
Curtain Wall Be Saved?” They then
proceed to document the in situ
conservation of a vintage TCB with a
single-glazed curtainwall. Unlike some of
the cases discussed following, 60 Broad
Street (Figure 7.11) is not an icon of
Modern architecture, but rather represents
the vernacular of the vintage TCB stock; a
Docomomo Tristate study of 200 1960s
era Midtown Manhattan buildings found
nearly 60 designed by this same architect
(Rappaport and Sigge 2004, 114). As
noted in Section 7.3.2, these structures
were designed to the 1938 New York City
Building Code, with a mere 20psf wind
pressure for structures over 100 feet, with
no requirement for the consideration of
suction loads.
The façade system for 60 Broad Street
had clearly dropped below an acceptable
service quality, plagued by air and water
leaks (Figure 7.12). In some ways, an
early client decision to reclad a structure
is easier; the mere consideration of an
SER strategy requires rigorous evaluation
of existing conditions. WASA/Studio A was commissioned for this process and began a
comprehensive assessment of the façade system that involved floor-by-floor surveys and
multiple probes. An extensive list of issues was developed that ranged from flaws in the

Figure 7.11: Original façade (author’s photo).
60 Broad Street
New York City
built: 1962
architect: Emery Roth & Sons
steel structure; 39 stories; 10’-5” floor spans
original façade: single-glazed stick curtainwall

façade renovation: 2014
architect: WASA/Studio A
structural engineer: Severud Associates
façade contractor: C&D Restoration
retrofit type: Selective enhancement/replacement
description: replacement of weathered components,
replacement of sealants and other discrete repairs.

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original façade design to rusting and galvanic action in some façade components to
structural issues (Figure 7.14).
Jerome and Ayón (2014, 16) note a
common dilemma of TCB façade retrofit.
A major cost component is access to the
façade area, a combination of many
factors, but exacerbated by tall buildings
in dense urban environments (Figure
7.13). The cost of access is essentially the
same for a minimal SER intervention as it
is for a complete reclad, which begins to
favor an overclad or reclad as a higher
value solution, which in turn can cause
consideration of building replacement.
WASA/Studio A proposed an
“incremental-replacement” option, using
the existing curtainwall structure (anchors
and frame), which had been evaluated as
structurally sound. The upgrades would
include new double-glazing, insulated
aluminum column covers and spandrel
panels, phased separately to minimize
disruption to ongoing building operations.
Original finishes (mill-finish extrusions)
and sightlines were to be preserved. With
an estimated 8-fold cost increase for the
incremental replacement option, the owner
elected to forego a more energy efficient
skin in favor of a minimal SER strategy
focused on the repairs necessary to replace
rusted and corroded components and
mitigate air and water infiltration,
estimated at $2.5 million.

Figure 7.12: Horizontal band of operable windows
were fixed shut (author’s photo).

Figure 7.13: Façade is inspected from suspended
rig in upper right (courtesy of WASA).

Figure 7.14: Extensive water infiltration through
the curtainwall had caused corrosion and rusting
of components (courtesy of WASA).

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As part of the program, an onsite prototype involving nine two-story bays was installed
on a vacant floor. The prototype included various repair strategies and was water tested in
excess of ASTM E1105 requirements, helpfully revealing deficiencies in the original
curtainwall water management capability. The final repairs included fixing and sealing of
loose spandrel panels, replacement of silicone tape and wet seals, and the repair and
localized replacement of flashing at interfaces. The goal of the SER was to enhance the
service quality of the existing single-glazed curtain wall through “discreet” interventions,
and to prolong its service life by 20 years. Jerome and Ayón (2014, 17) stress that the
service life of the repairs can be further extended through a planned maintenance
program.
Jerome and Ayón point out that the renovation strategy used on 60 Broad Street may be
ideal from the standpoint of conservation, but less so with respect to energy efficiency.
Enhancements to thermal comfort, daylighting, and other façade optimization strategies
are also limited. Yet the service quality of the façade system has been improved to the
building owner’s satisfaction, at roughly a tenth of the cost of a reclad, providing,
roughly, a 5-year return on investment. A major advantage of this minimal “discreet
repair” SER approach is the mitigation of potential embodied carbon impacts as
characteristic of overclad, and especially, reclad strategies. This is especially relevant in
the context of the time value of carbon (section 4.2.1). The authors recommend
consideration of similar strategies on similar building types, but emphasize that
appropriateness must be evaluated on a case-by-case basis.

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Façade overclads and reclads typically comprise more extensive renovations of the
façade system. The relative advantages and disadvantages of overclad and reclad façade
renovations strategies are summarized in Figure 7.8 and Figure 7.9, and discussed in the
following sections.
7.5.5 Overclad
Curtainwall overclads are a subset of a larger glass of building façade rehabilitation
strategy that includes opaque, panelized rainscreen and face-sealed systems as discussed
in Lawson et al. (1998). Overclads of TCBs involve the application of a new façade
system over the top of the existing, adding a new layer to the building skin (Figure 7.8).
This typically involves a fundamental alteration in appearance, making this renovation
strategy unsuited for façade restoration. That no instance of a restoration project
employing an overclad strategy has been identified in the facaderetrofit.org database is
evidence of the inherent conflict between this strategy and restoration goals. On the other
hand, an overclad strategy does provide opportunity for aesthetic reinvention.
An overclad strategy may provide certain benefits as compared to the reclad strategy
described in the next section (derived from Richards (2015):
§ Less disruption: An overclad strategy may allow the original façade system to
remain in place throughout the construction process. Installing the overclad
system from the outside can mitigate disruption to ongoing building operations,
and eliminate the need to even temporarily relocate occupants. Glass replacement
and finishing can parallel the framing system installation, or can follow the
exterior metal framing installation. In office building retrofits, this can be done
from inside after normal working hours.
§ Fewer materials: An overclad design may accommodate some level of reuse;
making efficient use of the existing façade may result in fewer materials than a
reclad, accompanied by lower embodied carbon impacts. If original façade is
single glazed, consider reusing, with the addition of an additional single or
double-glazed outer skin.
§ Less waste: Some part of the original façade is generally retained with an
overclad strategy, potentially preventing more materials from entering recycling,
down-cycling, or solid waste material flows. Removing unnecessary aluminum
materials in the existing works for recycling is advantageous.
§ Higher performance: Reusing the existing façade opens up possibilities for
enhanced thermal and acoustical insulation. Managing cavity dynamics and

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integrating façade and building functions may facilitate natural ventilation
strategies, daylighting, and glare control. A consideration is that these strategies
may increase façade complexity and maintenance. The early design participation
of appropriate consultants, material suppliers, and fabricators is critical to success,
as is commissioning to assure quality installation and proper operation.
§ Lower cost: If the disruption to ongoing building operations and occupancy can
be minimized, and more efficient material options are realized, an overclad
strategy has the potential to be more economical than a reclad.
In application, overclads are often excluded as a viable option for one or more of the
following reasons:
§ Code limitations: An overclad pushes the existing building envelope outward,
which may clash with surrounding buildings or objects, or violate building code
requirements; existing building envelopes are often designed to the outer limit of
setback regulations. New York City adopted the Zone Green Text Amendment
(NYC 2012) that allows the façade to be pushed out 8-inches to accommodate
insulation upgrades to existing buildings. This allowance can potentially
accommodate an overclad system. Zone Green also allows for awnings and
shading devices over vision glass extending out 30-inches from the façade.
§ Structural considerations: An overclad typically involves the addition of
material to the building skin that can increase the dead load of the building,
possibly beyond the capacity of the building structure. Some of the vintage TCB
structural systems have proven incapable of handling an upgrade from single to
double-glazing (Browning et al. 2013). Changes in building codes over the years
have resulted in higher design wind loads that may have to be accounted for in the
renovation. An incremental increase in the building profile resulting from the
overclad will increase the area transferring wind loads to the building structure,
resulting in some local increase in wind loads. A deeper overclad system with
glass offset further from the building structure can result in higher moment forces
in the structure. These factors can potentially combine to necessitate costly
structural upgrades that can be impractical or economically unfeasible. Also,
compromised or under-designed anchorages of the existing system could require
major structural retrofit that may begin to favor a more invasive reclad strategy, or
conversely, a lesser selective repair and replacement strategy.
§ Aesthetic considerations: An overclad will alter the appearance of a building,
making this an unlikely strategy for application on a heritage building, or any
building where there is strong motivation to conserve the original facade
aesthetic.

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§ Maintenance: Depending upon the design, the cavity area may represent a
maintenance concern for the facilities management team. Maintenance
considerations are predominant drivers in the design of double-skin facades.
The overclad strategy suggests a corollary, the underclad, which is not included as a
discrete strategy here because an application has yet to be identified. An underclad can be
thought of as a window wall inset from the curtainwall, again creating a cavity as with
the overclad. The adverse consequence of an underclad is the reduction in leasable floor
area, which to most building owner-developers would be an unacceptable outcome of the
renovation process. However, it could prove a viable option for owner-occupiers that are
not looking to maximize lease revenues.
Curtainwall systems can also be applied outside of the TCB stock. Two case studies
follow, the first an overclad of a TCB, the second the overclad of a tall masonry building
with a new curtainwall system, essentially converting the building to a TCB.
Richards (2015) notes the rarity of overclad schemes in the commercial office sector, but
this is perhaps changing, at least with respect to the vintage stock of TCBs, some of
which lend themselves readily to this strategy. Such is the case with 330 Madison, by all
measures a successful overclad façade retrofit.

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330 Madison Avenue
Metals in Construction (2016, 35) reports
that property developer and owner of the
TCB at 330 Madison Avenue (Figure
7.15) wanted to improve market appeal of
this property with a modernized
appearance, increased daylight, and
enhanced comfort near the façade to
increase occupancy and lease rates. Glen
Weiss (2015), Executive VP & Director of
Leasing for property owner Vornado,
leads an in-house team that deals with
improving their stock of “old tired
Midtown assets.” His team gets involved
with, “how you make these buildings
better when you can’t knock them down,”
(sounding rather like they have a
preference demolition). Mike Zaborski
(2017) with architect MdeAS explains that
the economics just don’t work for
demolition and building replacement.
They have been redeveloping these assets
at the rate of 1 or 2 a year for the past 5 or
6 years, the process requiring 3-4 years
each from concept to lease. The process
typically includes the lobby area, major
building systems and the curtainwall
system. Their redevelopment process
requires that the building remain
operational throughout the process, which
becomes a driving consideration of the
program. The original curtainwall on 330
Madison was a single-glazed stick system
with vertical mullions as the primary

Figure 7.15: Original facade before overclad
(Courtesy of MdeAS Architects).
330 Madison Avenue
New York City
built: 1963
architect: Kahn & Jacobs
steel structure; 39 stories; 11’-6” floor spans
original curtainwall: single-glazed mullion and panel

façade renovation: 2012
LEED EB Gold; Energy Star label
developer: Vornado Realty Trust
architect: Moed de Armas & Shannon
façade consultant: Gilsanz Murray Steficek (GMS)
façade contractor: W&W Glass
curtainwall system supplier: Sotawall
retrofit type: unitized aluminum overclad
description: part of a $100m plus redevelopment,
original single glazed aluminum curtainwall
upgraded with new unitized overclad system.
Structural system and 11’-6” ceiling heights made
this a good candidate for building renovation and
façade upgrade.

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façade structural element, typical of the
time period. The architect and consultant
assessed the existing façade conditions
and found the 2-story 3”x 6” vertical
mullions fixed to top-of-slab anchors to be
of sound condition, and capable of
supporting an overclad system.
Advantages of overclad (Figure 7.16)
approach claimed by the architect include:
§ material reductions
§ labor reductions
§ avoidance of demolition cost and waste
§ minimized anchor penetrations through
the existing facade
§ installation from outside
This latter minimized disruption to
ongoing building operations.
The glass area was increased by about 16-
inches vertically, utilizing a high-
performance low-e insulated glass unit
(IGU). The lower part of the tower was
built to the property line, requiring that the
overclad system fit between the vertical
mullions, utilizing a mullion jacket with
wings to attach infill panels. The upper
setback areas were more easily mounted to
the surface of the verticals. As is common
with projects of this size, full-scale performance mockups were built and tested for each
section, verifying fit-up as well as moisture and air infiltration performance.
As many as a dozen roof-suspended work platforms were used over multiple shifts to
facilitate installation (Figure 7.17). Each platform could be raised and lowered into

Figure 7.16: Installation of overclad curtainwall
proceeding up left side of front elevation
(Courtesy of MdeAS Architects).

Figure 7.17: Roof area was used as staging for the
many suspended work platforms (Courtesy of
MdeAS Architects).

321
position, carrying 2-3 curtainwall units.
The new curtainwall system was installed
from the outside over multiple shifts
(Figure 7.18). The replacement of the old
glazing followed the progress of the new
system installation. A night crew working
from inside the building pulled the old
glazing out and installed finishing trim-
kits to tie the interior wall to the newly
installed curtainwall. Weiss describes the
curtainwall retrofit as the “lynchpin” of
the redevelopment program.
Vornado’s redevelopment programs
include an explicit sustainability focus.
Weiss claims potential tenants have at the
top of their list of concerns, “what are you
doing for sustainability?” and that
Vornado regards this as a top priority.
Energy saving measures included new
electric chillers and the new energy
efficient façade. The façade retrofit is
credited with $240,000/year savings in
pre-heating and cooling costs during peak
seasons. The renovation resulted in 15
percent total utility savings, about $0.64
per sqft/year. All told, the savings is about
$1/sqft/year. The project qualified for
LEED EB Gold, with an Energy Star
rating of 82. Other sustainability measures
include: green cleaning program,
recycling diversion rate over 80 percent,
and water reduction over 25 percent below LEED baseline.

Figure 7.18: Installation of overclad curtainwall
proceeding up left side of front elevation
(Courtesy of MdeAS Architects).

Figure 7.19: The completed overclad with a higher
performing façade system presents a markedly
different building aesthetic (Courtesy of MdeAS
Architects).

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Weiss expresses the motivation for the redevelopment strategy as higher occupancy and
lease rates. The $100 million plus renovation program also included lobby and entryway
upgrades, new storefront systems, as well as infrastructure modernization including
elevator optimization and a backup generator system as resilience feature. The
redevelopment project was awarded the Building Owners and Managers Association
(BOMA) 2012 Renovated Building of the Year (Vornado n.d.). The renovation is
credited with attraction “top-tier financial firms and other boutique users…” (Doyle
2014). Metals in Construction (2016, 39) reports that post-renovation occupancy quickly
approached 100 percent and that the owner was anticipating double-digit returns on their
investment. Figure 7-19 shows the completed renovation looking perhaps
indistinguishable from a new building.

323
3 Columbus Circle (Figure 7.20)
Metal-framed curtainwall systems have
been used as overclad systems on
buildings with varied original façade
system types, including masonry.
An overclad renovation strategy was used
at 3 Columbus Circle in New York City
(Figure 7.20) as part of a $150 million
renovation intended to reposition the
building as a class A property (WSJ 2014).
Originally a masonry façade with punched
windows, the building owner was intent
upon modernizing the building
appearance, an objective that was not
without controversy (Gardner (2010)
called the retrofit “vandalism in slow
motion.”). Anchor locations for the new
system were developed to accommodate
both the requirements of the new system
and the realities of the existing steel
structure. The masonry façade materials
were removed in the area of the new
anchor locations and the anchor
assemblies fixed to the building structure
(Figure 7.21). A customized, highly glazed
curtainwall system was then installed over the top of the existing masonry façade,
entirely changing the building’s appearance. The building was occupied during
construction, and the existing windows were left intact. As the installation of the new
façade system progressed, workmen removed the original window units and closed the
gaps to the new system with cover panels specially designed for this purpose. This
demonstrates one of the benefits of the overclad strategy: they afford opportunity to
minimize disruption to ongoing building operations that continue unabated through the
renovation process. The overclad system changed entirely the building’s aesthetic (Figure

Figure 7.20: Original masonry façade.
3 Columbus Circle
New York City
built (3 stories): 1922
architect: William Welles Bosworth
addition (22 stories): 1927
architect: Shreve & Lamb
steel structure; masonry façade w/ punched windows
façade renovation: 2010
architect: Gensler
façade contractor: Gamma International
retrofit type: curtainwall overclad
description: original masonry façade left intact.
Overclad with unitized aluminum system using
reflective glass with bluish tint.

324
7-22). It is challenging, if not impossible,
to honor the original aesthetic intent of the
façade with an overclad strategy.
An overclad design produces a cavity
between the old and new systems. It is
most commonly designed to be of
minimal depth and is sealed off in the final
installation. The cavity may incidentally
act as an added thermal buffer, increasing
the u-factor of the wall system and
improving façade performance, and
insulation can be added in opaque areas to
enhance the effect. The overclad strategy
enables potential design variations
through activating the cavity between the old and new systems as part of a performance
design strategy, forming a variation of a
double-skin façade system.
The cavity becomes an opportunity for
developing higher levels of façade
performance, as is common practice with
new double-skin façade system designs. It
can be ventilated to the exterior to reduce
the potential for seasonal overheating,
unvented during cold months to enhance
the effect as a thermal buffer, or even
vented to the interior under favorable
conditions. Overheating should be
considered in the context of elevation and
climate. Greater control of the ventilation
can be achieved by developing a dynamic
climatic response in the façade system that
further improves performance. Shading
systems can be located in the cavity where

Figure 7.21: Anchors have been installed in the
pockets where the brick façade has been
removed. The new system being installed over the
old to the right. (Photo courtesy of Alex Terzich)

Figure 7.22: Post-retrofit appearance is a radical
departure from the original. (author’s photo)

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they can more effectively block solar heat gain, yet are protected from the elements by
the outer skin. Automated cavity venting and shading can be integrated through an
integrated building management system that networks a system of sensors and controls to
provide optimized performance in response to changing climatic conditions. This strategy
has proven effective in new façade designs such as the New York Times Building (Lee et
al. 2013).

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7.5.6 Reclad
A façade reclad involves the complete removal and replacement of the façade system. It
is an expensive undertaking and can be highly disruptive to ongoing building operations
if the building is to remain occupied during construction.
A reclad strategy provides the following advantages (derived from Richards (2015):
§ Greater aesthetic freedom: The façade designer has maximum freedom of
expression in the new building façade in support of modernization goals and
rebranding as part of a building renovation program.
§ Passive/active green performance features: Daylighting design, shading
systems, highly insulated spandrel areas, ventilation and systems integration can
all be incorporated into the new façade design program.
§ Greater freedom of design detailing: The interface is directly between the new
curtainwall system and the building structure. No need to manage the interface
with and penetrations to an existing curtainwall system.
§ High performance technology: A reclad can often make use of the same high-
performance curtainwall systems and glazing products employed in new building
construction.
§ Creation of additional lease area: The potential to push the façade envelope
outward to create additional leasable area.
§ Warranty coverage: Façade retrofit contractors are generally required and
willing to warranty a reclad or overclad strategy as they would the façade system
in a new building application.
A reclad can be a more straightforward option than an overclad because there is no need
to interface with or design around an existing system. If the building is unoccupied, once
the demolition of the existing façade system is complete, the new curtainwall design and
delivery process is essentially the same as for new building construction. This, however,
is seldom the case, as few building owners can afford the loss of revenue represented by a
1-3-year façade renovation process. Reclad challenges include the following:
§ Threat to heritage value: The high cost and complexity of repair and partial
renovation activities may favor overclad or reclad strategies. A curtainwall
overclad will certainly change façade aesthetic. A reclad can attempt to replicate
the look of the original façade, as with Lever House and the UN Secretariat
Building. On vernacular buildings, however, an owner is often interested in

327
modernizing the appearance of the building, among the advantages provided by a
reclad strategy as mentioned above. The preservation community is discovering
heritage value in the vernacular TCB, and some are advocating protection of these
buildings in addition to the icons among them.
§ Survey of existing conditions: A comprehensive survey of the building is
required involving probes of typical and interface areas to determine condition
and configuration.
§ Building structure: The building structure must be evaluated based upon
prevailing code requirements to determine if load capacity is adequate to handle
the new façade system.
§ Redevelopment value: Deep floor plates, shallow ceiling heights, and other
factors my challenge the ability to develop the building value to justify the
investment in renovation.
§ Cost: Reclads are expensive. Richards (2015, 144) notes that reclads are likely to
have a higher cost than other options, partially because they must include the cost
of demolition of the existing system. Analysis of the facaderetrofit.org database
suggests that this may not true. Evidence is provided following that the other
methods categorized here can cost more than reclads because some curtainwall
systems do not facilitate repair, partial renovation or overclad processes.
§ Disruption: Perhaps the biggest challenge of a façade reclad is the disruption to
ongoing building operations, which represents a threat to tenant health and
productivity and a potential liability to the building owner. A reclad can be
extremely invasive, exposing occupants to interruption, noise, dust, fumes and
other effects ranging from inconveniences to life safety threats. Richards (2015,
144) posits that tenants “will almost certainly” need to vacate the building during
the reclad process. Vacating the building for the 1-2 year period of a reclad is an
expensive proposition that brings pressure to bear on keeping the building
occupied and operational during construction. The lost revenue from tenant
relocation makes this strategy unworkable for many owners. Exceptions can be
found with institutional owners, like the United Nations, and the owners of
prestige properties representing building icons, like Lever House; the UN
Secretariat Building and Lever House were both vacated for an extended period
during the façade renovation period. The result is that a building-occupied reclad
is generally driven by strategies to mitigate these impacts to ongoing building
operations.
§ Embodied impacts: Reclads are the most challenging façade retrofit typology in
terms of embodied impacts because of the high energy intensity of the
predominant materials of aluminum and glass.

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§ Waste: Reclads have the highest potential impacts to the solid waste stream.
Aluminum must be carefully recovered and reused or recycled. Glass is a
problem. It is typically not recycled, but can be down-cycled as a fill material.
The last three considerations; disruption, embodied impacts and waste, greatly challenge
the sustainability of reclad practices. The embodied impacts are discussed at length in
chapter 4, with the recommendation that the reclad be reserved for a strategy of last
resort, when no other strategy will practical. Nonetheless, reclad appears to be the most
common façade renovation strategy with metal-framed curtainwall buildings, apparently
because lesser interventions are often unworkable or even more costly. A case in point is
the renovation of the Javits Convention Center in New York City.

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Javits Convention Center
While not technically a tall building, the
curtainwall retrofit of the Javits
Convention Center (Figure 7.23) is
relevant. The Crystal Palace component of
the complex, as the entry hall was
designated by the original architect, James
Ingo Freed of Pei Cobb Freed & Partners,
is 15-stories in height—270’ square in
plan and 180” high (82m x 55m) (Pei
Cobb Freed & Partners n.d.). The 1.6
million sqft (over 148 million sqm)
complex is enclosed with a filigree space
frame structural system clad with a metal-
framed glass curtainwall system of the
same general type as used with tall
buildings. In 2006, the Empire State
Development Corporation, owner of the
facility, selected design firm FXFOWLE
Epstein to lead the renovation team, which
included the façade consulting firm
Heintges.
Note that the service life of Javits is over
twenty years less that the other cases
included in this section, and is the only
one that incorporates insulated glazing, a
practice that was not widely adopted until
after the energy crisis in the 1970s. There
is reason to speculate that the more recent double-glazed curtainwall systems may prove
less durable that the early single-glazed systems. The problem with the IGU is discussed
in Section 4.4.6.
The curtainwall system had undergone some deterioration since its installation in the
early 1980s, but inspection found it to be in “surprisingly good shape,” according to

Figure 7.23: Javits Crystal Palace before reclad
(author’s photo).
Javits Convention Center
New York City
built: 1986
architect: I.M. Pei & Partners ( now Pei Cobb Freed
& Partners)
structure: steel space frame, reinforced concrete
original façade: aluminum stick curtainwall

façade renovation: 2014
developer: Empire State Development Corporation
architect: FXFOWLE Epstein
façade consultant: Heintges
façade contractor: Enclos
retrofit type: unitized aluminum curtainwall overclad
LEED Silver
description: Façade reclad as part of $500 million
renovation; 4-sided structurally glazed unitized
system with field-applied exterior silicone wet seals.

330
Robert Golda (2014), an associate with Heintges at the time and part of the façade retrofit
team. Relatively few of the insulated glass units (IGUs) appeared to have seal failures
and clouding. The brown paint on the aluminum extrusions intended to match the darkish
bronze of the glass had chalked and faded, but not failed. There was some widespread
staining of the exterior glass surface that might have been caused by chemicals leaching
over time from the sealant materials used to weatherproof the façade, which may have
been removable by an appropriate cleaning procedure. No in situ testing was done on the
glass to evaluate this, or to further evaluate the condition of the IGUs, because the
decision was made early on to replace the glass for aesthetic reasons.
The original glass panels (see Figures 7.24, 7.25) combined a gray body tint with a
bronze-colored reflective coating as a strategy to mitigate solar heat gain through the all-
glass façade, which limited light transmission to the building interior and produced a

Figure 7.24: Original 5’x5’ grid with reflective glass (left), and new 5’x10’ module with higher
visible light transmission (right). (author’s photo)

331
mirrored appearance from the outside, effectively creating an opaque façade during
daylight hours.
While state of the art in high-performance glazing at the time, and necessary mitigate
solar heat gain, the glass produced a visual effect far different than the crystalline

Figure 7.26: Another view under different lighting conditions of the new system (left) and the
original (right) (author’s photo).

Figure 7.25: A view to the east from inside reveals the difference in transparency between the
new façade system (left) and the original (right) (author’s photo).

332
transparency envisioned by architect Freed, and so limited light transmission that the
interior of the all-glass enclosure was often described as dark (Seward 2011; Pogrebin
2012). The effect was exacerbated by the 5-foot square (approx. 1.5m) glazing module
used as a subdivision of the 10-foot (approx. 3m) grid of the supporting space frame
structure, which, with the wide mullions characteristic of the time, resulted in further
reduction of daylight reaching the interior.
Heintges performed an extensive survey and evaluation of the existing façade system to
determine options for renovation. Per Golda, “…two complete sets of bid documents
where developed - one for the complete replacement of all systems, and one for the …
refurbishment of the vertical sloped wall systems where the existing aluminum units
[mullions] would remain.” The refurbishment scenario Golda refers to is identified in the
typology in Section 7.51as a selective replacement retrofit strategy, in this case involving
the replacement of the existing glass with a new high-performance product. The complete
replacement of the façade system is the reclad strategy. Both schemes were subsequently
put out for bid, and the cost for the selective replacement retrofit came back
“significantly more” than the replacement scenario. In addition, bidders refused to
provide a warranty for the selective replacement strategy, but were willing to include a
ten-year warranty with their reclad bids.
The decision was made to proceed with the reclad (Figures 7.27 – 7.30). The old
curtainwall system was removed. The façade contractor arranged for the no-cost removal
of the old materials from the site with a recycler, who broke out the glass and reclaimed
most of the aluminum for recycling, sending the glass to landfill. Glass products had
advanced considerably since the time of the original design, particularly in terms of the
high-performance coatings combining the selective reflection of solar heat energy with
high transmission of the visible light spectrum. The new façade design utilized insulated
glazing with a low-e coating that provided higher performance with increased light
transmission (Figures 7.25 and 7.31)

333
Figure 7.27 shows the retrofit
anchors installed to the space
frame to attach the new
curtainwall system. The
developer required that the
renovation accommodate
ongoing Conference Center
operations throughout the
construction process.
Installation logistics drove much
of the project strategy. An
extensive structural system was
built inside the center as a false
roof (Figure 7.29). The
temporary roof structure was
strong enough to act as the floor
for installation activities above,
including materials, lift
equipment, and the extensive
scaffolding providing workmen
access and staging areas for
work on the skylight roof and
facades of the upper Crystal
Palace. (Figure 7.30).
LCA was not performed and no
embodied carbon analysis was
considered. No design service
life was specified for the reclad
façade system.
The approximately $500 million
renovation was completed in
late 2013.

Figure 7.28: Fixing detail of curtainwall system to steel
spaceframe structure (author’s photo).

Figure 7.27: Workers install the new curtainwall system and
new entrances along east elevation (author’s photo.

334

Figure 7.29: A temporary roof structure allowed the convention
center to remain operational throughout the renovation process
(author’s photo).

Figure 7.30: A mass of scaffolding sits atop the temporary roof
structure (Figure 7.29) providing work platforms and access to
the skylight roof (author’s photo).

335

Figure 7.31: As the renovation of the convention center’s 15-story “Crystal Palace” nears
completion, the increased light transmission of the façade system is evident (author’s photo).

336
1271 Avenue of the Americas
Originally the Time & Life Building,
1271 Avenue of the Americas (Figure
7.32) is another of the vintage TCB
stock. Located at Rockefeller Center in
Midtown Manhattan, the building is
undergoing an estimated $325 million
renovation that includes a complete
replacement of 450,000 square feet of
curtainwall. The intent as expressed by
the developer is to retain the iconic
identity of the building and “evolve” it
for the “workplace of the future.” The
renovation program calls for a new
“high-efficiency double-glazed curtain
wall with nearly 60% more vision glass.”
Other improvements include HVAC, and
elevator controls. Renovations were
recently completed to the ground floor
lobby area. (Rockefeller Group 2016)
Daniel Bower (2016) with the
development team says, “We are
restoring the greatest elements of the
building and enhancing its functionality
for a class-A workplace experience.”
The developer recognizes a growing
trend in New York a growing trend in
New York of redeveloping and
repositioning existing building assets as
an alternative to the expensive and time-
consuming process of demolition and
new construction (Rashin 2016).

Figure 7.32: Original façade elevation. (photo
courtesy Filip Maljković)
1271 Avenue of the Americas
New York City
built: 1958
architect: Wallace Harrison of
Harrison, Abramovitz, and Harris
steel structure; 48 stories; 11’ ceiling heights
façade: prefab frames, field glazed

façade renovation: in progress;
expected completion: Q1 2019
developer: The Rockefeller Group
architect: Pei Cobb Freed & Partners
façade consultant: Arup
GC: Turner Construction
façade contractor: W&W Glass
retrofit type: reclad, unitized alum. curtainwall
LEED Gold targeted
description: Designated landmark 2002; ground floor
interior only.

337
A façade reclad is part of the renovation
program; the original façade will be
replaced with a new high-performance
unitized aluminum and glass curtainwall.
The new system will include a higher
window-to-wall ratio (WWR) to bring
more light to the interior and bring a
higher level of transparency to the
building (Pei Cobb Freed & Partners
n.d.a). The lowering of the knee-wall an
increase in vision glass is shown in
Figure 7.33. The changes in the new
system design are evident in (Figure
7.34). As with 330 Madison above, the
original stick curtainwall included large
rectangular outboard vertical extrusions
as a primary structural element of the
façade system. Here they are to be
removed. The new system includes a
more refined T-section profile that still
captures the vertical expression of the
original system. The elements of the
redesign are illustrated in Figures 7.35 -
7.37. Contemporary architectural
glazing products provide the possibility
of higher performance combined with
increased transparency; as Selkowitz
(2017) points out, however, the net gain
is frequently offset by an increase in the WWR, as with the new façade system for this
project. The demand for maximized areas of vision glass in the façade continues.
The development team is taking advantage of Time Inc.’s departure as a tenant, and a
predominance of negotiated subleases, to schedule the renovation. The building will
remain operational but individual floors will be renovated as they are scheduled for
vacancy, with the development team managing remaining tenant relocations as required.

Figure 7.33: Renderings compare the added
vision glass area in the original façade (above)
with the new scheme (below) (courtesy of Pei
Cobb Freed & Partners).

Figure 7.34: Section of original stick curtainwall
above with new unitized reclad scheme below
(courtesy of Pei Cobb Freed & Partners).

338
An email exchange with façade contractor
W&W Glass (Haber 2017) indicated that an
overclad solution was considered, but it was
determined that the existing curtainwall
framing and anchorage would not support an
overclad strategy. The units will be set from
within the building using floor cranes. A
suspended scaffolding rig will be used to
install curtainwall units at mechanical floors,
which do not provide façade access from the
interior for unit-setting purposes. The
unfortunate predominance of asbestos as a
building material in this time period manifests
in the façade system of this building. The
majority of the existing façade is so
contaminated with asbestos that assemblies
will be bagged, removed and disposed of;
recycling was deemed unfeasible. The
monolithic heat-strengthened glass is broken
out of the frames before bagging, and also
disposed of. The experimental nature of these
early metal and glass curtainwall systems
sometimes involved the use of materials and
processes that had not withstood the test of
time. Asbestos is no longer used as a building

Figure 7.37: The progression from left to right reveals the reduction in spandrel area and increase
vision glass module (courtesy of Pei Cobb Freed & Partners).

Figure 7.36: Rendering of new unitized
reclad system, reflecting use of same
overall grid and emphasized verticality as
the original façade design (courtesy of Pei
Cobb Freed & Partners).

Figure 7.35: Rendering including planned
unitized reclad façade system.

339
material, so will not be a problem at the end-of-life of the new system. Perhaps by the
time of the next façade renovation of this building the glass will be recycled. No
provision is made in the new curtainwall design for future retrofit.

340
7.5.7 Heritage building façade retrofits
There is growing appreciate for the heritage value of twentieth century artifacts of
Modernism, including the midcentury TCB (Jerome and Ayón 2014, 14). Early icons of
this period include the Seagram Building (1958, New York City, Ludwig Mies van der
Rohe, Philip Johnson), Lever House (1952, Gordon Bunshaft and Natalie de Blois,
Skidmore Owings and Merrill), and the U.N. Secretariat Building (1952, New York City,
Oscar Niemeyer, Le Corbusier, Wallace Harrison). While many TCBs of this period have
yet to undergo major façade renovation, two of these three have undergone façade
restorations that involved the complete replacement of the curtainwall system. The
curtainwall systems of each were in bad shape by the time of their restoration. Lever
House had been granted landmark status by the New York City Landmarks Preservation
Committee in 1982, but the façade system was well past its prime even by that time, with
rusted components and mismatched glass replacement panels. The façade restoration was
completed in 2001 (Stephens 2003).
Preservation considerations of heritage buildings bring another dimension of challenge to
the already complex process of façade renovation, especially with respect to the
character-defining metal and glass curtainwall systems of TCBs. The next section
examines the façade renovation of the U.N. Secretariat Building completed in 2013.

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United Nations Secretariat
Heintges (2017) credits the Secretariat
Tower (Figure 7.38) as “one of the most
widely-recognized examples of 20th
century International Style architecture,”
and the first TCB in the U.S. It is also
among the first to undergo a considered
restoration (Lever House, another iconic
New York City TCB also completed in
1952, underwent a façade restoration in
2001). The building design was not the
effort of a single firm, but a collaborative
team of leading practitioners of the time,
keen on using the newly available
technologies of glass and aluminum to
express a new post-war vision of
modernity and transparency.
Alderstein (2015a, 370) claims the
Secretariat Building as the “prototype for
all modern curtain wall office towers,”
but the prototype facades had
deteriorated significantly over nearly 60
years and were in need of intervention.
Heintges (2017), the design architect for
the façade restoration, describes the
existing façade system as “comprised of
glazed curtain walls with double-hung
windows, spandrels of blue-green tinted
glass, and a grid of louvered frames at
the mechanical floors and the parapet
level” (Figure 7.39). Clearly defined
project goals included upgrading and
modernization to meet or exceed all
relevant code requirements while

Figure 7.38: Original façade system, west
elevation, circa. 2007. Note the reflectivity. (photo
credit I, Padraic Ryan).
United Nations Secretariat
New York City
built: 1952
architect: Le Corbusier, Oscar Niemeyer, Wallace
Harrison, others.
steel structure; 39 stories
façade: single-glazed curtainwall with thermally
unbroken aluminum and steel framing

façade renovation: 2013
developer: United Nations
façade designer and consultant: Heintges &
Associates
GC:
façade contractor: Benson
retrofit type: reclad, unitized alum. curtainwall
LEED Platinum
description: Occupants were relocated during the two
year curtainwall restoration.

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restoring the original character of the facades; sustainability, security, performance and
history were expressed as integral to all considerations.
Seasonal condensation and moisture infiltration has become a problem with many of
these buildings. The earliest examples of this building type sometimes included mild steel
frames and anchors, as was the case with Lever House; this proved to be the weak link in
the curtainwall system, leading to its replacement in 2001 (Hart, 2003). The UN
Secretariat façade had begun to deteriorate after only a few years of completion (Ayón
and Rappaport, 19).
Heintges performed extensive research and evaluation of the original facades, including
system probes from suspended scaffolding rigs. Their findings included:
§ lost transparency due to the application of a reflective film on the glass
§ visual continuity due to off-color replacement glass
§ corrosion of aluminum mullions and deterioration of finishes
§ multiple layers of caulking repairs
§ high percentage of corroded anchors that could not meet wind load requirements
§ inadequate thermal performance and energy efficiency
§ inadequate security protection
The new reclad curtainwall incorporated a thermally broken, dual seal and pressure-
equalized aluminum framing system. Extrusions are as close in section to the originals,
being slightly larger to accommodate the additional thickness of insulated glazing. Some
of the extrusions were offset to replicate the original appearance of the double-hung
windows (Alderstein 2015a, 373). A finishing procedure utilizing clear anodizing was
developed to match that of the original extrusions. High performance glass selection and
specification took a full year and involved computer simulations, measurement and
comparison of spectral and optical data under varying conditions of day and season, and
ultimately, a full-scale onsite mockup—the ultimate strategy for evaluating the
appearance of architectural glass (Patterson and Vaglio 2011b, 56). Heintges (2017)
claims the strategy was successful in restoring the long-lost tint and transparency of the
original facades (Figures 7.39 and 7.43).
Alderstein (2015a, 374) provides details of the renovation process. The Tower was
vacated for the installation of the reclad. A “swing space” strategy was employed,

343
involving the relocation of over 6,000 staff to other quarters spread around the City. A
few hundred were relocated each weekend starting in 2010, with a similarly staged return
in 2012. Significant disruption characterizes curtainwall replacement, whether the
building is vacated or occupied during the construction process. Few building owners can
afford the two-year loss of revenues resulting from the former. The U.N. renovation
program was comprehensive, with scope well beyond the curtainwall systems on the
Secretariat, but the final project cost was $2.2 billion. The strategy used and on other
iconic TCBs like Lever House is unlikely to work on the vernacular candidates of the
vintage TCB stock.
The original curtainwall system was preassembled in single-story ladders, attached to the
concrete floor slabs, then infilled with window sashes and glass. The installation of the
new unitized curtainwall system was facilitated by an elaborate multistory suspended
scaffold spanning the full breadth of the façade elevation (Figure 7.40), rigged from a
temporary cantilevered supporting structure built from the building’s roof (Figure 41).
Figure 7.39: West elevation in process façade installation; old system below mechanical floor
grills, new system above. Reflectivity of old façade caused by application of a solar film. The new
façade is intended to restore the original glazing tint (authors photo).

344
The access rig was positioned per a
construction schedule, with the
restoration proceeding bottom to top in
10-story zones between the louvered
mechanical levels (Alderstein 2015a,
373), completing full width horizontal
bands of new façade before
repositioning the access rig. The work
platform allowed workers to access the
façade from inside and out. The old
system was disassembled, pulled inside
the building, and hauled away. A
construction lift was used to move
materials to and from ground level
(Figure 7.42). New anchorages were
installed to steel reinforcing structure.
Crates of new curtainwall units made
their way up the construction lift, and
were installed using floor cranes.
Heintges (2017) notes the dilemma of
preservation standards conflicting with
today’s performance expectations, and
adopted a strategy to achieve, “a faithful
reconstruction” that honored the design
intent of the original architects, with
minimal modifications as required to
meet contemporary standards. They
claim the Secretariat Tower sets a new
standard for the renovation of vintage
TCBs, and credits the team’s expertise
with knowledge of materials, fabrication and procurement processes. Alderstein (2015a,
375) agrees, commenting that even with “conflicting budgetary, programmatic and
security demands, a highly sustainable renovation…can be executed…fully respecting
the character defining features of the building.” He credits the new curtainwall of the

Figure 7.40: Suspended scaffolding rig provides
work area for demolition of old and installation of
new curtainwall systems (author’s photo).

Figure 7.41: Detail of temporary outrigger structure
to suspend scaffolding rig (author’s photo).

345
Secretariat Building with the
achievement of LEED Platinum,
noting the following attributes:
§ 50 percent increase in energy
efficiency and 45 percent reduction
in emissions as compared to pre-
renovation performance,
§ 90 percent of occupied spaces
have access to daylighting and views
with new daylight harvesting system,
§ 95 percent of construction waste
diverted from landfill/
Alderstein (2016) also assess the
embodied carbon advantage of the
reuse of buildings and building
systems in the overall United Nations
Headquarters renovation, which
involved the entire campus, in
avoiding demolition and
replacement, the only project encountered in the case study research that spoke to the
issue of embodied carbon. The report finds that it would have taken 35 – 70 years to
recoup the embodied carbon debt of new construction from improved operating
efficiencies in the new construction. The report even points to the time-value of carbon,
emphasizing that expenditure of embodied carbon in the short term to replace existing
buildings may be counter-productive if the payback is decades in the future. However,
the same claim can be made regarding any expenditures for energy efficiency
improvements, such as the façade replacement for the Secretariat Building, which was,
unfortunately, not subject to the same assessment, but surely represented a significant
expenditure of embodied energy. The motivation to minimize the façade intervention
seems to be absent from all but the more ardent preservationists, and some building
owners. Owners interested primarily in remediation and not modernization may prefer
minimal intervention to reduce costs. For the preservationist, minimal interventions are a
means to mitigate risk of alteration to the original façade design and technology. In this

Figure 7.42: Construction lift on east elevation used to
move old materials out and new materials in (author’s
photo).

346
case, these motivations may most closely align with sustainable outcomes in façade
retrofit, even if there are no explicit sustainability goals in the renovation program.

Figure 7.43: View of completed east elevation from the East River on an overcast day (author’s
photo).

347
Table 7.3 summarizes key data from the case studies.
The case studies included in this section provide examples of the façade renovation
typology developed in 7.5.1. They range from discrete, minimal interventions like 60
Broad Street, through overclads making partial use of existing façade assemblies, to
commercial reclads like 1271 Avenue of the Stars, to all out restoration driven reclads
like the Secretariat Building. A few variants are examined along the way, like 3
Columbus Circle—an overclad of an existing masonry building, and Javits—a reclad of a
space frame convention center. The example cases fit the typology scheme, but the
emphasis on case-by-case evaluation with the TCB building type must be remembered;
there are a great many variations of these basic renovation types both existing and
potential, driven by the wide variations in the existing building stock and their respective
façade systems. Each renovation project represents a new and different context with its
own set of considerations, limitations and requirements. There are often substantial
differences between them, even when limited to the TCB type. Important differences can
extend well beyond technical considerations, and into the makeup of a project: the
stakeholders, their motivations, the program scope, budget and deliver strategy, the
project budget, goals and timeframe, all of these and more.
Table 7.3: Summary of case study data in Section 7.5. (cost in USD).
name built renovate type motivation scope
approx.
cost
60 Broad St 1962 2014 SER remediation facade 2.5 m
330 Madison Ave 1963 2012 overclad repositioning
façade, lobby, entry,
mechanical, lighting,
interiors
100-120 m
3 Columbus Circle 1922 2010 overclad repositioning
façade, lobby, entry,
mechanical, lighting,
interiors
150 m
Javits Center 1986 2014 reclad modernization
façades, skylight roofs,
entrances, interior
500 m
1271 Ave of the Stars 1958 2019 reclad repositioning
façade, entry,
mechanical, lighting,
interiors
325 m
Secretariat 1952 2013 reclad modernization,
security,
performance,
preservation
facades, structure
upgrades, lobby,
mechanical, interiors,
multi-building campus
2.2 b

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The selection of a type for application on a specific project must be carefully considered
based on a rigorous assessment of the existing building and façade conditions, the
neighboring urban habitat, the owner’s interests, the available technology, and the many
other variables that must be balanced just to arrive at an appropriate methodology. Like
new curtainwall system design, retrofit systems may benefit from consideration of the
sustainability guidelines in Section 4.5.
Given these many variables, the collection of more data and further additional case
studies as a resource for industry practitioners could be of great benefit. This is the
intention of facaderetrofit.org, and an opportunity for future work. However, there are
some observations that can be drawn from the limited case investigation above with
respect to the sustainability of these retrofit practices.
Challenging the sustainability of façade retrofit practices, Section 4.5 “Guidelines to
enhance façade system sustainability through considerations of durability and embodied
carbon” establishes the context for evaluation.
§ Only 60 Broad Street evidences some consideration of material selection and
embodied carbon, although the renovation strategy seems largely driven by the
available budget. The Secretariat Building renovation involved the consideration
of building reuse and embodied carbon, and the most aggressive sustainability
goals of the project sampling, but these considerations did not filter down to the
level of the façade system, which was driven predominantly by the balancing of
strong aesthetic criteria with a desired increase in operational energy efficiencies.
§ None of the project establish a design service life, although Jerome and Ayon
(2014) posit a predicted service life for the SER strategy on this project at 20
years, extendable through appropriate maintenance strategies.
§ None of the case study projects included LCA.
§ While Alderstein (2016) discusses the relevance of the time value of carbon,
again this sensibility does not filter down to the renovation of the façade system.
The SER strategy of 60 Broad Street is clearly superior in this respect, but the cost
in terms of operational carbon emissions is not assessed.
§ 60 Broad Street is the only façade renovation to suggest a maintenance plan to
support design service life.
§ None of the reclad or overclad cases evidence a system design that anticipates and
facilitates the next façade renovation.

349
§ Reclad and overclad system designs for the cases fail to embed adaptive capacity
as required to establish maintainability, repairability and upgradability.
If an SER strategy of doing the least for the most is viable in terms of the time value of
carbon, if not lifecycle carbon footprint, then 60 Broad Street may be the most
sustainable model of the cases examined here.
It is also worth noting, as discussed in Section 9.1, is that the challenges presented by
façade renovation of TCBs result largely from the failure to anticipate and accommodate
the need for future renovation in the design of the original façade system, a behavior that
persists in façade design practices today.
7.6 Reclad: The problem with façade system replacement
As the body of completed facade renovations has been growing for more than a decade,
yet with a great many more buildings in need of some form of façade intervention, there
is great potential opportunity in the evaluation of these renovations, their motivations,
strategies, methods and results. A recently developed beta resource in recognition of this
opportunity was facilitated by a seed funding grant through the Council for Tall
Buildings and Urban Habitat and is currently administered by the Façade Tectonics
Institute. Facaderetrofit.org is an online tool and searchable database of buildings that
have undergone façade renovations. The database currently includes over 500 buildings
worldwide of various types and with varying façade systems ranging from masonry with
windows to curtainwalls (Martinez et al. 2015).
The initial population of the database—new retrofit cases can now be submitted online by
the public and are vetted by Institute staff—was initiated by two surveys with a combined
total of 448 respondents involving over 400 individual buildings (Martinez et al. 2015a).
Two significant findings of the surveys seem to indicate that preservation considerations
are relatively uncommon in these façade renovation programs:
1. Motive: First was the response to the motivation for the façade renovation, which
was predominantly aesthetically driven; an image upgrade as part of a
modernization program. Only 18% in survey-2 indicated preservation
considerations as part of the renovation program.

350
2. Renovation type: Second was the retrofit program type, which was
predominantly reclad, meaning that the entire original or existing façade system
was removed and replaced. Of the 215 curtainwall buildings of 12 stories and
over currently in the database, over half of the façade renovation programs are
reported as complete façade replacements. This is generally the costliest and most
disruptive form of façade retrofit, but the reasons for its predominance in tall
building applications are several. What the data is reflecting is that reclad is often
the only viable option.
Figure 7.4.4 charts additional scope items from the survey.

Figure 7.44: Scope items reported from the original surveys indicate the potential for change to
building appearance.
Another documentation effort focused exclusively on culturally significant Modern
buildings with steel-frame glazed enclosures in the U.S. and Europe (Ayón and
Pottgiesser 2016) determined that, for a variety of reasons, most interventions on both
side of the Atlantic result in replacement just as much as on restoration. Although based
on a statistically small number of samples, the study determined that rehabilitation of
steel-frame glazed assemblies was limited to ten to twenty percent of the interventions.
22%
27%
30%
37%
33%
18%
48%
14%
6%
48%
14%
50%
0%
12%
56%
39%
30%
44%
33%
18%
68%
26%
0% 10% 20% 30% 40% 50% 60% 70% 80%
OTHER
REPAIRS
GLASS FILMS ADDED/REMOVED
WINDOW REPLACEMENT/RENOVATION
INSULATION ADDED
SUNSHADES ADDED
NEW CLADDING MATERIALS ADDED
VISION GLASS REPLACED
OPAQUE PANELS REPLACED
ENTIRE CURTAINWALL REPLACED
OVERCLAD (ORIGINAL FAÇADE RETAINED)
Facade Renovation Scope of Work
Survey1 Survey2

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While the data for these studies is suggestive, more study is required to accurately
determine patterns, trends, motivations, barriers, and other relevant data to façade
intervention in this building type.
Other researches have noted the predominance of replacement as façade renovation
strategy (Henket 1996; 14).
While curtainwall intervention options and their relative use will benefit from ongoing
analysis, there are important considerations and potential problems with replacement as a
dominant strategy, including high monetary cost, disruptions to ongoing building
operations, hidden costs, and motivation.
7.6.1 High monetary cost
Even in strong economic times, curtainwall renovations for many midcentury tall
buildings in need are not forthcoming because of the costs involved with complete façade
replacement, generally as part of a larger renovation program of the building. The trend
of green building retrofits adopted by many owners is limited to the low-hanging fruit of
electrical lighting and HVAC mechanical system upgrades, stopping short of the façade
system for reasons of cost and disruption. The logistics and work area access constraints
involving tall buildings in dense urban environments add to the cost, as do critical
measures to mitigate disruption to occupants through the construction process.
Postponing the replacement of underperforming façades delays the improvement of
interior environmental quality and the provision of comfort necessary for health and
productivity of the building users.
McKeown (2017) discusses the high cost of upgrades and the time to recover these
expenses as effective barriers that prevent owners from pursuing efficiency
improvements in their properties. Access to funding is also a problem for building
owners. Table 7.3 shows the huge range of costs associated with building renovation.
Façade renovation is often a component of a larger building renovation. Building
repositioning is a dominant building renovation scenario in which a developer renovates
with the goal of attracting better tenants willing to pay higher lease rates, and improving
overall building occupancy rates. This often involves elevating the building to class A
real estate standards. Successes with this strategy are noted in the case studies, and
financers appear willing to lend money in this pursuit. These are big dollar numbers.

352
Lenders may be less willing to finance SER strategies like 60 Broad Street, even though
the required amounts are far less. The availability of financing is a key factor in
propagating existing building upgrades.
7.6.2 Disruption to ongoing building Operations
The process of removing and replacing a curtainwall system in an occupied building can
be disruptive in the extreme. Few building owners or organizations can afford to vacate
or relocate occupants during the roughly two-year duration characteristic of curtainwall
replacement on a tall building, as was done by the United Nations for the Secretariat
building renovation (Adlerstein 2015). While this may help speed the renovation work, it
does not avoid the disruption; the UN Headquarters renovation involved the temporary
relocation of 6,000 workers, a process that in itself is inherently disruptive. With
buildings that will remain occupied during construction, mitigating disruption to ongoing
building operations during construction becomes the overriding priority of façade
replacement in an effort to reduce risk to the building owner for productivity losses by
the tenants. Means-and-methods strategies to accommodate this concern are complex and
costly, involving the construction of temporary barrier walls, evening and overnight
work, complicated exterior rigging and work platforms and can even drive the design of
the replacement façade system, as in the case of an overclad strategy. Even so, occupants
are often exposed to construction noise, dust and debris that can pose a threat to health,
comfort, and productivity (World GBC 2014; Browning et al. 2012). People spend a
significant part of their lives in the workspace; two years is a long time to live with this
kind of disruption.
The typical focus on building system durability encompasses economic and
environmental impacts. Consideration of the problem of TCB façade renovation, façade
system reveals a social dimension, what amounts to embodied social impacts. These have
been suggested by others (Iselen and Lemer 1993, 1), but studies specific to the impacts
resulting from curtainwall renovation practices on occupant comfort, health and
productivity were not identified in this research, making this an area of potential future
study. The manifestations include:
§ Relocation to a temporary facility during construction phase of renovation
§ Exposure to dust, debris, noise pollution, and otherwise compromised service
quality in buildings occupied during construction phase of renovation

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Mitigating the effects on building occupants during the construction phase of façade
renovation, in buildings that remain occupied, often becomes the driver of program
logistics. Owners are frequently willing to absorb higher costs for construction strategies
that mitigate their potential liability to claims of compromised health and productivity
from tenants. This is a challenge. Construction is inherently messy and noisy. Sound
pollution is a major problem. Curtainwall systems are typically supported by the building
structure through support plates embedded in the floor slabs. A renovation program
involving the reinforcement or replacement of these plates would necessitate hammer-
drilling or other processes to modify the slab condition, producing structure-borne sound
extremely resistant to mitigation efforts. Investment in oversizing curtainwall embed and
anchor plates in new building construction could provide a hedge against the
uncertainties of climate change and escalating building code requirements.
While the health and productivity impacts of curtainwall renovation practices may be
largely unquantified, a growing body of research has linked comfort, health and
productivity of building occupants to building façade effects of daylight, view and natural
ventilation (Farley and Veitch 2001; Kaplan et al. 1998; Boyce et al. 2003).
7.6.3 Hidden cost
The same arguments for reuse and rehabilitation of a building can be applied to the
building skin; the greenest curtainwall may well be the existing curtainwall. But options
for system rehabilitation short of removal and replacement are few and often impractical,
and may be as expensive or more so than a replacement strategy, as evidenced by the
Javits case study. The costs of embodied impacts are rarely considered, and end up
accompanying the façade renovation as a hidden cost. Aluminum and glass are both high
in embodied energy. While some significant percentage of aluminum is typically
recycled, architectural glass is not, ending up down-cycled or as landfill. In addition, the
high cost of façade replacement may in some cases tip the scale in favor of building
demolition and reconstruction, at an even greater embodied energy cost. The
displacement and disruption of tenants can test social resilience at the local level as
patterns of building use change to more lucrative models.
As yet, there is not identified case of materials from the original facade being reused in a
replacement curtainwall system. Aesthetic modernization goals and economic pressures

354
to use divergent materials—larger glass panes, higher-performing or lower cost materials,
assemblies, and design variations—increases the likelihood of compromise to heritage
value as commercial pursuits take priority over preservation considerations. Few
curtainwall replacements involve preservation goals. The Secretariat is one, documented
above as a case study. Another is Lever House, renovated in 2001, and is a rare case of a
complete façade removal and its faithful restoration. Even here, detail modifications were
made to accommodate the use of larger glass panes (Hart 2003, 126), and the results were
controversial (Curtis 2002, 46; Stephens 2003, 123).
7.6.4 Motivational factors and selection of façade renovation type
Motivation is a factor in achieving outcomes that support sustainability. The motivation
of the developer on a façade renovation project is a dominant factor in project outcomes.
The motivation will shape the project outcome through the definition of the renovation
program for the project, and the goals that are defined as part of that program.
Little research is evident in studying the linkages between motivation, goals and
sustainability outcomes in new construction and renovation projects. The results of two
surveys on building façade retrofits was reported in Martinez et al. (2015; 2015a; 2015b).
The results of the first prompted the addition of questions aimed at further exploring
these considerations (Martinez et al. 2015a). Responses included over 300 buildings,
most built in the 1960s and 1970s, of all façade and building types; midcentury Modern
buildings represented 56 percent of the total (Martinez et al. 2015b, 28). Sixty percent
were office buildings. Over 57 percent can be categorized as tall buildings (over 14
stories). Seventy percent were curtainwall buildings. While the dataset is not strictly
limited to TCBs, they appear to comprise the dominant building type.
Findings included that
§ Energy efficiency is a relatively recent and uncommon motivation for retrofit.
§ Image improvement and modernization—largely aesthetic enhancements—were
the primary motivation cited for the building facade renovations, with the
dominant focus on appearance rather than performance.
§ Energy performance rated second after image upgrade in survey 1, but last in
survey 2, with only 20 percent of projects reporting this as the leading motivation.

355
Simply put, the majority of reported façade renovation projects were driven by
considerations of appearance, not performance. A significant percentage of the façade
renovation activity appears not to be significantly engaging sustainability objectives.
Questions were added to survey 2 to further assess goals and motivations of the
renovation projects and to test correlation of goals with activities that may support
sustainable performance outcomes. Note the results indicated in Figures 7.45 and 7.46.

356

Figure 7.45: Survey response to goals as a component of façade renovation program (Martinez et al. 2015a).

Figure 7.46: Survey response to design and analysis strategies included in façade renovation program
(Martinez et al. 2015a).

357
Findings derived from these responses include:
§ Operational energy use was a leading goal in 57% of projects, but whole building
energy modeling was included in only 40 percent of projects.
§ Durability was a predominant concern, equal to energy use, but durability
planning was reported in only 15 percent of projects.
§ Embodied energy and carbon reduction, resilience and adaptability goals were the
least common goals to be included in façade renovation programs, all under 15
percent.
§ Lifecycle considerations like LCA and LCCA, along with zero net energy-ready
(ZNE-ready) strategies, are rarely integrated into the renovation programs.
§ Health and comfort was a predominant goal at 41 percent, but daylighting design
was included in only 26 percent of projects, indoor air quality in 9 percent,
thermal comfort modeling was higher at 29 percent, but is fundamental to health
and comfort and should match that goal of 41 percent.
§ Acoustic performance was a leading motivation at 23 percent, but acoustic
analysis was included in only 11 percent of projects.
§ One third of the façade retrofit projects reported adoption of none of the activities
associated with sustainable performance outcomes.
There is an apparent mismatch between the expressed goals of the renovation projects
and the strategies that are adopted to realize those goals. This data is interesting but
largely inconclusive at this point, and worthy of further study. Correlation needs to be
established between these goals and strategies and the actual outcomes of these projects
in hard metrics of lifecycle carbon, health and productivity, and other measures that are
not available for the façade renovation projects that comprise the dataset. Still, there is a
strong sense of relevance here, and an opportunity for future work.
More generally, the developer’s interest is largely to improve the economic value of the
building through increased lease and occupancy rates, thereby increasing the revenue
stream to the owner. This often involves the pursuit of a bump in the classification of the
building under the Building Owners and Managers Association rating system (BOMA
2016) for commercial properties, from a class B to a class A, for example. This building
renovation type may result in incidental improvements to performance, but that
likelihood increases if the renovation program adopts a green standard or certification
program like a LEED certification, with a focus on energy efficiency and other

358
considerations in support of sustainable development. There are clear links between
embracing sustainability goals and improved energy performance in building projects
(Kuziemko 2015), which seems logical. Yet renovation projects often fail to define
explicit sustainability goals. It also seems logical that such projects would not perform as
well as their peers.
A relatively recent type of building renovation is the building energy retrofit with the
motive of reducing building operational energy consumption (Hart et al. 2013). While
building energy retrofits do characteristically embrace performance goals related to
energy consumption, they generally stop short of any significant façade intervention
owing to the substantial cost and disruption that accompany such work. Green upgrades
to HVAC, mechanical, lighting, and control systems can, in fact, can represent
appreciable energy efficiency gains, but fail to achieve the integration between the façade
system and these other major building systems that could provide optimized performance
results. For example, energy upgrades will involve the use of a larger HVAC system than
would be required when coupled with a new high-performance façade system. The same
is true of lighting systems when paired with a façade system designed to optimize
daylight distribution with integrated solar control (e.g., an automated roller blind or
louver system) (Tzempelikos et al. 2007). A problem is that in a future of incremental
increases in mandatory energy performance as the building sector steps toward net-zero
carbon, an owner that declines to include the façade in an energy retrofit and proceeds
with the installation of a new energy-efficient HVAC system tuned to the existing dated
façade, may find it necessary to replace the façade system in the near term. Driven by a
first-cost mentality, the owner may replace the façade while maintaining the now
oversized HVAC plant. This pattern creates the potential for cycles of inefficiency as a
series of compromised partial renovations over a building’s lifespan. Systems integration,
lifecycle thinking, and whole-building design practices are the preventive measures to
address this scenario.
Owners ultimately drive a building project. Building owners, often in conjunction with a
team of consultants and advisors, develop the goals and directives that are passed on to
the design and build teams. These instructions reflect the motivations of the owner. There
are important differences among building projects based on owner type. The General
Services Administration (GSA) through its Public Building Service (PBS) is the largest
public real estate organization in the U.S. with 376.9 million square feet of space in 9,600

359
federally owned and leased buildings (GSA 2013). The GSA embraced Obama era White
House initiatives to increase sustainability and energy efficiency throughout government
by committing to the greening of its building stock. In 2010 the GSA adopted LEED
Gold certification as the minimum standard for new federal building construction and
substantial renovations (GSA 2010; Hartke 2013). As of June 2016, GSA’s portfolio of
buildings includes 154 LEED certifications, including 49