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Mitigating thermal bridging in ventilated rainscreen envelope construction: Methods to reduce thermal transfer in net-zero envelope optimization

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Mitigating thermal bridging in ventilated rainscreen envelope construction: Methods to reduce thermal transfer in net-zero envelope optimization

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MITIGATING THERMAL BRIDGING IN VENTILATED RAINSCREEN ENVELOPE
CONSTRUCTION:

METHODS TO REDUCE THERMAL TRANSFER IN NET-ZERO ENVELOPE OPTIMIZATION

by

Michael Grauer

A Thesis Presented to the
FACULTY OF THE USC SCHOOL OF ARCHITECTURE
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
MASTER OF BUILDING SCIENCE

AUGUST 2018

i

COMMITTEE

CHAIR:

Kyle Konis, A.I.A., Ph.D.
Assistant Professor
USC School of Architecture
kkonis@usc.edu

COMMITTEE MEMBER #2:

Joon-Ho Choi, Ph.D.
Assistant Professor
USC School of Architecture
joonhoch@usc.edu

COMMITTEE MEMBER #3:

Douglas Noble, FAIA, Ph.D.
Director of the Graduate Building Science Program
Chair of the Ph.D program
USC School of Architecture
dnoble@usc.edu
(213)740-4589

TECHNICAL ADVISOR:

Matthew Brooke-Peat, FAIA, Ph.D.
Course Director – Architectural Technology
School of the Built Environment and Engineering
Leeds Beckett University
121 Northern Terrace
Queens Square Court
Leeds
LS2 8AG
m.brooke-peat@leedsbecket.ac.uk
0113 8121730

ii

ABSTRACT
In the United State, strategies to measure and mitigate Thermal Bridging are not as common place as those required
in the European Union (EU) and detailed by the International Organization for Standardization (ISO). The
distinction between regulatory requirements, construction methods, preferred materials, and bio-climatic conditions
necessities an assessment of Thermal Bridging contribution to building energy performance within the context of the
United States building, regulatory and construction environs. The additional impact of Thermal Bridging on heat
transmission loss is not part of mandated energy calculations in which the U-value of the wall assembly is the only
metric for façade performance. This research will examine typical thermal bridging locations and details based on
popular ventilated rainscreen systems (face brick, thin brick, fibre cement panel, aluminum panel and phenolic
panel) and access their contribution to envelope heat transmission loss. Thermal performance analysis will be based
on current ISO, ASHRAE, NFRC and EU requirements. Then, the details (method of construction) and materials
will be revised and/or augmented in an attempt to mitigate energy consumption and increase envelope performance.
The final results will be assessed based on the performance criteria of a net-zero energy building (NZEB).

As the number of verified and emerging Net-Zero Energy Buildings (NZEB) increases in the United States,
strategies to reduce thermal loads imposed by bio-climatic conditions become an essential ingredient in reducing
building Energy Use Intensity (EUI) toward a neutral balance between renewable and non-renewable energy
sources. The contextual relationship between a buildings thermal envelope design and annual energy performance
represents the primary research environment to measure the effects of Thermal Bridging junctions on overall
building efficiency. The analysis of Thermal Bridges through the application of specified construction assemblies
within the NZEB research prototype is an effective approach to facilitate research comparisons at the micro, meso
and macro envelope scale.

Although, products and strategies are available to mitigate the effects of Thermal Bridging these tend to be
supplemental elements applied to established methods of façade construction. This research will analyze the
supplemental approach and then seek to improve performance through a reassessment of facade system
methodology, material science and fabrication processes. The basis of all assessed strategies and construction
assembly iteration will be the specific regulatory restrictions, construction processes and bio-climatic conditions
common within the United States. Performative analysis and conclusions will be examined within this context.

HYPOTHESIS
Accurate building envelope performance assessment requires analysis of thermal bridging contributions which are
dependent on specific construction material and assembly processes. Accurate energy use analysis requires U-value,
Psi-value and Y-value contributions simulated for all applicable construction details.

RESEARCH QUESTIONS
• What is the contribution of thermal bridging to the reduction of envelope thermal resistance
based on common North American rainscreen assembly construction?
• How can thermal bridging be mitigated using select thermal break material applications?
Which materials represent the best value in terms of adaptive applications per designated
detail locations?
• Based on the designated rainscreen assemblies, which application have the best performance
per ASHRAE climate zone based on a contextual NZEB energy model.

iii

TABLE OF CONTENTS

Chapter 1: Introduction 1
1.1 Introduction 1
1.1.1 R-Value 3
1.1.2 U-Value / U-Factor 3
1.1.3 Thermal Bridging 3
1.1.4 K Value ( λ ) 3
1.1.5 Chi Value ( x ) 4
1.1.6 Psi Value ( Ψ ) 4
1.1.7 Transmission Heat Loss Coefficient (HTB) 4
1.1.8 Y Factor Value 4
1.1.9 Types of Thermal Bridges and Heat Flow Calculations 5
1.1.10 Relavent Standards for Simulation 6
1.1.11 Humidity, Temperature and Condensation Control 6
1.1.12 Stategies for Mitigating Thermal Bridges 6

1.2.1 Net Zero Energy Buildings 8
1.2.2 Net Zero Building system boundaries and Thermal Bridging 8
1.2.3 Energy Budget 8
1.2.4 Prescriptive Approach 9
1.2.5 Performance Approach 9

1.3.1 Rainscreens 9
1.3.2 Types of Construction 10
1.3.3 Types of Fasteners and Attachments 11
1.3.4 Insulation Requirements per Climate Zone 13

Chapter 2: Previous Work: Background and Literature Review 17
2.1 Literature Review 17
2.1.1 Calculation Methods 17
2.1.2 Thermal Inertia 18
2.1.3 Underestimation of Thermal Loads 19
2.1.4 Rainscreen Performance 19
2.1.5 Net-Zero 19

2.2 Simulation Software Review 20
2.2.1 Flixo Pro www.flixo.com 20
2.2.2 AnTherm www.antherm.at 20
2.2.3 DesignBuilder www.designbuilder.co.uk 20

2.3 Summary 21

Chapter 3: Methodology 22
3.1 Introduction - Research Questions 22
3.1.1 Methodology Diagram 23
3.1.2 Method of analysis and selected constraints 24
3.1.3 Designated Assembly Types 40
3.1.4 Typical Detail Locations 43

22
1
iv

Chapter 4a: Pressure Equalized Rainscreen Assembly Analysis 44
4a.1 Introduction 44
4a.1.1 Contribution of air and weather barrier system to mitigation of heat transfer thru a PER
assembly fastener attachment.
45
4a.1.2 Contribution of exterior façade panel material to heat transfer thru a PER assembly
subframe.
46
4a.1.3 Aluminum vs Galvanized Steel Subframe Analysis 47
4a.1.4 Fastener Material Analysis 48
4a.2 Results Summary 49

Chapter 4b: Thermal Bridge Analysis – Assemblies per Detail Location 53
4b.1 Introduction 53
4b.1.1 Wall assembly analysis – clear field 54
4b.1.2 Roof assembly analysis 55
4b.1.3 Elevated building structure analysis 56
4b.1.4 Typical window sill and jamb analysis 57
4b.1.5 Base and head of wall at ground level analysis 58
4b.1.6 Spandrel and soffit assembly analysis 59
4b.1.7 Roof parapet assembly analysis 60
4b.1.8 Corner assembly analysis 61
4b.1.9 Canopy extension analysis 62
4b.2 Y-Value non-repeating linear thermal bridging calculations 64
4b.3 Results Summary 68

Chapter 4c: Contextual Whole Building Energy Analysis 69
4c.1 Introduction 69
4c.1.1 Contextual energy simulation : Climate zone 1A – Miami Florida 70
4c.1.2 Contextual energy simulation : Climate zone 2A – Houston Texas 71
4c.1.3 Contextual energy simulation : Climate zone 3B – Los Angeles California 72
4c.1.4 Contextual energy simulation : Climate zone 4A – Baltimore Maryland 73
4c.1.5 Contextual energy simulation : Climate zone 5A – Chicago Illinois 74
4c.1.6 Contextual energy simulation : Climate zone 6A – Minneapolis Minnesota 75
4c.1.7 Contextual energy simulation : Climate zone 7 – Duluth Minnesota 76
4c.1.8 Contextual energy simulation : Climate zone 8 – Fairbanks Alaska 77
4c.1.9 Energy Use Intensity per climate zone and assembly type 78
4c.1.10 Thermal bridging contributions to annual source energy per climate zone 78
4c.2 Results Summary 80

Chapter 5: Summary of Findings and Discussion 83
5.1 Discussion Introduction 83
5.2 What is the contribution of thermal bridging to the reduction of building envelope thermal
resistance based on common North American rainscreen assembly construction?

83
5.3 How can thermal bridging be mitigated using select thermal break material applications? Which
material represents the best value in terms of adaptive applications per designated detail locations?

84
5.4 Based on designated rainscreen assemblies, which application(s) have the best performance per
ASHRAE climate zone based on the contextual NZEB energy model?
85
v

5.5 Implications for current energy modeling and evaluation procedures 86
5.6 Implications for current regulatory requirements regarding mandatory envelope performance
factors and energy budgets
86
5.7 Limitations and future work 87

Chapter 6: Conclusions 88
6.1 Conclusions 88

Bibliography 90
Appendix A
SAP 2016 : BRE Governments Standard Assessment Procedure, Appendix R, Table R2 :
Reference Values of psi for junctions (England)
93
Appendix B
Architectural Details 95
Appendix C
Thermal Bridging Analysis Results 106
Appendix D
Glossary of Terms, Acronyms and Abbreviations 116
Appendix E
Y-Value Calculations 117

88
vi

1

CHAPTER 1

1. INTRODUCTION

1.1 Introduction
In the United State, strategies to measure and mitigate thermal bridging are not as common place as those required
in the European Union (EU) and detailed by the International Organization for Standardization (ISO).The additional
impact of Thermal Bridging on heat transmission loss is not part of mandated energy calculations in which the U-
value of the wall assembly is the only metric for façade performance. This research will examine typical thermal
bridging locations and details based on popular ventilated rainscreen systems (face brick, thin brick, fibre cement
panel, aluminum panel and phenolic panel) and access their contribution to envelope heat transmission loss. Thermal
performance analysis will be based on current ISO, ASHRAE, NFRC and EU requirements. Then, the details
(method of construction) and materials will be revised and/or augmented in an attempt to mitigate energy
consumption and increase envelope performance. The final results will be assessed based on the performance
criteria of a net-zero energy building (NZEB).

Envelope codes and standards related to building energy efficiency in the United States do not account for Thermal
Bridging effects which decrease envelope performance and reduce the effective R and U value of envelope
components. Typical codes and standards mandate a minimum or maximum weighted U-factor for a wall, window
or roof assembly based on climate zone. This is called the Prescriptive Approach to building energy efficiency in
which thermal values are based on an overall annual energy budget for each building typology. Inefficiencies
imposed on the envelope by thermal conduction related to the interface of thermally conductive materials at
transitional conditions are not considered. The impact of these Thermal Bridges on annual energy efficiency is not
considered relevant to overall energy efficiency, although research has shown that they can range from 5%-20% of
total heat flow through the building envelope (Theodoros, 2015). This underestimation of heat loss has obvious
impacts on mechanical system efficiency and thermal comfort and is especially critical in buildings which are
attempting to achieve Net Zero annual energy consumption (NZEB). Within an NZEB framework, inefficiency
created by Thermal Bridging conditions will result in additional offsets required from renewable energy sources. For
this reason, it is important to understand the effects of Thermal Bridging within the context of the regulatory code
requirements and construction trade custom and practice in the United States.

In comparison, the member states which comprise the European Union have integrated Thermal Bridging
calculations and mitigation as a mandatory measure regulated through each countries building code. Thermal
Bridging values must either be calculated at all specified junctions and interfaces, or an accredited construction
detail with a minimum thermal conduction value must be used (Staf Roels, 2011). This additional requirement added
to the prescriptive approach ensures that heat flow and related energy efficiencies are more accurately controlled
throughout the building envelope. However, construction trade custom and practice in the EU varies greatly from
common construction techniques and assemblies in the United States, so these accredited constructing details and
prescribed Thermal Bridging values are not accurately adaptable to the United States construction market, climate
zones and regulatory environment.

The design of a building envelope for a NZEB in the United States should be a combination of the current European
standard regarding Thermal Bridging calculation and mitigation and the regulatory framework and construction
methods required in the United States. Best practices related to the design and construction of a NZEB in the United
States will diverge from those in Europe for these reasons and others including climate, cost, and applicable
optimization of the assembly within the ascribed context. A key design priority for NZEB buildings is a focus on
improved efficiency before any renewable energy strategies are contemplated for the design. These include load
reduction, passive systems, energy recovery and active efficiency strategies (ARUP, 2012); all of which can be
affected by Thermal Bridging conduction through the building envelope. The same performance metrics which are
currently used to measure NZEB building performance can be used to contextualize the specific performative
contribution of typical Thermal Bridging junctions within a standard building typology. Energy Use Intensity (EUI)
metrics for NZEB are based on two primary factors : Site-kBtu which is measure in kBtu/ft
2
/yr and TDV (Time
Dependent Valuation). These factors are critical in ascribing the required size of renewable source per NZEB
(ARUP, 2012).

2

Simulation of conventional wall assembly details within the context of the 8 ASHRAE climate zones will represent
the baseline performance for design iteration and NZEB calculation. A series of mitigative interventions utilizing
low-conductivity materials will be applied to the conventional details to increase thermal performance. Finally, the
conventional and mitigated details will be assessed in a contextual whole-building energy model to measure their
effect on annual energy performance toward a NZEB. All details designated for analysis will be based on specific
constraints related to methods of construction and regulatory requirements common in the United States. Given the
predominance of NZEB buildings in the office, educational and research sectors, all details will be based on
mandatory structural and envelope requirements associated with Type I and Type II construction classifications per
the 2016 International Building Code. Details will focus primarily on 3 types of ventilated rainscreen envelope
assemblies within the context of a non-combustible structural frame, floors and roof assembly. Non-load bearing
exterior walls will be constructed using common cold-formed metal framing construction and all sheathing will be
fiberglass matt gysum wallboard.

Although, products and strategies are available to mitigate the effects of thermal bridging these tend to be
supplemental elements applied to established methods of façade construction. This research will analyze the
supplemental approach and then seek to improve performance through a reassessment of facade system
methodology, material science and fabrication processes. Each designated assembly will be analyzed for its
contribution to NZEB performance associated with Thermal Bridging. Once completed, specific mitigation
strategies will be applied to these details and re-assessed to measure the presumed reduction in heat transfer and
NZEB performance. Mitigation strategies which precipitate the most effective performative improvement will
assessed for cost and constructability.

3

1.1.1. R-value (Thermal Resistance)
R-value represents the capacity of an insulating material or building component to resist heat flow. Resistance value
is expressed in m
2
C°/W or ft
2
F°hr/Btu. (International Code Council, 2018)
R=ΔT/QA
Q A= Heat transfer per unit time per unit area

1.1.2. U-Value and U-Factor (Thermal Transmittance)
U-factor represents the overall coefficient of thermal transmittance of a fenestration, wall, floor or roof/ceiling
component expressed in Btu/ ft
2
F°hr or W/m
2
K; including air film resistance on both sides. (International Code
Council, 2018)
U= 1/R = QA /ΔT
U O or U EQUIV represents the clear field thermal transmittance of a wall assembly. This value includes uniformly
distributed point (x) Thermal Bridges which are integral to a specific wall assembly type and not typically calculated
on an individual basis. The clear field U-value adjusts the heat flow coefficient to account for these point thermal
transmissions expressed in W/m
2
K – see 1.1.5. (Morrison Hershfield Limited, 2016)
1.1.3. Thermal Bridging
Thermal Bridging is the transfer of heat through an area or element of a building’s envelope which has significantly
higher heat transfer than the surrounding materials resulting in an overall reduction in thermal insulation of the
element or building.
Thermal bridges can occur at any thermal discontinuity in which materials with higher thermal conductivity create a
pathway for heat flow through the envelope assembly. The primary pathway for heat flow through the building
envelope is at locations of metal framing, metal attachments or fixings, structural steel framing and/or concrete
construction. (National Institute of Building Sciences, 2017)
Heat is transferred through the building envelope via three modes : conduction, convection and radiation. All three
modes of heat transfer require a temperature difference between the exterior boundary and interior boundary of the
assembly. Heat is always transferred in the direction of the lower temperature. Through conduction, energy is
transferred across solid conductive materials such as concrete and metal. Convection transfers heat by a fluid or gas
medium; most commonly the air within a wall or glazing cavity. Radiation can transfer heat through surface absorption
and transmission at the molecular level. (National Institute of Building Sciences, 2017)

1.1.4. K Value / Lambda Value ( λ )
K or Lambda value represents the value of thermal conductivity of a building material or product under specific
internal and external conditions, which can be considered as typical of the performance of that material or product
when incorporated in a building component. Lambda values are expressed in W/mK and are used to calculate
insulating capacity of a product or assembly, but they are not dependent on the thickness of material. (International
Organization for Standardization, 2007)

4

1.1.5. Chi-Value ( x )
Chi-value represents the value of thermal conductivity of a building material at a localized condition, also known as
point thermal transmission and expressed in w/K. The influence of point thermal transmission is typically neglected
at conditions where a linear thermal bridge also occurs per ISO 14683. However, when substantial point transmission
conditions occur at repeating penetrations due to fittings and/or attachments then they should be accounted for based
on ISO 10211. (International Organization for Standardization, 2017) Due to the complicated nature of this
calculation, point thermal transmissions are rarely accounted for in building energy modeling. (Theodoros, 2015)
Chi-Value formula :

1.1.6. PSI Value ( Ψ )
Psi value represents the rate of heat flow per degree Kelvin per unit length of bridge (i.e. 1 meter) that is not accounted
for in the U-values of the plane building elements containing the bridge. The heat loss associated with the non-repeated
thermal bridge is called linear thermal transmittance or Psi-Value or Ψ-value. Psi values (W/mK) are used to calculate
the Y value (W/m
2
K). (International Organization for Standardization, 2007)

1.1.7. Transmission Heat Loss Coefficient (HTB)
The H TB coefficient represents the aggregate product of two factors; the Psi value multiplied by the length of the linear
Thermal Bridge. The H TB coefficient is represented in units as W/K.
Transmission heat loss formula with non-repeating thermal bridges :

H
TB
= Σ ( L x Ψ )

1.1.8. Y-Factor Value
Y-Factor value represents the thermal bridge heat loss expressed per square meter of envelope area. Building envelope
Y-values are calculated by multiplying the Psi value by the length of the corresponding thermal bridge condition. We
then aggregate these results. This aggregate figure is known as the transmission heat transfer coefficient or H TB. To
calculate a Y-value the H TB, for which the unit is W/K, is divided by the total external area of the building, not
including the party walls or in the case of a cold pitch roof, the warm ceiling area. This will then give a Y-value,
usually e.g. 0.04 and in the same units as the U-value i.e. W/m2 K. (International Organization for Standardization,
2007)
Y-value formula :
Y = H
TB
/ Σ A
EXP
5

1.1.9. Types of Thermal Bridges and Heat Flow Calculations
Thermal Bridges are classified based on the following types :
Material Thermal Bridges : Thermally conductive element which penetrates an insulating layer.
Geometric Thermal Bridges : Occur when the heat-emitting surface is larger than the heat absorbing
surface. Building corners are a typical example.
Linear Thermal Bridges : Heat flow in the steady-state divided by length and by the temperature difference
between the environments on either side of the bridge. (International Organization for Standardization,
2007)
Point Thermal Bridges : Heat flow in the steady-state divided by the temperature difference between the
environments on either side of the bridge.The point thermal transmittance is a quantity describing the
influence of a point thermal bridge on the total heat flow. (International Organization for Standardization,
2007)
Clear Field Thermal Bridges : Heat flow in steady-state divided by the temperature difference between the
environments on either side of the bridge. The clear field U-value is an overall assembly transmittance
coefficient which includes integral point thermal transmittance created by fittings, fasteners, and frames
within the construction. (Morrison Hershfield Limited, 2016)

Fig. 1-1 Types of Thermal Bridges

Heat Flow Calculations
Overall Heat Flow Calculation : Q = Σ (Ψ*l) + Σ (X) + QO
Heat Flow per Area : U = (Σ (Ψ*l) + Σ (X)) / A + U0
Wall effective U – Value per wall area : Q = Σ (Ψ*l) + QO ; QO = UO*A ; U = Q/A = UEFF

6

1.1.10. Relevant Standards for Simulations
ANSI / NFRC 100-102 ; Technical standards that establish uniform procedures for determining the various energy
performance ratings : including U-factor, Solar Heat Gain Coefficient (SHGC), Visible Transmittance (VT), and
Condensation Resistance. The procedures detailed by ANSI/NFRC are used to certify fenestration products based on
these performative measurement methods. (National Fenestration Rating Council, 2013)
EN ISO 10077-2 : 2017 ; specifies a method and gives reference input data for the calculation of the thermal
transmittance of frame profiles and of the linear thermal transmittance of their junction with glazing or opaque panels.
Key value requirements:
• Equivalent U-Value – takes into account the effects of periodic thermal bridges
• Psi – Value - rate of heat flow caused by a thermal bridge
• Edge Psi-Value – thermal evaluation of spacers and glazing edges
ASHRAE 90.1 – 2016 ; establishes prescriptive wall insulation requirements based on 8 climate zones in North
America. Specifies a maximum effect U-Value per construction assembly type.
These standards will form the basis of simulation analysis including interior and exterior temperature and prescribed
overall U-factors of baseline assemblies.

European Assessment Standards
The following European standards and prescribed thermal bridging values will be used as reference:
• BRE IP 1/06 Assessing the effects of thermal bridging at junctions and around openings (UK)
o Y=.15 W/m
2
K (existing construction)
o Y=.08 W/m
2
K (new construction)
o Y=.04 W/m
2
K (new construction when thermally modeled)

• DIN V 4108-6 (Germany)
o Y=.05 W/m
2
K ( all construction)

1.1.11. Humidity, Temperature and Condensation Control
The higher the insulation level of a building component is the less heat is available for its drying. Consequently,
increased air tightness of the building envelope can affect indoor humidity levels and create hydrothermal surface
conditions which precipitate mold growth. The analysis of these specific hydrothermal conditions within the building
envelope can eliminate condensation and eventual mold growth within the assembly. Thermal Bridging within the
context of interior or exterior climatic conditions, can create cold areas where warm, moisture-laden air condenses on
cold surfaces and materials. Although, condensation control is not a primary focus of this research, it will be necessary
to ensure that increased possibility of condensation and mold growth do not undermine the performative value of any
mitigation strategy. Per current EU regulatory standards, a temperature factor f rsi shall be ≥ .75 to avoid the risk of
mold growth. (International Organization for Standardization, 2017)

1.1.12. Stategies for Mitigating Thermal Bridges
The National Fenestration Rating Council (NFRC) defines a thermal break as a material of low thermal conductivity
that is inserted between members of high thermal conductivity in order to reduce heat transfer. Thermal barrier
7

material conductivity shall not be more than 0.52 W/Mk (3.60 Btu-in/h-ft
2
-F°). (National Fenestration Rating
Council, 2013). Strategies for mitigating heat transfer at Thermal Bridges includes the use of low conductivity
material spacers, shims, wraps and attachment elements used to separate or replace thermally conductive penetrating
elements. The following list of materials provides common materials which can be employed toward Thermal
Bridge reduction in envelope assemblies:

Table 1-1
MATERIAL CONDUCTIVITY
W/m
2
K
DESIGN THERMAL
CONDUCTIVITY
W/mK - λ
DENSITY
kg/m
3
-

ρ
SPECIFIC
HEAT
CAPACITY
J/kgK Cρ
EMMISIVITY
COEFFICIENT ϵ
Neoprene .05 0.23 1240 2140 .94
PVC .19 0.17 1390 900 .91
Gypsum
(5/8” thick)
.17 0.18 600 1000 .85
Fiberglass
(pultruded)
.04 0.40 1900 700 .75
Bitumen .17 0.23 1100 1000 .90
Polymide .3 .25 1150 1120 .90
Aerogel - .036 540 1310 .75
XPS .029 0,025 1200 .90
EDPM .25 0.25 1150 1000 .90
AIR .024 0.025 1.23 1008 -
HDPE .50 .50 980 1800 .91
(International Organization of Standardization, 2007)
Numerous product offerings are now available with the construction market which claim to reduce the effects of
Thermal Bridging through the use of low-conductance materials. All of these products utilize materials indicated in
table 1-1 to fabricate a pre-engineered attachment system which combines low-conductance materials and structural
support systems. Products A-C, A-D and A-E represent mitigation strategies applied directly to primary load paths at
the structural frame and deck which require a specific engineered solution. However, products A-A and A-B have
simply extended the effects of a low-conductance shim or spacer to form a framing or attachment member. It is unclear
if the mitigating effect is greater with these applications and the use of a simple shim or spacer of the same material
composition.

A-A Engineered rainscreen subframe clips and offset brackets A-B Composite engineered z-clip
8

A-C Structural frame connection insulator A-D Fluid applied thermal break A-E Balcony slab insulator
Fig. 1-2

1.2.1 Net Zero Energy Buildings
A Net Zero Energy Building (NZEB) produces enough renewable energy to meet its own annual energy consumption
requirements, thereby reducing the use of non-renewable energy in the building sector. NZEBs use all cost-effective
measures to reduce energy usage through energy efficiency and include renewable energy systems that produce
enough energy to meet remaining energy needs. The characteristics and components of a NZEB envelope include
required levels for thermal transmittance, thermal bridges, air tightness and solar protection (shading). (International
Organization for Standardization, 2013)
1.2.2 Net Zero System Boundaries and Thermal Bridging
Establishing a cost optimal NET Zero energy building requires the use of a detailed system boundary with inclusion
of on-site renewable energy production. A building envelope optimized for fixed specific heat loss values requires an
effective combination of insulation levels for windows, exterior walls, slab on grade and roof assemblies. Thermal
Bridges represent areas of weak performance which must be addressed for optimized heat loss resistance. The addition
of a Y-factor value in NET Zero energy simulations is critical to accurate performance results; U-value calculations
alone do not provide a comprehensive analysis of heat loss through the building envelope. (Charisi, 2017)
1.2.3 Energy Budget and Energy Demand
Common metrics for measuring building energy use consist of site energy, source energy, energy use intensity (EUI)
and time dependent valuation (TDV). These metrics are used, depending on compliance pathway and regulator, to
measure the energy used by a building and set efficiency limits based on that use. Site-kBtu is the most common
metric based on an equivalency of input and output energy where both are valued equally. The limitation of Site-kBtu
is that it does not account for additional potential cost associated with capacity or conversion. It is also not useful for
annual energy use comparisons between different buildings.
Comparative energy use is based on Site Energy Use Intensity or EUI which is calculated as Site-kBtu / area; a
buildings EUI is an expression of its energy use and size or other characteristics. The Environmental Protection
Agency (EPA) has established an EUI calculation method which utilizes Source Energy-kBtu / area as the basis for
their EnergyStar score. Source energy which factors energy production and transmission is considered a more
equitable method of energy evaluation. EUI is considered a useful comparative indicator between different buildings
annual energy use. (International Organization for Standardization, 2013)
Time Dependent Valuation (TDV) is a metric which does not value energy directly; but values energy based on
influencing variables. These include capacity, conversion, offsets and supply / demand balancing. (ARUP, 2012) TDV
is specific to California, but has advantages for NZEB building calculations in that the amount of renewables required
are significantly lower as compared to Site-kBtu. (ARUP, 2012)

9

1.2.4 Prescriptive Approach (building energy compliance)
A building must comply with envelope requirements based on maximum weighted U-factor calculations of envelope
assembly materials. The prescriptive approach mandates required performance values for envelope, space
conditioning, lighting and power consumption per building typology. This method ensures energy code compliance
by controlling the minimum efficiency of the envelope and system energy consumption. This approach allows for less
flexibility in envelope construction and system selection and can result in a poor cost-to-efficiency ratio. Prescriptive
approaches have mandatory minimum and maximum requirements for energy performance based on climate zone.
(International Code Council, 2018)

1.2.5 Performance Approach (building energy compliance)
A building complies with the performance standard if the energy budget calculated is not greater than the standard
design building calculated as the sum of energy based on the application of the mandatory and prescriptive
requirements. Performance based compliance is based on a validated energy model simulation. This approach allows
for more flexibility in design and energy efficiency tradeoffs between envelope performance and system energy
consumption. This approach can capture cost saving in construction material, equipment, labor and annual energy
consumption. (International Code Council, 2018)

1.3.1 Rainscreen Wall Systems
Rainscreen Wall Systems can be simply defined as an envelope assembly with two distinct planes separated by a
ventilation or drainage cavity. The interior plane is the primary weather barrier located at the structural boundary of
the assembly. The exterior plane is the secondary weather barrier and usually consists of an open or closed joint
cladding layer. The air gap between these planes creates a pressure difference to reduce water infiltration and/or allows
for the drainage of incidental water which can penetrate the joints of the assembly at the exterior plane. From a thermal
resistance perspective, the cavity between the exterior and interior planes can be utilized to increase effective envelope
performance through the application of continuous insulation (c.i.) and continuous air barrier layers. The continuous
insulation (c.i.) layer is separated from interruption by framing members within the structural boundary which
contribute to thermal bridging. The continuous air barrier reduces air infiltration through the envelope from exterior
wind and interior mechanical systems. (Metal Construction Association, 2006)

Type of Rainscreen Wall Systems
Pressure Equilized Rainscreen (PER) assemblies use the ventilation cavity to create a net-zero pressure differential
between the outside air pressure and the air pressure within the ventilation cavity. This reduces pressure induced water
penetration beyond the exterior plane of the assembly reducing / eliminating water penetration to the interior plane.
PER system require effective engineering of the ventilation cavity to achieve dynamic pressure equalization
throughout the assembly. (Metal Construction Association, 2006)
Drainage Plane Rainscreen (DPR) assemblies are not engineered for pressure equalization and do not have open joints
or vents in the exterior plane. Drainage planes are located at the interior plane of the assembly and are designed to
remove water which may penetrate the exterior plane at joints and transitions. Effective drainage of rainwater requires
a drainage plane as small as 1/8” or as large as 1” depending on the moisture load and material construction of the
exterior plane. DPR systems are typically utilized in masonry veneer applications like architectural plaster, full brick
and thin brick veneer and exterior tile and stone veneer. (Metal Construction Association, 2006)
10

Type of Subframe Attachment System
The installation of a panelized rainscreen system requires an engineered subframe to support the panels on the exterior
side of the sheathing layer. These subframes are typically comprised of metal support girts or furring fastened directly,
or indirectly, by screw type fasteners through the sheathing into the corresponding steel stud wall construction. Indirect
attachments are primarily comprised of ‘L’ shape clips which offset the continuous support members from the
continuous insulation layer which is also attached through the sheathing. These are all engineered systems which
require support calculations to derive the type of subframe member, spacing of attachment and spacing of panel joint
based on applicable structural loads. There are three types of subframes offered for analysis in this research:
• ACRIC : Aluminum Clip, Rail and Interlocking Channel - This is a pre-engineered subframe system which
is purchased by the installer from the manufacturer engineered for a specific application. This system requires
a stainless-steel fastener due to the dissimilar metals connection between aluminum clip and steel stud.
• GALV : Galvanized steel continuous Z-girt and furring – This subframe is comprised of standard framing
members and is typically engineered by the installer.
• FBGLS CLIP : Pultruded fiberglass clip system – Support clips are fabricated with a low-conductivity
material to reduce thermal transfer from the exterior ventilation cavity, through the fastener, into the building.
These clips are typically 4-5” wide and require (2) fasteners each.

Fig. 1-3
Typical PER Rainscreen
Assembly
Fig. 1-4
Typical PER Rainscreen Assembly – Face
Brick
Fig. 1-5
Typical DPR Rainscreen Assembly
– Architectural Plaster

1.3.2 Types of Construction
There are five types of construction classifications with the United States based on fire resistance and occupancy
requirements within an overall life safety regulatory framework. Type I and Type II construction represent the most
restrictive classification of construction materials. The respective restriction of combustible materials in the structural
frame and envelope result in an increased probability of Thermal Bridging through material conduction. For this
reason, all details analyzed shall be based on Type I and Type II requirements. (International Code Council, 2015)
Specific requirements are as follows:
• No use of wood members
• Structural steel frame shall be applied with cementitious spray-applied fireproofing
• Composite metal floor and roof decks shall be 2 hr fire resistant construction.
• Light gauge metal stud framing shall be used of all non-load bearing exterior wall assemblies.
11

• Fiberglass mat gypsum wallboard shall be used for all sheathing
• Slab-on-grade construction
• R-30 roof assembly with single-ply roof membrane

1.3.3 Types of Fasteners and Attachments
Metallic fasteners, attachments and support framing are the primary conduits of heat flow through the building
envelope. Even when the penetrating attachment is surrounded with insulating material, the conductivity of any
metallic surface can greatly diminish the effective R and U value of the surrounding assembly. Lambda (λ) values
which designate the thermal conductivity of a material can be over 100x’s greater for metals than any other applicable
building materials. The following lambda (λ) values are specific to common metal construction components related
to PER and DPR assembles :
• Aluminum - lambda (λ) = 160 W/mK
• Steel - lambda (λ) = 50 W/ mK
• Stainless steel, austenitic - lambda (λ) = 17 W/ Mk
• Zinc - lambda (λ) = 110 W/ mK
Typical Fastener Types and Assembly Applications

Fig. 1-6
#10 Sheet Metal Screw for Cold-Formed Metal Framing
These are primarily flat or pan head in framing applications.
Steel screw with zinc finish
Fig. 1-7
Typical Cold-Formed Metal Framing at
Exterior Wall.

Fig. 1-8
#2 Phillips Undercut or Bugle Head for FM Gypsum
Sheathing Attachment. Steel screw with phosphate or
Zinc finish.
Fig. 1-9
Fiberglass Mat Gypsum Sheathing at Exterior Wall.
12

Fig. 1-10
#10 Tech Screw with 5/16” head w self-sealing washer.
Stainless Steel (austenitic) screw or steel with zinc
coating
Fig. 1-11
Offset clip and subframe assembly attachments

Fig. 1-12
#2 Phillips Undercut or Bugle Head Extended Screw
with 2” Diameter plastic washer for C.I. Insulation.
Steel screw with phosphate or Zinc finish.
Fig. 1-13
PER assembly c.i. insulation fastener with plastic
washer. Rigid plastic or mineral wool insulation.

Fig. 1-14
#2 Phillips Undercut or Bugle Head Extended Screw
with 2” Diameter plastic washer for Expanded Metal
Lath. Steel screw with phosphate or Zinc finish.
Fig.1-15
DPR assembly metal lath and assembly fastener with
plastic washer.
13

1.3.4 Insulation Requirements per Climate Zone
U-value requirements for walls, roofs, floors, doors and fenestration are specified based on a variety of factors
enumerated by the local building code. The selection of an opaque wall assembly type and its insulation value should
always be based on the specific bio-climatic factors represented by a buildings location and the requirements of the
local authority having jurisdiction (AHJ) over building construction. While colder climates can assume increased
levels of insulation, adverse effects from over-insulation of a building can affect air quality and energy efficiency in
specific bio-climatic conditions and building uses.
The adoption of building code regulations by local and state jurisdiction has three primary sources; the IECC -
International Energy Conservation Code, ASHRAE 90.1 and the DOE - Department of Energy. It is from these sources
that state authorities adopt or create specific building envelope requirements applicable to their jurisdictions. Most
adopt code language and compliance paths from these sources without revision, but some states with specific bio-
climatic conditions and regulatory discretion write and publish requirements specific to their state. The primary
example of this is the state of California which has its own building code, regulations, and climate zones independent
of the national standard.
Insulation values for opaque wall construction may be determined through the prescriptive or performance based
compliance path. Prescriptive envelope insulation requirements are established based on climate zone, building type,
building height and type of construction. Based on these criteria, minimum U-values are assigned based on a weighted-
average. Weighted averages must be calculated and submitted to the local jurisdiction to prove that discrete
combinations of assemblies and areas sum to the minimum prescriptive total allowed by the code. An area-weighted
average R-value or U-value estimates the efficiency of a whole building section, considering variations in surfaces,
structure and materials. These prescriptive values are also typically used as a baseline for preliminary design when
using the performance based compliance path. Prescriptive values used for initial energy calculations can be reduced
and offset with other energy savings in a performance-based approach. (International Code Council, 2018)
The minimum acceptable insulation requirements for opaque walls are specific to construction type, which are
designated as:
• Metal buildings
• Metal framed buildings
• Wood framed buildings
• Mass walls
o Weighing not less than 35 psf of wall surface area.
o Weighing not less than 25 psf of wall surface area.
o Having a heat capacity of 7 Btu/ft
2

o Having a heat capacity of 5 Btu/ft
2

(International Code Council, 2018)
Requirements for continuous insulation (c.i.) are not part of every adopted code requirement. Some jurisdictions may
mandate the amount of continuous insulation required per prescriptive criteria, while others assume that some amount
of continuous insulation must be used to meet the prescriptive U-values imposed and allow for some flexibility for
designers to specify the construction of the wall. In addition, the IECC and ASHRAE publish differing requirements
for insulation values within the same climate zones. This can result in specific building locations having conflicting
prescriptive insulation requirements when referenced in the IECC and ASHRAE standards. These differences, imply
that the designation of envelope performance values allow for some amount of deviation based on the assumed energy
budget and climate conditions.
The insulation of footings (and slab edge) is mandated for frost protection in heated buildings per specific local
building codes. The required amount of insulation is dependent on a scheduled air-freezing index of values which
increases the required insulation from a minimum of R 4.5 to a maximum of R 10.1 based on the freezing severity of
the climate zone. This requirement may not be incorporated in jurisdictions with temperate or hot climates. However,
there may still be a measurable benefit to the application of this insulation to mitigate heat loss associated with thermal
14

bridging in slab-on-grade construction when applied to the perimeter edge / face of slab . (International Code Council,
2018)
The application of insulation and reduction of an assemblies U-factor is not a panacea for building energy efficiency.
Insulation restricts heat on an exponential scale which means that as the thickness of insulation increases its ability to
restrict heat flow decreases. Eventually, adding additional insulation no longer reduces buildings energy consumption.
In some cases, it may even increase energy consumption by trapping heat from equipment loads inside the building;
this heat will need to be removed by the mechanical system. (Kim, 2009) The diminishing returns from increased R-
value (or decreased U -value) will scale differently based on climate zone.

Fig 1-16 Insulation and Heat Flow (www.energyvanguard.com)

The IECC and ASHRAE base their envelope performance requirements on the same 8 climate zones as divided across
the continental United States, Alaska and Hawaii. Within these 8 climate zones, each city is subdivided by thermal
criteria and designated as A-moist, B-Dry and C-marine. These thermal criteria designations are defined based on
mean temperature and humidity. Common examples of these climates zone are as follows:
• New York, New York : 4A
• Chicago, Illinois : 5A
• Las Vegas, Nevada : 3B
• Hawaii : 1A

Additionally, state and local jurisdictions may designate climate zones based on specific bio-climatic conditions and
related envelope performance requirements which the IECC and ASHRAE requirements do not consider. The State
of California is an example of climate zones defined by local bio-climatic nuances which target building performance
within a more explicit context.

15

Fig. 1-17 California Climate Zones

Window-to-wall ratio (WWR) is another important factor to consider when assessing prescriptive, weighted-average
insulation values. Glazed areas of the façade will have U-values which are considerably lower than the opaque areas;
the difference between glazed and opaque wall assembly U-values can be as great as 90%. Calculating a weighted-
average can result in very high insulation values required for opaque areas to offset the performance of glazing. This
can make a prescriptive approach untenable for many projects and will necessitate the use of the performance based
method. Ultimately, in a performance-based approach the insulating value of the envelope will be a reflection of the
energy performance of the building and mandatory minimum U-value requirements.

16

ASHRAE CLIMATE ZONES

Fig. 1-18
METAL FRAMED OPAQUE WALL INSULATION VALUES PER CLIMATE ZONE (PERSCRIPTIVE)
Above grade wall assemblies – assume 6” steel stud primary wall framing commercial construction only.
CLIMATE
ZONE
ASHRAE 90.1 -
2016
c.i. MINERAL
FIBER INSUL*
c.i. XPS ** IECC - 2015 c.i. MINERAL
FIBER INSUL*
c.i. XPS **
1 R-13 N/A N/A R-13 + 5 c.i. 1.19” 1”
2 R-13 + 9.8 c.i. 2.18” 1.96” R-13 + 5 c.i. 1.19” 1”
3 R-13 + 5 c.i. 1.19” 1” R-13 + 7.5 c.i. 1.8” 1.5”
4 R-13 + 7.5 c.i. 1.8” 1.5” R-13 + 7.5 c.i. 1.8” 1.5”
5 R-13 + 10 c.i. 2.4” 2” R-13 + 7.5 c.i. 1.8” 1.5”
6 R-13 + 12.5 c.i. 3” 2.5” R-13 + 7.5 c.i. 1.8” 1.5”
7 R-13 + 12.5 c.i. 3” 2.5” R-13 + 7.5 c.i. 1.8” 1.5”
8 R-13 + 18.8 c.i. 4.5” 3.76” R-13 + 7.5 c.i. 1.8” 1.5”
(ASHRAE, 2016)
* Values based on Roxul CavityRock mineral fiber board insulation: R-value / inch at 75°F = 4.2hr-ft
2-
F/Btu
** Values based on extruded polystyrene foam insulation: R-value / inch at 75°F = 5.0 hr-ft
2-
F/Btu
Assume 3.5” fiberglass batt insulation (R-13) within the steel stud framing cavity.

17

CHAPTER 2

2. PREVIOUS WORK : BACKGROUND AND LITERATURE

2.1 Introduction
The following references provide the performance and analysis framework for all simulations conducted in support
of this thesis. This section investigates some of the work previous scholars have done regarding building envelope
and proposed simulation software.

2.1.1 Calculation Methods
There are currently four calculation methods which enable inclusion of an envelopes thermal performance values
into a whole-building energy model simulation. Each method requires a specific software simulation process and the
application of a details Thermal Bridging calculated value to be integrated into the thermal envelope of the energy
model. The accuracy of transfer from Thermal Bridging calculation to whole-building simulation differentiates the
four approaches. (Baba & Ge, 2015)
Equivalent U-Value Method
The equivalent U-value method incorporates the effects of Thermal Bridging into a whole-building energy model
through adjustment of the envelopes insulation value. Typically, this is accomplished by reducing the thickness of
the insulation until the designated U-value of the wall assembly type is equivalent to the performance of the wall
assembly including the effects of the Thermal Bridge. In the United States and Canada, the equivalent U-value is
typically calculated by a two-dimensional conduction, heat transfer analysis computer program like Therm. (Baba &
Ge, 2015) This analysis is considered steady-state because the environmental variable which effect the system do
not change over time. Although, this method is effective in accounting for overall thermal transmittance, the
dynamic heat flows which occur at linear transitions and junctions and point thermal transmissions which occur at
attachments are ignored or incorrectly calculated. At these defined detail junctions it is necessary to calculate the
assemblies Psi - Value ( Ψ ) and use this value within the whole-building energy simulation.

One-dimensional parallel transmission calculations assume a simple area of influence for thermal conduction. The
actual area of Thermal Bridge is dependent on an assembly’s construction and corresponding sensitivity to lateral
and multi-directional heat flows through material of high conductance. Corners (horizontal and vertical) and
transitional junctions are especially vulnerable to underestimation using this calculation approach. (Morrison
Hershfield Limited, 2016)

Combined Thermal Properties Method (CTP)

The CTP method adjusts the thermal conductivity of both the insulation layer and the metal framing layer of the wall
assembly to more effectively account for metal framing conductivity within the envelope. The material properties of
both layers are augmented to account for density, specific heat and thermal mass which allows for the inclusion of
the thermal mass effect when simulated. This method is only applicable to Thermal Bridges created by repetitive
structural members within the envelope assembly. (Baba & Ge, 2015) Although, more effective in calculating clear
field (U O) wall assemblies, the dynamic heat flows which occur at linear transitions and junctions are still ignored
and the point (x) thermal transmittance of attachments outside the sheathing layer of the envelope are also ignored.

Equivalent Wall Method

The equivalent wall method accounts for the dynamic effects of thermal inertia associated with Thermal Bridges
through a combination of steady-state and unsteady-state (dynamic) analysis. The resulting values are defined within
a multilayer wall as assigned values to the corresponding properties layer of the equivalent wall assembly within a
18

whole-building energy simulation model. This equivalency includes calculated values for conductivity, density, and
specific heat. (Martin, Erkoreka, Flores, & Odriozola, 2012) The process for obtaining the different parameter
values for an equivalent wall vary and may include finite numerical analysis, value catalogues, and a variety of
steady-state software calculations. The resulting equivalent wall within the whole-building energy model should
exhibit the thermal behavior of heat flow and inner and outer surface temperature as calculated in the preceding
analysis.

Initial implementation of the method found that direct modeling of complex Thermal Bridges within the whole-
building energy model resulted in greater computer processing requirements and increased complexity. The
reduction of calculation time and complexity prompted the implementation of a simplified layered geometry with
assigned thermal properties for the energy simulation. (Baba & Ge, 2015)

The aim of this methodology is to implement the impact of Thermal Bridges to include their thermal inertia and
simplify data introduction to the whole-building simulation program. The resulting process leverages more detailed
2d steady-state and 3d dynamic state detail simulations to produce thermal wall values which incorporate dynamic
effects. However, the calculation of dynamic thermal properties is more complex than steady-state methods and
requires greater knowledge and expertise.

Direct 2D / 3D Modeling Method

The direct 2D / 3D modeling method requires specialized computer software which integrates 2d steady-state
thermal calculations with whole-building energy analysis. (Baba & Ge, 2015) Typically, this is achieved by
reducing the accuracy of envelope components at the detail level to a layered assembly representation of thermal
boundaries. This layered assembly is more easily translated into the 3d geometry of a whole-building energy
analysis. In 2015, Hua Ge and Fuad Baba investigated the application of the direct 2d / 3d modeling method in
comparison with the equivalent wall and equivalent U-value method. Using WUFI Plus simulation software results
in a cold climatic condition indicated that the annual heating load was underestimated by 13% using the equivalent
U-value method and 9% using the equivalent wall method. Results in a hot climatic condition indicated that the
annual heating load was underestimated by 8% and the cooling load was underestimated by 17% using the
equivalent U-value method and 3% heating and 14% cooling using the equivalent wall method. (Baba & Ge, 2015)

2.1.2 Thermal Interia

In a transient situation, the thermal mass of a building can absorb, store, and progressively release heat depending on
the temperature difference with the immediate surroundings. The amount of heat stored depends on the density ρ
and specific heat capacity c of the material, whereas the rate of heat exchange is influenced by the thermal
conductivity λ of the material. Buildings with a large amount of thermal mass within the thermal envelope, will
display a reduced and delayed reaction to an initial excitation such as a sudden rise in external ambient temperature.
This transient behavior is referred to as the thermal inertia of a building. (Verbeke & Audenaert, 2017) R and U -
value metrics are simplified representations of heat transfer which do not include transient (dynamic) behaviors.
Due to the complexity of calculating dynamic heat transfer and the lack of a simplified approach ASHRAE has
concluded that steady-state calculations are acceptable in cold climates and whole-building energy simulations are
recommended in climates where daily temperature swings oscillate around a comfortable mean. (Verbeke &
Audenaert, 2017) It is the interface with the whole-building energy simulation model which makes the inclusion of
dynamic Thermal Bridges most problematic. An accurate result requires each Thermal Bridge to be characterized
within the simulation model in its dynamic state. (K.Martin, A.Erkoreka, I.Flores, M.Odriozola, & Sala, 2011)

ISO 13786 describes thermal calculation requirements for dynamic conditions defined as periodic, time-dependent
heat transfers. Currently, there are only a few software applications capable of dynamic thermal calculations using
this standard for calculation. (Bruma, Moga, & Moga, 2016) In a whole-building application, the inclusion of
transient functions adds a degree of complexity which makes direct comparison of results with other buildings
problematic. Not only, do the exterior and interior temperature swings need to be identical, but other factors like
natural ventilation, hours of occupied operation, WWR , shading and mechanical/lighting system application can
greatly effect an analysis conducted dynamically. (Verbeke & Audenaert, 2017)
19

2.1.3 Underestimation of Thermal Loads

The construction of any building envelope assembly requires fasteners, fittings and miscellaneous cold-formed
metal fabrications which enable Thermal Bridging conductance. The magnitude of point thermal transmittance on
the overall envelope performance is of specific concern because it is rarely accounted for in whole-building energy
simulation. Given the localized contribution of these bridges, the prevailing focus has been on linear thermal bridges
which are easier to calculate and appear to be responsible for the greatest amount of thermal loss. Calculation of heat
flows through point thermal bridges require finite element analysis and advanced understanding of thermal
conduction and material science. (Theodoros, 2015)

A 2015 study of point thermal bridging effects by Theodoros G. Theodosiou concluded that point thermal bridging
transmissions can have an equivalent or higher effect on an envelopes thermal performance as linear thermal
bridges. The insertion of fasteners directly into the substrate of the wall allows for thermal transfer which is not
mitigated by insulation or air layers in the assembly. Depending on the number of fasteners, material and extent of
associated clips and fittings, the thermal impact of point support attachments can be considerable. (Theodoros, 2015)

2.1.4 2.1.3 Rainscreen Performance

PER and DPR rainscreen assemblies are optimized thermal envelope systems which advantage increased thermal
performance through continuous thermal insulation barriers and improved ventilation and drainage design. Heat
flow studies have indicated the thermal benefits of ventilated systems over conventional sealed cavity walls.
(Sanjuan, Suarez, Gonzolez, Pistano, & Blanco, 2011) The continuous insulation layers which are located on the
exterior face of the sheathing layer mitigate the thermal conduction through structural steel stud framing within the
wall cavity. However, this continuous layer of insulation cannot reduce thermal transmissions for penetrating
elements of high thermal conductance. Studies have shown that heat flows through substrates and fastener
assemblies become more significant as the insulation layer is increased. (Theodoros, 2015) This is important to note
since PER and DPR assemblies are commonly selected for building retrofits due to their advantage when increases
in insulation thickness are prescribed by the building code.

2.1.5 Net-Zero

The reduction of energy load through system optimization is a central tenant of NZEB design. We know from
building codes and regulations that the thermal behavior of the building envelope and its discrete components are of
primary importance. Prescriptive requirements set minimum R and U-values for all envelope components based on
an overall building energy budget. These prescriptive requirements also account for bioclimatic conditions with the
understanding that insulation value is not the preeminent factor in energy efficient design in all climate zones.
Within the 8 ASHRAE climate zones studies have indicated that glazing area and glazing thermal characteristics are
more impactful to annual energy use than the thermal resistance of the opaque wall. (Yong, Kim, & Gim, 2017)
However, the fact that glazing is the weak-link in a buildings thermal envelope is nothing new; we know how to
measure the impacts of glazing performance on a buildings energy efficiency and take corrective or mitigating
action in the design process. We do not know the precise impacts of Thermal Bridges on overall energy efficiency or
have corrective solutions optimized for cost and constructability.
The ability to reach the NZEB goal requires carefully defined and balanced energy demand and thermal efficiency
tradeoffs to be calculated based on annual energy valuations defined by either the site-kBtu or TDV metric. (ARUP,
2012) There are three main characteristics which complicate the calculation of energy demand influenced through
the building envelope : variables that change unsteadily, heat flow associated with non-linear temperature
expressions and different heat transfer mechanisms which interact between them in complex ways. (Martin,
20

Erkoreka, Flores, & Odriozola, 2012) Since, the challenge for NZEB buildings if often one of available space for
on-site renewables, specifically photovoltaic arrays, the reduction of energy load is vital to obtaining a result where
on-site renewables are practicable for a specific project. Thermal conductance through the building envelope must
be understood in its entirety to adequately control and account for annual energy use and on-site renewable
requirement.

2.2 Simulation Software

2.2.1 Flixo Pro®

Flixo Pro® is a computer simulation application that ‘allows realistic calculation of the transient coupled one and
two-dimensional heat and moisture transport in walls and other multi-layer building components exposed to natural
weather’. (Infomind gmbh, 2018)
Flixo Pro® has the ability to approximate the calculation of a 3d equivalent object per ISO 12631.

Calculations based on ISO 10077-2 – 2017 & ISO 10211

Validated per current European standards (EN).

2.2.2 AnTherm®

AnTherm® is a computer simulation application used for the "analysis of thermal behavior of building components
with heat and vapor bridges. It calculates temperature distribution and heat flows and/or vapor diffusion flows in
building structures of arbitrary form and complex material composition - particularly compositions with thermal
bridges”. (Kornicki Services, 2018) It presents critical condensing air humidity (dew point) at all component's
surfaces and shows the distribution of partial vapor pressure in component's interior. This application is also suitable
for analyzing dynamic behavior of building components (for periodic, harmonic, transient boundary conditions).
AnTherm® calculates both steady-state and transient temperature distributions. (Kornicki Services, 2018)

Validated per current European standards (EN).

2.2.3 DesignBuilder®

DesignBuilder® is a building energy modeling (BEM) software tool for simulating energy, lighting and THERMAL
comfort performance. DesignBuilder® calculates a total linear bridging transmittance for each zone by summing the
length for each of the 14 bridging categories and multiplying each by the Psi value entered for that category. The
total bridging length is calculated based on the zone outer dimensions. The total bridging transmittance to outside
for the zone is included in the EnergyPlus® model using a single standard WallExterior surface type per zone with
no film resistance applied. These surfaces are located below the building to avoid interfering with shading
calculations. The area of these fictitious surfaces is calculated such that the total conductance is the same as that of
the sum of the linear bridges based on the known conductance of the predefined construction
called LinearBridgingConstruction. (DesignBuilder Software Ltd, 2018)

Validated per current European standards (EN).

21

2.3 Summary

The referenced material is representative of the bulk of scholarly work related to the process of thermal bridging and
its effects on building performance. A single case study building, and location is the basis for each investigation of
heat flow and energy consumption related to thermal bridging through the building envelope. These investigations
have as a primary focus, calculation methods and verification of simulation results pursuant to overall energy
performance per the specific case study. Thus, the verification of these calculation methods has been properly
established. It is a broader application of these methods to produce a comprehensive result which is now warranted.
A more comprehensive approach which investigates performance outcomes in various climate zones with
perspective baseline mechanical systems would provide an essential overview of the effects of thermal bridging.

The application of steady-state, dynamic-state and whole-building energy modeling simulation has reached the point
where micro, mesa and macro level thermal bridging analysis can be performed with relatively accurate results.
Although, this analysis is dependent on a variety of simulation applications with different approaches and physics
engines, their underlying computation method has been independently tested and validated. It is the application of
thermal bridging within a whole-building energy modeling strategy which requires a greater interface and specific
calculation method within the EnergyPlus (BEM) engine. Thermal bridging input values per junction and type must
have a versatile interface to enable accurate envelope performance results; with specific outputs which articulate
localized thermal influence per these inputs available from the energy model.

22

CHAPTER 3
3. METHODOLOGY

3.1 Introduction
Understanding the loss of building energy through the effects of thermal bridging requires detailed analysis of a
buildings envelope at the micro, meso, and macro scale. Thermal conductivity begins at the detail level of a
buildings design, but it is the position and proliferation of each detail which ultimately effects total building energy
loss. At the micro level, the type, location, and material construction of a detail must be evaluated. At the meso
level, the bio-climatic conditions of the site and the climatic condition set within the building’s interior environment
must be evaluated at the envelope’s interface between exterior and interior environment. At the macro level, the
building envelope must be understood within the context of the buildings mass, orientation and occupancy which
will decide it’s environmental systems and requirements. Thermal bridging analysis is, therefore a multi-step
process where variables must be contemplated and controlled at different scales based on established prerequisites.
The following methodology is established in four stages : Analysis of the construction detail assembly including
material and process selection, analysis of selected detail for thermal bridging value, whole-building energy analysis
to identify the contribution of thermal bridging to total and system energy loss, and analysis of performance toward
optimization for net-zero building design.

Research Questions :
• What is the contribution of thermal bridging to the reduction of envelope thermal resistance
based on common North American rainscreen assembly construction?
• How can thermal bridging be mitigated using select thermal break material applications?
Which materials represent the best value in terms of adaptive applications per designated
detail locations?
• Based on the designated rainscreen assemblies, which application have the best performance
per ASHRAE climate zone based on a contextual NZEB energy model?

23

3.1.1 Methodology Diagram

DESIGNATED ASSEMBLY TYPE
SELECTION AND MATERIAL
PROPERTIES SELECTION
CONSTRUCTION ASSEMBLY CROSS
SECTION DETAIL AT STANDARD
ISO TRANSITION LOCATIONS
ANSI / NFRC 100
EN ISO 10077-2 ; 2017
FASTENER ANALYSIS
SUBFRAME ANALYSIS
MATERIAL ANALYSIS BY LAYER
ANALYSIS RESULTS
Ѳint Interior Temperature
Ѳext Exterior Temperature
Ψk Linear thermal transmittance of linear thermal bridge k
Χj Point thermal transmittance of point thermal bridge j
Hd Direct heat transfer coefficient
Ai Area of element i of the building envelope
Ui Thermal transmittance of element i of the building envelope
lk Length of linear thermal bridge k in meters
λ Design Thermal Conductivity
STANDARD MID-RISE OFFICE
BUILDING CONFIGURATION
WITH APPLICABLE THERMAL
JUNCTIONS FOR ANALYSIS
SIMULATE 8 ASHRAE
CLIMATE ZONES
JUNCTION TYPE INPUT PSI VALUES

ROOF-WALL
WALL-GROUND
WALL-WALL (CORNER)
WALL-FLOOR
LINTEL
SILL
JAMB
ANALYSIS OF PERFORMANCE
IMPROVEMENT TOWARD NET
ZERO
EUI REDUCTION AND REDUCTION
IN POTENTIAL ON-SITE
RENEWABLE (PV)
ASSESS RESULTING ENERGY
PERFORMANCE AGAINST BASELINE
AND INITIAL CONSTRUCTION
ASSEMBLIES
COST / BENEFIT ANALYSIS
APPLY AND REPLACE
MATERIALS WITH LOW
CONDUCTANCE
ALTERNATIVES –
REPEAT ANALYSIS
FROM STEP 1
STEP 3 : CONTEXTUAL ENERGY MODEL ANALYSIS
STEP 2 : THERMAL BRIDGING ANALYSIS
STEP 1 : CONSTRUCTION ASSEMBLY
STEP 4 : OPTIMIZATION AND PERFORMANCE RESULTS
ENERGY PERFORMANCE PER
ASSEMBLY AND CLIMATE ZONE
MEASURED IMPROVEMENT
OVER BASELINE
24

3.1.2 Method of analysis and selected constraints
STEP 1 : Designated Assembly Types
Designated envelope construction assemblies are chosen based on common ‘trade custom and practice’ in the North
American construction market. All assemblies are based on cold-formed metal stud framing, fiberglass mat
sheathing and compliance with NFPA 268 and IBC chapter 14 requirements for exterior walls. The assembly types
designated are pressure equalized rainscreen (PER) and drainage plane rainscreen (DPR) wall types common in the
United States construction market. The selection of insulation types, orientation and performance values within each
assembly are also predicated on common products and code requirements for continuous insulation (c.i.) and overall
wall assembly prescriptive R or U values.

Fig. 3-1 Typical A1 Plan Detail at Junction IW M

STEP 2 : Typical Detail Locations
Typical Thermal Bridging junctions are designated based on the geometry of the contextual energy model and the
designated assembly types. Detail locations are as described in ISO 14683 Annex C and are designated as follows:

Key Description Junction Types in Energy Model
B M Canopy or roof extension Wall / Roof
C M Inside corner Wall-wall (corner)
C N Outside corner Wall-wall (corner)
GF N Ground Floor Wall-Ground Floor
IF N Wall at Internal Floor Wall-floor (not ground floor)
25

IW M Wall at Internal Partition N/A
IW M Roof at Internal Partition N/A
P M Wall at Internal Ceiling N/A
R M Roof Roof - Wall
R N Roof Roof - Wall
W M Window Sill Sill at window
W N Window Jamb / Head Jamb / head at window or door

EW 1 External Wall - Plan Set as assembly U-value w bridging
EW 2 External Wall - Section Set as assembly U-value w bridging
ER 2 External Roof - Section Set as assembly U-value w bridging
EU 1 External Underslab - Section Set as assembly U-value w bridging

Fig 3-2 ISO14683 Commonly Occurring Detail Locations
STEP 3 : Thermal Bridging Analysis
The design details which result from the Designated Assembly Types applied to each junction location are analyzed
using Flixo pro (2D steady-state) and AnTherm (3D dynamic state) simulation software. The distinction between 2D
and 3D analysis is dependent on the geometry of the detail assembly and transition in question. Complex assembly
geometries with hidden or overlapping surface conditions cannot be accurately analyzed in 2D; 3D analysis will be
reserved for specific locations in which 2D analysis cannot accurately capture the construction interface. Final
assembly analysis of all Thermal Bridging detail junctions will result in the following calculated results :
26

• Equivalent U-values – this is a clear field detail analysis which results in an overall assembly U-value
which takes into account the effects of periodic thermal bridges.
• Joint U-values – this is a transitional detail analysis which results in an overall assembly U-value. The
transition occurs between (2) unique constructions i.e. window frame / opaque wall etc.
• PSI – value (2) constructions – this is a transitional detail analysis which results in a Psi-value at the
location of maximum Thermal Bridging. The transition occurs between (2) constructions with assembly
variations i.e. opaque wall / roof, opaque wall / floor, etc.
• PSI – value (3) constructions – this is a transitional detail analysis which results in a Psi-value at the
location of maximum Thermal Bridging. The transition occurs between (3) constructions with assembly
variations i.e. opaque wall / roof / floor, or opaque wall / spacer transition / window frame, etc.
• Mapping of Isotherms and temperature distributions – Isotherm mapping and false color temperature
distributions are generated to indicate heat flow through the detail construction and represent the extent of
conductivity in at the Thermal Bridge.

The following parameters are calculated per designated assembly type :
Ѳ int Interior Temperature
Ѳ ext Exterior Temperature
Ψ k Linear thermal transmittance of linear thermal bridge k
Χ j Point thermal transmittance of point thermal bridge j
H d Direct heat transfer coefficient
A i Area of element i of the building envelope
U i Thermal transmittance of element i of the building envelope
l k Length of linear thermal bridge k in meters
λ Design thermal conductivity
R si Thermal resistance internal surface
R se Thermal resistance external surface

The prescribed method of heat flow analysis as related to the geometric condition described by the junction detail is
based on standard calculation methods set forth by the International Organization for Standardization (ISO). The
ISO has prescribed two methods for calculating heat flow through a building envelope element.

The simplified calculation method is described in ISO 14683 and provides dimensional limits and estimate
accuracy requirements for 2 dimensional simplified calculations to be used when the precise materials and detailing
of the façade has not been developed. This method may be used for preliminary energy and thermal analysis during
early and developmental design phases. Typical junction sections are provided as part of a catalogue with
approximate Y-values. (International Organization for Standardization, 2015)

27

Fig 3-3 Corner Fig 3-4 Interior Floor Fig 3-5 Ground Fig 3-6 Window / Door
The detailed calculation method is described in ISO 10211 and provides dimensional limits and estimate accuracy
for 3 dimensional orthogonal models. This method is more precise in its dimensional accuracy, specifically the
locations of cut-off planes and the extent of construction which is critical to accurate simulation results. Conditions
for simplifying the model or adjusting dimensions and material are tightly controlled. Simplification of geometry or
dimensions for materials with thermal conductivity greater than 3 W/mK is dependent on its relationship with other
materials and their thermal conductivity values.

Fig 3-7 ISO Detailed Calculation Constraints

The requirements for correct calculation of air cavities within elements and assemblies is described in ISO
10077-2 and provides classifications of air cavities and respective heat flow equivalencies per condition. Heat
flow through a cavity occurs simultaneously through convection and radiation. Calculations for convective heat
flow occur in parallel with radiative heat transfer with both calculations dependent on the geometry of the air
cavity under consideration. The calculations differ such that radiative heat transfer is calculated using radiosity
and convective heat flow is calculated using a formula related to equivalent thermal conductivities. Classification
of air cavities is as follows:
• Unventilated air cavities –
28

• Slightly ventilated air cavities – cavities connected to external or internal air by a slit 2mm <10mm with
an assumed surface resistance R S = 0.30 w/m
2
K.
• Well-ventilated air cavities – cavities connected to external or internal air by a slit <10mm with an
assumed surface resistance based on the developed surface and boundary conditions based on Rse = .04
w/m
2
K and Rsi = .13 w/m
2
K.
• Glazing cavities – cavities between glass panes shall be based on ISO 10292

Point thermal transmission (Χ j) is assessed based on calculations described in ISO 10211. This calculation is
required to calculate point thermal transmission at mechanical fasteners and acutely account for the number of
fasteners per square meter. Point thermal transmissions result in equivalent U-values which take into account the
effects of the point transmission of the in-line assembly. (International Organization for Standardization, 2007)
Boundary conditions and boundary surface temperatures are a critical consideration for accurate calculation of
heat flow and temperature distribution through a constructed assembly. Although, location specific environmental
temperatures are the most accurate approach to achieve thermal analysis of a specific building, standard
conditions and requirements provide a better metric for comparative analysis and assessment of thermal
efficiency based on standardized ratings and performance equivalencies. Conventional design values for surface
resistance are require per ISO 6964 and based on horizontal heat flow where surfaces are in contact with an air
layer. The following boundary conditions were selected based on current accepted validated test conditions on the
United States and Europe :

Horizontal Heat Flow
Testing Standard Air Layer Resistance
Requirement
External
Boundary
Ambient Air
Internal
Boundary
Ambient Air
Exterior
Radiation
Thermal
Resistance
of air layer
NFRC 100 Standard -18 °C 21 °C Blackbody N/A
ISO 6964 Standard -10 °C 20 °C Blackbody N/A
ISO 6964 Non-ventilated -10 °C 20 °C Blackbody .40 m
2
K/W
ISO 6964 Ventilated -10 °C 20 °C Blackbody .130 m
2
K/W

Performance values indicated are based on a horizontal heat flow; upward and downward heat flows ±30° from
the horizontal plane alter the heat transfer coefficient values. This should be accounted for in roof and ground
coupled element analysis.
Upwards and Downwards Heat Flow
Testing Standard Air Layer Resistance
Requirement
External
Boundary
Ambient Air
Internal
Boundary
Ambient Air
Exterior
Radiation
Thermal
Resistance
of air layer
ISO 6964 Upwards -10 °C 20 °C Blackbody .10 m
2
K/W
ISO 6964 Downwards -10 °C 20 °C Blackbody .17 m
2
K/W

29

Typical Thermal Bridging Calculation : 2d Steady-State – Simplified Method
Analysis calculation to determine equivalent U-value and Psi – value requires accurate assembly geometry,
material assignment and boundary conditions. Temperature distribution analysis is rendered based on an
isothermal line diagram with color assignments. The isotherm lines connect points of equal temperature; the
space between these lines are then color coded to produce a temperature field. The following examples show heat
flow analysis from detail material assignments in FlixoPro software. Example based on designated assembly type
A1 with applicable materials.

Fig 3-8 Typical Isotherm Temperature Analysis Combined

Fig 3-9 Typical Isotherm over Material Construction and Temperature Field Mapping of Detail
30

Example of Thermal Bridging calculation results per detailed assembly:

Equivalent U-Value calculation
between locations A - B

Equivalent U-Value calculation
between locations E - F

Assembly Psi value calculation

Min / max temperature
calculation and Rsi

Fig 3-10 Typical Results as Simulated

Example of final Thermal Bridging calculation results:

Designated
Assembly
Type
Junction Type Exterior
Panel
Material
Fastener
Material
Ѳext / Ѳint Simulation
Type
U A-B
W/m
2
K
U E-F
W/m
2
K
Ψ A-C
W/mK
R si
m
2
K/W
A1 Clear Field Plan 8.1 St Stl EN 6946 2D .671 .210 - .870
A1 Clear Field Plan 8.1 St Stl NFRC 100 2D .671 .169 - .936
Fig 3-11 Final Results Format

2D steady state analysis allow for point specific (Χ j) Thermal Bridging analysis when reoccurring objects are
identified and their dimensional cross-section and distance to reoccurrence is input into the simulation calculation.
Simulation results for these assemblies does not provide a psi value (Ψ k) since this is not a linear transmittance;
results are provided as an equivalent U-Value for the assembly which considers the thermal effects of the point
transmittance; this is also considered a clear field assembly calculation where applicable to its definition.

31

Typical Thermal Bridging Calculation: 3d dynamic-State
The use of 3d transient-state simulation calculations are required for complex conditions where 2d analysis cannot
accurately assess the complexity of geometry or/and where overlapping layers and assemblies cannot be discerned in
2 dimensions. The consequences of over-simplification of thermal analysis can result in drastic errors and
underestimation of the thermal efficiency of the building envelope. For this reason, specific junction types will be
modeled and calculated in 3d based on the detailed calculation method described in ISO 10211.
Transient analysis evaluates and visualizes heat flows and temperature distributions in building components under
boundary conditions changing in time, periodically. It allows for an analysis of the effects of heat storage in building
construction and their response to changing conditions due to the heat capacity of materials. The transient boundary
conditions are provided as sets of harmonic Fourier coefficients created for respective periodic data. While this
function is useful for site specific simulations, the standardized approach of this research requires comparative
results and analysis between the 2d and 3d simulations sets; for this reason the transient function will not be used in
any 3d analysis.

Fig 3-11 Interior Boundary Analysis Fig 3-12 Exterior Boundary Analysis

Final analysis results using the 3d simulation approach are displayed as a report which designates thermal coupling
coefficients in a matrix format. This matrix is used to calculate Thermal Bridging correction factors including point
thermal transmittance x factor in 3d and linear thermal transmittance Psi factors.

Fig 3-13 Psi Value Determination
32

Use of both 2d and 3d applications allow for a comprehensive analysis of temperature distribution at geometric
surface and sectional assembly conditions. Results will be organized in a tablature format as indicated in Fig 3-11.
Thermal Bridging analysis is an iterative process where assembly, orientation and location of materials may be
revised to reduce thermal transmission. The results of the iterative process are Psi-values for transitional details and
equivalent U-values for clear field wall and roof details. However, the reduction of these does not provide a direct
correlation to annual energy savings via improved building thermal performance. This is due to the overall impact of
each bridge type aggregate to whole building annual energy use. Specific bridges may have a greater impact when
analyzed within the whole-building context. This requires a contextual energy model to measure the effects and
contribution of each bridge type and Psi or X value. (Morrison Hershfield Limited, 2016)
Individual heat flows associated with specific details can be calculated and summed using U o, Ψ o & X o factors. The
results can be summed using the following equation where U T is the total effective assembly thermal transmittance:

Fig 3-14

STEP 4 : Contextual Energy Model
A contextual energy model will be defined based on the Department of Energy’s Commercial Building Reference
Model definition for medium office buildings and ISO 14683, commonly occurring detail locations for thermal
bridges (see fig.3-2). The contextual model design will incorporate the following requirements from each standard :
Department Of Energy Medium Office Building Reference
• 53,628 ft
2
; 4,982 m
2

• 3 floors
• 1.5 aspect ratio
• 13 ft floor-to-floor height ; 3.9 meters
• 9 ft floor-to-ceiling height ; 2.7 meters
• .33 glazing fraction
• 2 elevators
• Baseline HVAC per ASHRAE 90.1-2016 appendix G; simulated per climate zone

ISO 146383 Commonly Occurring Details

• Canopy Projection
• Parapet and Roof Edge
• Inside and Outside Corner Conditions
• Window and Door Sill, Jamb and Head
• Ground and Intermediate Transitions
• Elevated Slab

33

The resulting contextual energy model incorporates the ISO commonly occurring details and the DOE’s medium
office reference model through adjustments in building geometry, fenestration area and façade projections.
Contextual energy performance values based on designated assembly types and calculated Psi values will be
calculated for comparison through a baseline model. The contextual values will aid in understanding how specific
thermal bridge junctions contributed to the overall sum of heat loss through the building envelope.
DesignBuilder® is a building energy simulation program which uses the EnergyPlus® dynamic simulation engine.
As a certified compliance software for UK and the Republic of Ireland, Designbuilder® calculates a total
linear bridging transmittance for each zone by summing the length for each of the 14 bridging categories and
multiplying each by the Psi value entered for that category. The total bridging length is calculated based on the zone
outer dimensions.
Junction Type Description
Roof - Wall Average Psi value
Wall-Ground Floor Average Psi value
Wall-wall (corner) Average Psi value
Wall-floor (not ground floor) Average Psi value
Lintel above window or door Linear transmittance
Sill below window Linear transmittance
Jamb at window or door Linear transmittance

The default Psi values in DesignBuilder® are the based on BRE IP 1/06 values degraded by the greater of 0.04
W/mK or 50%. Metal cladding systems which occur at junctions are of specific concern due to higher heat flow.
Constructions involving metal cladding are roof or wall systems where metal forms an integral part of the
construction, such as metal twin skin systems where the insulation is located between the metal skins and where the
metal skins are typically in the range 0.4 mm to 1.2 mm. Cladding with z-spacers would come into this category as
would composite metal panel systems. If the metal is simply used as an external shield against weather, such as a
rainscreen, this is not classed, for the purposes of calculations as "metal cladding".

Fig 3-15 Designbuilder® Psi Value Dialogue
34

Simulated detailed results include annual energy performance calculated against baseline and the sum of heat gains
into zones from wall, floor and roof inner surfaces.
Layered construction assemblies such as walls and roofs with point thermal transmissions (repeating bridges) must
have the Thermal Bridging values included as an overall assembly U-value.

Fig 3-16 Layered Assembly U-Value with Thermal Bridging

WWR Window-to-wall ratio
Window -to-wall ratio represents the ratio between the net-window and the gross exterior opaque wall area. As the
WWR increases, not only does the amount of glazing increase, but the area of on-site fabricated wall and transitional
junctions per window location decreases, reducing the amount of liner transmittance measured as window jamb,
head and sill. This has implications for the assessment and mitigation of Thermal Bridging. When the WWR
increases to > 50% of the exterior wall, the application and engineering of the glazing assemblies are more likely to
be engineered façade systems like curtainwall, storefront or ribbon window. Performance of the associated wall
system is now part of a pre-engineered, shop-fabricated, engineered-to-order delivery and warranted product
production processes. Thermal performance and bridging at mullion and glazing joint locations is mitigated per the
product fabricator. The methodology required for accurate analysis of Thermal Bridging junctions requires a greater
degree of coordination between product manufacturer and building designer than standard window installations
where the WWR is < 50% and large subdivided glazing areas do not dominate the building envelope.
35

Given that the analysis of factory engineered window systems is not a focus of this research, the contextual energy
model used for performance analysis and comparison is based on a 40% WWR. This will allow for transitions at
window heads, sills and jambs to be calculated per window instance with linear junctions. The 40% WWR limit is
also the maximum vertical fenestration allowed per the base performance rating method detailed in ASHRAE 90.1
and a limit for specific daylighting requirements established in the IECC. (ASHRAE, 2016), (International Code
Council, 2018)
Window-to-wall ratios and R-value for high performance exterior wall enclosure (National Institute of Building
Sciences, 2017)

Fig 3-17
Prescriptive Glazing Requirements
Insulated glazing and laminated glazing assemblies will be used in the contextual model to measure the effects of
each application and associated head, sill, corner and jamb junction thermal transmission. The performance
requirements for this glazing will be as follows :

Product Visible Light
Transmission
UV
Transmission
Solar Energy
Transmission
Winter
U-Value
(W/m
2
K)
Summer
U-Value
(W/m
2
K)
Solar Heat
Gain
Coefficient
Light-
to-
Solar
Gain
1” IGU *
56% 22% 26% .29 (1.65) .27 (1.6) .29 1.96
13/16” Lam **
84% - 59% .84 (5.2) .92 (4.8) .69 -

* The 1” IGU (Insulated Glass Unit) consist of : ¼” thick outboard lite , ½” air gap , ¼” thick inboard lite.
* * The 13/16” laminated glass lite consist of : 3/8” thick outboard lite, .060 PVB interlayer, 3/8” thick inboard lite.
Standard surface exchange coefficients shall be simulated based on H e = 23 W/m
2
K and H i = 8 W/m
2
K
36

Contextual Model Elevations

Fig. 3-18 Elevation East – 40% WWR Fig. 3-19 Elevation East – 40% WWR

Fig. 3-20 Elevation North – 40% WWR

Fig. 3-21 Elevation South – 40%WWR

37

Contextual Model Simulation Baseline
ASHRAE 90.1-2016 establishes requirements for baseline building simulations during early design when the actual
mechanical, electrical and plumbing systems are not known. These requirements for baseline simulations are
specified per ASHRAE climate zone and building occupancy classification and will be used for the baseline and
comparative simulations. These include the following :
• All conditioned spaces must be simulated as being cooled and heated with 15 ft high thermal zones and air
leakage set to 0.4 cfm/ft
2

• Infiltration ACH rates shall be calculated per formula (I AGW) as a function of above grade walls.
• HVAC system in climate zones 3B, 3C and 4-8 shall be packaged VAV with reheat
• HVAC system in climate zone 0-3A shall be VAV with PFP boxes
• Heating control set point shall be set to 50
o
F for all hours
• Economizers included for comfort cooling per climate zone as established per ASHRAE baseline
• Economizer high-limit shut-off temperature shall be 70
o
F or 75
o
F per climate zone as required
• Service water heating shall be electric resistance storage heater
• Lighting shall be 50fc; Exterior Lighting shall be 900W Zone 4.
In addition to these ASHRAE 90.1-2016 requirements, building operation schedule and requirements specific to a
medium size office building will be simulated as follows :
• Computer heat gains shall be set at 10.8 W/m
2
based on the use of desktop office computers
• Office equipment gains shall be set at 11.77 W/m
2

• Occupancy density shall be set to .1110 people / m
2

• Weekday schedule shall be 5 days (7a.m. – 7p.m.)
• 5 Holidays will be accounted for in the annual schedule
• Saturday’s will be scheduled
These and all other required inputs required for a whole-building energy simulation will be based on ASHRAE 90.1-
2016.
Contextual Model Simulation Climate Zone and Reference City
ASHRAE Climate
Zone
Test City HDD CDD Winter Design
Dry-Bulb
o
F
Summer Design
Wet-Bulb
o
F
1A Miami, Florida 200 9474 50.5 78.7
2A Houston, Texas 1371 7357 35.1 79.3
3B Los Angeles, California 1458 5281 46.1 67.9
4A Baltimore, Maryland 4707 3709 16.7 75.6
5A Chicago, Illinois 6536 2941 0.8 74.3
6A Minneapolis, Minnesota 7981 2680 -9.4 72.7
7 Duluth, Minnesota 9818 1536 -15.1 67.6
8 Fairbanks, Alaska 13940 1040 -39.9 59.9
U.S. Department of Energy – energy.gov

38

Contextual Model Envelope Inputs
The contextual energy model will have two versions – baseline and thermally bridge. The baseline version will
consist of envelope assembly values based on material layered constructions created from the library in
DesignBuilder®. The correct thickness and material properties will be used in each layered assembly and
DesignBuilder® will calculate the overall U-value. The thermally bridged version will consist of envelope
assemblies which represent the equivalent U-value as calculated in Flixo Pro® which includes the effects of point
and linear thermal bridging on the resistance of the assembly. Additionally, Psi values for each junction will be input
into DesignBuilder® based on the linear transmittance calculations derived from Flixo Pro®. Thus, in-line and
linear junction assemblies will be accounted for in the contextual model simulation. Where multiple details with
different Psi values occur at the same junction, a weighted Psi value will be calculated based on the total length of
the junction as defined in DesignBuilder®.

Simulation and Calculation Restrictions and Obstacles
EnergyPlus® does not currently have the capacity to calculate repeating Thermal Bridges in its simulation engine.
DesignBuilder® provides a work-around for this limitation by using adjusted U-values for the assembly. A
corrected U-value can be calculated and entered into the energy program as U corr which accounts for the effects of
thermal bridging; this typically requires that the insulation layer of the assembly must be revised to represent the
corrected value. (Engineers, 2015) The corrected value approach will be used to input the equivalent U-values as
simulated in Flixo Pro®. These values tend to be higher than those calculated in DesignBuilder® using its
‘thermally bridged’ function. The point thermal transmission created by roof drains and rooftop requirement pads
will be excluded from the simulations. These are difficult to adapt to the energy model, and a corrective factor
would be too speculative.

Ucorr = Uo + [Σ(Ψi * Li) + Σ(χj * nj)]/A

Designated
Assembly Type
DesignBuilder®
Calculated U-Value per Layer
W/m
2
K
Flixo Pro®
Equivalent U-Value with Thermal Bridge
W/m
2
K
A1.1 .150 .701
A2 .314 .620
A3 .233 .488
U-values as calculated in each perspective software

39

STEP 5 : Comparison and Conclusions
Final data comparisons and conclusion will be based on performance improvements towards net-zero
annual energy efficiency. A cost benefit analysis will be based on a comparison of increased construction
costs associated with each mitigation approach and the net positive energy efficiency gained from that
approach toward net-zero efficiency and renewable on-site requirements.
BL = Baseline simulation model per ASHRAE 90.1-2016
A1.1 = Thermal Bridging values per designated assembly A1.1
Delta = Calculated change in performance between baseline and designated assembly as a percentage

SIMULATION
SUBFRAME ASSEMBLY
TOTAL SITE ENERGY
(kWh)
TOTAL SOURCE ENERGY
(kWh)
HEATING (kWh)
COOLING (kWh)
EXTERIOR LGHTING (kWh)
INTERIOR LGHTING (kWh)
INTERIOR EQUIP (kWh)
WATER SYSTEMS (kWh)
EUI (Kbtu/ft
2
)
OPAQUE INT SURFACE
SENSIBLE HEAT GAIN (GJ)

BL RNSCN 833,145.0 2,822,477.0 389,892.0 1593.0 3898.0 55,214.0 352,864.0 29,682.0 180 104.3
A1.1 ACRIC 1,055,106.0 3,621,819.0 603,215.0 1209.0 3898.0 53,636.0 362,643.0 30,505.0 230 25.0
Δ
- + 27% +28% +55% -24% 0% -3% +3% +3% +28% -76%

Renewable Energy Benchmarks for NZEB Evaluation
The type and extent of photovoltaic panel arrays is a determining limitation which must be considered in
any NZEB design analysis. Based on the contextual model occupancy classification and designated
HVAC system, an allowable PV array area of 60% of the roof surface is feasible and will be estimated as
a renewable benchmark. This is equivalent to a 12,000 ft
2
(1115m
2
) roof area dedicated to a PV array on
the primary roof surface.
Based on a standard fixed photovoltaic system with 14% system loss and 96% inverter efficiency annual
energy production at the optimal tilt angle is estimated as follows:
• Miami Fla : 244,000 kWh/yr
• Houston Tx : 244,000 kWh/yr
• Los Angeles Ca : 267,000 kWh/yr
• Chicago Il : 217,000 kWh/yr
• Baltimore Md : 226,000 kWh/yr
• Minneapolis Mn : 233,000 kWh/yr
• Duluth Mn : 222,000 kWh/yr
• Fairbanks Ak : 166,000 kWh/yr
40

3.1.3 Designated Assembly Types
A1 : Typical Ventilated Rainscreen Wall Assembly

Fig. 3-21

NO. MATERIAL / COMPONENT CONDUCTIVITY
W/m
2
K - U
DESIGN
THERMAL
CONDUCTIVITY
W/mK - λ
DENSITY
kg/m
3
-

ρ
SPECIFIC
HEAT
CAPACITY
J/kgK Cρ
1 5/8” gypsum wallboard .19 707.18 1150
2 6” 33 mil steel stud framing .33 7850 450
3 3 ½” fiberglass batt insulation .035 12 1030
4 5/8” thick fiberglass matt gypsum sheathing .19 617.13 1150
5 .4mm HDPE Air and weather barrier membrane .49 96.5 1800
- 1mm Polyethylene-asphaltic flashing membrane .49 96.5 1800
6 2” mineral fiber board insulation (c.i.) .023 70 870
7.1 8mm stainless steel hex head fastener (alum to steel) 17 7900 500
Aluminum subframe attachment clip 160 2800 880
Aluminum subframe vertical angle 160 2800 880
Aluminum interlocking channel frame rail 160 2800 880
7.2* Galvanized Steel Z-girt .33 7850 450
7.3* 2” Pultruded Fiberglass Clip .40 1900 700
Galvanized steel vertical angle .33 7850 450
7.4* Pultruded fiberglass Girt (continuous extrusion) .40 1900 700
- 1” Ventilation Cavity .025 1.23 1008
8 SERIES PANEL MATERIAL OPTIONS
8.1 Fibre cement panel .56 1900
41

Total Assembly U-Value per Layer .150
8.2 Phenolic panel (HPL) .30 1300 1700
8.2 Terracotta panel 1.0 2000 800
8.4 4mm Alum Composite (polyethylene core) panel 18 18 11000
* Subframe components per assembly : 7.1-A1.1, 7.1-A1.2, 7.3-A1.3, 7.4-A1.4

A2 : Typical Drainage Plane Rainscreen Wall Assembly

Fig. 3-22

NO. MATERIAL / COMPONENT CONDUCTIVITY
W/m
2
K - U
DESIGN
THERMAL
CONDUCTIVITY
W/mK - λ
DENSITY
kg/m
3
-

ρ
SPECIFIC
HEAT
CAPACITY
J/kgK Cρ
1 5/8” gypsum wallboard .19 707.18 1150
2 6” 33 mil steel stud framing .33 7850 450
3 3 ½” fiberglass batt insulation .035 12 1030
4 5/8” thick fiberglass matt gypsum sheathing .19 617.13 1150
5 .4mm HDPE Air and weather barrier membrane .49 96.5 1800
6 3/16” rainscreen drainage mat – polystyrene
corrugated sheets
.16 1050 1300
7 2” XPS insulation (c.i.) .022 28
8 2.5lbs/yd expanded galvanized metal lath – self
furred ¼” minimum
.41 840 1200
9.1 Anchor plate
9.2 SD zinc screw .33 7850 450
10 SERIES PANEL MATERIAL OPTIONS
10.1 3-part architectural plaster 1.00 1000
Total Assembly U-Value per Layer .314
42

10.2 Adhered brick veneer .80 1890 880
10.3 Adhered stone tile 1.2 2000 840

A3 : Typical Face Brick Veneer Ventilated Rainscreen Wall Assembly

Fig. 3-23

NO. MATERIAL / COMPONENT CONDUCTIVITY
W/m
2
K - U
DESIGN
THERMAL
CONDUCTIVITY
W/mK - λ
DENSITY
kg/m
3
-

ρ
SPECIFIC
HEAT
CAPACITY
J/kgK Cρ
1 5/8” gypsum wallboard .19 707.18 1150
2 6” 33 mil steel stud framing .33 7850 450
3 3 ½” fiberglass batt insulation .035 12 1030
4 5/8” thick fiberglass matt gypsum sheathing .19 617.13 1150
5 .4mm HDPE Air and weather barrier membrane .49 96.5 1800
6 2” XPS insulation (c.i.) .022 28
7.1 Fleming 22 gauge pre-galvanized steel channel .33 7850 450
7.2 #10 galvanized TEK screw fastener .33 7850 450
7.3 Fleming 22 gauge pre-galvanized steel strip .33 7850 450
7.4 Reinforcing wire tie .33 450
8 3 5/8” thick full brick * .82 1760 800
9 Pointing mortar .88 2800 896
43

Total Assembly U-Value per Layer .233
(International Organization of Standardization, 2007)
*density and conductivity values may change per brick manufacturer.

3.1.4 Typical Detail Locations

Refer to STEP 2 : Typical Detail Locations for additional information regarding the designation and organization of
typical detail locations. The following locations are based on the contextual model design and construction per
assemblies A1, A2 and A3.

Fig 3-25 Contextual Model Axonometric

Fig 3-25 Detail Locations
44

CHAPTER 4a

4a. PRESSURE EQUALIZED RAINSCREEN ANALYSIS

4a.1 Introduction
Pressure Equilized Rainscreen (PER) Assemblies are characterized by spatial compartmentation which
utilize a drainage or ventilation cavity to create a more effective weather barrier. (Metal Construction
Association, 2006) Material thermal transfer through the assembly is most dynamic within this cavity and
the elements it contains. The ventilation cavity of the PER occurs on the exterior side of the primary
sheathing layer and is comprised of an air and weather membrane, a metal subframe which offsets the
façade panels from the sheathing layer and creates the cavity, a continuous insulation (c.i.) layer and the
exterior façade panels. These elements all exist within the exterior thermal environment of the building
and contribute to thermal transfer through the numerous fastener attachments which connect them and
connect through the sheathing layer to the interior environment. An understanding of how these elements
and their materials thermal conduction influence the overall performance of the building envelope is
critical to the employ of an effective strategy to reduce thermal transfer.

Fig 4a-1 PER Assembly Diagram

All of the following simulations will be based on clear-field assemblies and use the simplified method.

45

4a.1.1 Contribution of air and weather barrier system to mitigation of heat transfer thru a PER
assembly fastener attachment.
Air and weather barrier systems are designed to control the flow of air and the infiltration of water
through the building envelope and mitigate air leakage between conditioned interior air and the exterior
environment. ASHRAE 90.1 describes these systems as continuous air barriers and sets requirements and
conditions for installation and air permeance. (ASHRAE, 2016) There is a distinction between air
barriers, vapor barriers and weather barrier systems which is based on the permeance of the material and
integration with specific exterior wall construction assemblies. PER applications employ WBR (weather
barrier systems) which control air infiltration and act as the primary water-resistant membrane applied at
the face of the exterior sheathing.
These systems are not designed to mitigate material thermal conduction; however, they are formulated
from materials which may be classified as a thermal break. The WBR system membranes tested have a
thermal conductivity of .49 W/mK which is just below the .52 W/mK maximum value parameter which
defines a material as a thermal break by the NFRC. (National Fenestration Rating Council, 2013)
The WBR membrane is a formulation of HDPE high-density polyethylene specific to each manufacturer.
The membrane is available as a fluid applied, sheet applied or self-adhered product with an applied
thickness of .4mm. In addition to the primary membrane, there is an additional flashing, or detail
membrane which is 1mm thick. This flashing membrane is applied at transitional conditions like
openings, terminations, and movement joints.
Φparallel : Heat Transfer through the assembly
Uequiv : Equivalent U value of assembly including repeating element K factor

Table 4a-1
ASSEMBLY WBR
Ѳ ext / Ѳ int U EQUIV
W/m
2

Ψ CONST
W/mK
Φ PARALLEL
W/m
Delta
% of U EQUIV
A1 NONE
EN 6946
.688 .280 .1 BASELINE
A1 .4mm HDPE WEATHER
BARRIER MEMBRANE
EN 6946
.675 .247 .2 1.9
A1 1mm HDPE SA FLASHING
MEMRANE
EN 6946
.689 .201 .3 1.3

*design thermal conductivity values and product thickness based on Grace Perma-barrier products.

46

Fig 4a-2 HDPE Barrier Simulation

4a.1.2 Contribution of exterior façade panel material to heat transfer thru a PER assembly
subframe.
Exterior PER façade panels constitute the secondary weather barrier of the assembly and are available in
various materials and thicknesses per structural requirements. Within the context of the EN 6946
simulation parameters, the exterior panel material is exposed to an exterior air temperature of -10°C and
may contribute to thermal conduction from the building interior through the subframe and fasteners.
However, given the subframes location and connection to the same exterior air temperature it is unclear if
the exterior panels material has a significant effect on the thermal conductivity of the PER assembly.
Table 4a-2
ASSEMBLY FAÇADE PNL
DESCRIPTION
PNL
THICKNESS
- mm
DESIGN
THERMAL
CONDUCTIVITY
W/mK - λ
Ѳext /
Ѳint
U equiv
W/m
2
K
Ψ A-C
W/mK
R si
m
2
K/W
Φ parallel
W/m
Delta
% of
UEQUIV
A1 8.1 - FIBRE
CEMENT
8 .56 EN
6946
.685 .199 .886 .303 - 2.14
A1 8.2 -
PHENOLIC
8 .30 EN
6946
.690 .200 .913 .218 - 1.43
A1 8.3 -
TERRACOTTA
4 1 EN
6946
.650 .135 .913 .150 - 7.14
A1 8.4 - ALUM
COMPOSITE
MTL
4 18 EN
6946
.700 .204 .888 .106 BASELINE

47

4a.1.3 Aluminum vs Galvanized Steel Subframe Analysis

The subframe of a PER assembly consists of metal framing elements which form the ventilation cavity of
the rainscreen by creating an offset between the sheathing and primary WBR and the exterior façade
panel. This offset is typically formed by (2) layers of metal framing members which intercross vertically
and horizontally. The intercrossing of the members allow for adjustment and adaptation when affixing
exterior façade panels of different sizes.
The Z-Girt subframe is fabricated using standard continuous galvanized steel Z-girt (z-furring) in 16ga or
18 ga thicknesses. These are available in vented, non-vented or notched varieties with facilitate drainage
within the cavity. Application of Z-Girt framing requires the same application specific engineering as
other light-gauge structural framing. The thermal conductivity if this system is dependent on the
continuous nature of the framing against the sheathing layer and the material properties of the framing
members.
The Aluminum Clip, Rail and Interlocking Channel (ACRIC) subframe is a pre-engineered attachment
system which is tested for code compliance and engineered per panel type and application. As a pre-
engineered product, this system has the benefit of design and engineering consultant services offered by
the manufacturer to the consumer. The thermal conductivity of this system is dependent on the clip
interface with the sheathing layer and the material properties of the framing members.

Fig 4a-3 Z-Girt Subframe Assembly Fig 4a-4 Alum Clip, Rail and Channel Subframe Assembly

48

All assemblies tested with 10mm thick Fibre Cement Panel and zinc coated steel fasteners.
Table 4a-3
ASSEMBLY SUBFRAME
DESCRIPTION
SUBFRA
ME
MEMBER
SUBFRAMEMATER
IAL
Ѳext / Ѳint UEQUIV
W/m
2
K
ΦPARALLEL
W/m
Delta
% of UEQUIV
A1 CONTINUOUS Z-GIRT GALV STEEL
EN 6946
.579 1.020 BASELINE
A1 NON-CONT* Z-GIRT GALV STEEL
EN 6946
.562 .478 + 2.9
A1 CONTINUOUS Z-GIRT ALUMINUM
EN 6946
.623 .976 -7.6
A1 CONTINUOUS Z-GIRT ST STEEL
EN 6946
.469 .408 + 18.9
A1 NON-
CONTINUOUS
CLIP
ACRIC ALUM
EN 6946
.701 .154 - 21.1

*Non-Continuous Z-Girt assumes a 6” section of Z-Grit spaced 48” o.c.

Fig 4a-5 Continuous Z-Girt vs Alum Clip, Rail and Channel Subframe Assembly

4a.1.4 Fastener Material Analysis
The PER subframe is attached through the WBR membrane and sheathing layer to a cold-formed steel
stud via a hex head screw fastener. These fasteners are typically 8mm (#10) Tech Screw with 5/16” head
w self-sealing washer and are available in Stainless Steel (austenitic) or steel with zinc coating. Given the
49

difference in the thermal conductivity of stainless steel (17 W/mK) and zinc coated steel (50 W/mK) these
penetrations could have a significant effect on thermal conductivity through the envelope.
Q FASTENER : Heat flux measured at the head of fastener
Table 4a-4
ASMBLY FASTENER
TYPE
FASTENER
MATERIAL
FASTENERS
PER CLIP
DESIGN
THERMAL
CONDUCTIVITY
W/mK - λ
Ѳext / Ѳint UEQUIV
W/m
2
K
QFAST
W/m
2
K
ΦPARALLEL
W/m
A1 - PLAN 8mm HEX
HEAD
GALV STL 2 50
EN 6946
.583 379.0 .910
A1 - PLAN 8mm HEX
HEAD
ST STL 2 17
EN 6946
.573 197.9 1.452
A1 - PLAN 8mm HEX
HEAD
GALV STL 2 50
EN 6946
.703 385.4 .360
A1 - PLAN 8mm HEX
HEAD
ST STL 2 17
EN 6946
.687 185.9 .280

2.3% improvement in U EQUIV using stainless steel fastener attachments

Fig 4a-6 Stainless Steel vs Zinc Coated Steel Fastener Analysis

50

4a.1.5 Material Mitigation Analysis
The PER subframe is the primary element in the assembly that assists in thermal transfer through the
assembly. Application of thermal break materials can reduce this transfer but the amount of mitigation
would be dependent on the material and thickness of the thermal break material. (National Fenestration
Rating Council, 2013) Four common materials used for thermal breaks with lambda values ranging from
.49 to .17 will be tested in various thickness and configuration to access performance improvement over
an assembly with no mitigation.
Φ PARALLEL : Heat flow measure across assembly thru subframe at attachment
All assemblies tested with 10mm thick Fibre Cement Panel, zinc coated steel fasteners and aluminum
ACRIC subframe.
Table 4a-5
ASMBLY SPACER
MATERIAL
SPACER
THICKNESS
(INCHES)
DESIGN
THERMAL
CONDUCTIVITY
W/mK - λ
Ѳext / Ѳint U EQUIV
W/m
2
K
Ψ CLIP
W/mK
Φ PARALLEL
W/m
Delta
% of U EQUIV
A1 - PLAN NONE NONE -
EN 6946
.705 .208 .239 BASELINE
A1 - PLAN HDPE .125 .49
EN 6946
.703 .206 .026 .28
A1 - PLAN HDPE .25 .49
EN 6946
.701 .201 .128 .57
A1 - PLAN FIBERGLASS
PULTRUDED
.125 .40
EN 6946
.704 .206 .167 .14
A1 - PLAN FIBERGLASS
PULTRUDED
.25 .40
EN 6946
.701 .201 .051 .57
A1 - PLAN FIBERGLASS
PULTRUDED
FULL CLIP .40
EN 6946
.418 .177 .005 40.7
A1 - PLAN POLYMIDE .125 .25
EN 6946
.703 .205 .311 .28
A1 - PLAN POLYMIDE .25 .25
EN 6946
.699 .201 .014 .85
A1 - PLAN PVC .125 .17
EN 6946
.702 .205 .139 .43
A1 - PLAN PVC .25 .17
EN 6946
.698 .201 .102 .99
A1 - PLAN PVC FULL CLIP .17
EN 6946
.344 .062 .107 51.2

U-value of .7 = R-value of 1.4
U-value of .5 = R-value of 2.0
U-value of .4 = R-value of 2.5
U-value of .3 = R-value of 3.3

51

4a-7 Subframe Mitigation via Spacer 4a-8 Subframe Mitigation via Fiberglass Clip

4a.2 Results Summary
Contribution of air and weather barrier system to mitigation of heat transfer thru a PER assembly fastener
attachment.
Simulation analysis indicates that the application of an HDPE air and weather barrier system has a
marginal effect on thermal transfer through a typical fastener penetration in PER assemblies. At .4mm
and 1mm thick the installed membrane system is too thin to mitigate thermal transfer in any amount
which could decrease the equivalent U-value of the assembly and increase thermal performance of the
exterior envelope. The effectiveness of the .4mm primary membrane is insignificant in terms of thermal
improvement. The effectiveness of the 1mm self-adhered flashing membrane translates to a 1%
improvement in the equivalent U-value of the assembly.

Contribution of exterior façade panel material to heat transfer thru a PER assembly subframe.
The contribution of the exterior façade panel is dependent on the materials conduction value, thickness
and number of attachment points to the subframe. The aluminum composite panel was chosen as the
baseline for performance measurement due to the higher thermal conductivity value of the material. It
should also be noted that the effects of solar heat gain (SHGC) we not factored into the assessment of the
panels. Simulation analysis indicates that the panels material and thickness does have an effect on thermal
conduction through the subframe, even though the subframe is also exposed to the same exterior
environmental temperature. However, the effect on the equivalent U-value of the overall wall assembly
was marginal. For example, the difference between the U EQUIV of the aluminum panel vs the terracotta
panel translates to respective R-values of 1.4 and 1.5; this difference is not substantial enough to ascribe
the panel material as a potential mitigation factor for consideration in the design process.
52

Aluminum vs Galvanized Steel Subframe Analysis
Simulation analysis indicates that the thermal conduction through the subframe can have a significant
impact on the equivalent U-value of the overall wall assembly. Specifically, the choice of a standard Z-
girt framing over an engineered-to-order ACRIC subframe system can affect thermal transfer from 14%-
50% depending on the material chosen for the Z-girt. Additionally, the performance difference between a
continuous frame and a non-continuous clip is marginal. The relation between the subframe and fastener
attachment / penetration is the significant point of thermal transfer; the continuity of the subframe outside
the sheathing layer is not thermally significant. The continuous Z-girt requires fewer fasteners in
comparison with the vertical clip systems. Clips require (2) fasteners per clip to eliminate rotation while
the continuous Z-girt is not susceptible to rotation and can be applied with a single fastener repeated at a
fixed distance per structural calculation.
Fastener Material Analysis
Simulation analysis indicates that the choice of stainless steel or galvanized steel fastener has a marginal
impact on the thermal transfer through the assembly. This analysis is further evidence that the choice of
subframe system and material is more significant to thermal performance of the envelope assembly.
Material Mitigation Analysis
Simulation analysis indicates that the application of a thermal break material at the point of fastener
penetration has a marginal effect on thermal transfer if that material is < .25” in thickness. Heat flux
through the fastener is primarily accelerated via the clip material through the fastener. Placement of a
low-conductivity material behind the clip with the fastener penetrating through its material does reduce
heat flux, but only marginally reduces the equivalent U-value of the wall. When the entirety of the
subframe or clip attachment is fabricated as a thermal break the mitigation of thermal transfer can be
significant. Improvements in thermal resistance range from 43% to 135% depending on the lambda value
of the material used to form the subframe attachment. However, this improvement is specific to
conditions of clear-field assembly and do not necessarily correlate to linear thermal transitions. These
transitions may reduce the level of improvement depending on length, number and corresponding psi-
value.

53

CHAPTER 4b
4b. THERMAL BRIDGING ANALYSIS PER DETAIL LOCATION

4b.1 Introduction
Psi (Ψ) value calculations are required for an accurate building energy analysis which includes the effect of linear
thermal transmittance (y-value). Calculation of heat transfer through envelope construction requires prescribed
analysis at the micro level of detail. The following analysis calculates equivalent U-value and Psi value thermal
transmission to obtain accurate inputs for the contextual building energy model simulation. The transmission heat
loss coefficient (H TB) is calculated based on the total length of condition per the contextual building model.
Steady-state simulations of accurate 2d architectural details are used to provide accurate in-line and transitional
junction input values. The architectural details are based on common construction techniques, configurations, and
material applications in the United States construction market. In specific cases, mitigation strategies involving SPF
insulation applications were also tested to document the potential for thermal transfer reduction.
Detail and junction locations are further defined in Chapter 3.

Fig 4b-1 Detail Locations
54

4b.1.1 Typical Exterior Wall Assembly Analysis – Clear Field
Typical wall assemblies are based on clear-field conditions with cold-formed steel stud framing at 16” o.c. Thermal
analysis of the assembly includes periodic fastener and metal framing supports as spaced in the typical wall
construction conditions.
Detail Location : EW 1
Analysis : Heat loss through area – U-value with periodic thermal bridge – simplified method.
Table 4b-1
ASSEMBLY - LOCATION SUBFRAME
Ѳext / Ѳint UEQUIV
W/m
2
K
REQUIV
m
2-
K/W
REQUIV
ft
2
Fh/Btu
UPARALLEL
W/m
2
K
A1 TYPICAL WALL PLAN – EW 1 ACRIC
EN 6946
.701 1.425 8.1 .154
A1 TYPICAL WALL PLAN – EW 1 GALV
EN 6946
.562 1.782 10.1 .478
A1 TYPICAL WALL PLAN – EW 1 FIBERGLASS
EN 6946
.418 2.392 13.6 .177

A2 TYPICAL WALL PLAN – EW 1 NONE
EN 6946
.620 1.613 9.2 .219
A3 TYPICAL WALL PLAN – EW 1 NONE
EN 6946
.488 2.047 11.6 .217

4b.1.2 Roof Assembly Analysis
Roof assemblies represent an important part of a buildings thermal envelope system. Thermal transfer
through a roof assembly is dependent on a number of factors, however the effects of thermal bridging are
primarily associated with conductive material penetrations. In commercial building construction these
penetrations can be numerous and expansive depending on the building use and location. Common
penetrations include roof drains, vents, supports for mechanical equipment, mechanical screens, signage,
telecommunication arrays and photovoltaic panel arrays. Numerous penetrations can have a culminative
effect, degrading the thermal resistance of the overall roof assembly.
The analysis conducted is based on common penetrations related to mid-size office buildings. The
primary roof assembly consists of the following :
• PVC roof membrane
• ½” thick fiberglass matt protection board
• 5” thick Polyisocyanurate roof insulation (PIR)
• Composite corrugated metal deck with concrete fill (4.5” thick)
• Spray-applied fireproofing at beams
• Closed-cell SPF insulation used at the underside of deck to mitigate thermal bridging (2” thick)
55

Roof assemblies which include a suspended interior ceiling, forming the boundary between conditioned
and unconditioned space, will demonstrate increased thermal performance when compared with a
conditioned space which is open to the underside of the structural roof deck. This is due to the thermal
resistance offered by the cavity air space between ceiling and structural roof deck.
Roof Assembly : Clear Field
Detail Location : ER 1 and ER 2
Analysis : Heat loss through area – U-value with periodic thermal bridge – simplified method. In this
instance, structural framing members may be analyzed as periodic, repeating thermal bridges.
Table 4b-2
ASSEMBLY - LOCATION CEILING SPF
Ѳext / Ѳint UEQUIV
W/m
2
K
UPARALLEL
W/m
2
K
ΨBEAM
W/mK
Delta
% of
U EQUIV
ROOF ASSEMBLY – ER 1 YES 20” CAVITY NO
EN 6946
.167 .169 - BASELINE
ROOF ASSEMBLY – ER 1 NO NO
EN 6946
.174 .173 - - 43.1
BEAM AND INTERIOR PARTITION CONNECTION
ROOF ASSEMBLY W BEAM / PTN – ER 2 YES 20” CAVITY NO
EN 6946
.166 .168 .004 - 0.59
ROOF ASSEMBLY W BEAM / PTN – ER 2 NO NO
EN 6946
.068 .036 .071 - 59.2

Roof Assembly : Concrete equipment pad penetration and SPF insulation mitigation
Detail Location : ER 3 and ER 4
Pad A : 14” X 14” reinforced concrete pad - R 3
Pad B : 5’-0” X 8’-0” reinforced concrete pad - R 4
Closed cell spray polyurethane foam insulation (SPF) at 4” thick applied to underside of structural roof
deck below concrete pad : λ = .025 W/mK
Analysis : Heat loss through area – U-value with periodic thermal bridge – simplified method
Table 4b-3
ASSEMBLY - LOCATION CEILING SPF Ѳext / Ѳint UEQUIV
W/m
2
K
UPARALLEL
W/m
2
K
ΨBEAM
W/mK
Delta
% of
UEQUIV
ROOF ASSEMBLY – ER 1 YES 20” CAVITY NO EN 6946 .167 .169 - BASELINE
ROOF ASSEMBLY W PAD A – ER 3 YES 20” CAVITY NO EN 6946 .834 .168 1.47 - 400
ROOF ASSEMBLY W PAD A – ER 3 YES 20” CAVITY YES EN 6946 .717 .168 1.21 - 330
56

ROOF ASSEMBLY W PAD B – ER 4 YES 20” CAVITY NO EN 6946 1.80 2.14 .875 - 978
ROOF ASSEMBLY W PAD B – ER 4 YES 20” CAVITY YES EN 6946 .928 .199 1.61 - 456

Roof Assembly : Typical Drain Penetration
Detail Location : ER 5
Cast-iron roof drain : 15” Ø
Closed cell spray polyurethane foam insulation (SPF) at 4” thick applied to underside of structural roof
deck at location of drain penetration : λ = .025 W/mK

Analysis : Heat loss through area – U-value with periodic thermal bridge – simplified method
Table 4b-4
ASSEMBLY - LOCATION CEILING SPF
Ѳext / Ѳint UEQUIV
W/m
2
K
UPARALLEL
W/m
2
K
ΨA-C
W/mK
Delta
% of
U EQUIV
ROOF ASSEMBLY – ER 1 YES 20” CAVITY NO
EN 6946
.167 .169 - BASELINE
DRAIN PENETRATION – ER 5 YES 20” CAVITY NO
EN 6946
1.22 .322 - -630
DRAIN PENETRATION – ER 5 YES 20” CAVITY YES
EN 6946
.862 .108 - - 416

4b.1.3 Elevated Building Structure Analysis (Underside of Structure)
Detail Location : EU 1, EU 2 and EU 3
Building structures which are suspended above the ground plane by cantilever, column or bearing wall are
becoming more common in contemporary architectural design. The Thermal performance of the building
envelope in these conditions is different than that of a roof assembly. Although, the underside of structure
is exposed to the exterior air temperature it is not directly exposed to solar radiation, or rainfall. Given
that occupied conditioned space is suspended in an atmospheric condition, the thermal transfer through
the structural frame and deck should be addressed with insulation.
Closed cell spray polyurethane foam insulation (SPF) at 4” thick applied to underside of suspended
structural deck : λ = .025 W/mK

Analysis : Heat loss through area – U-value with periodic thermal bridge with exception – simplified
method. Continuous structural beams can also be assessed as a linear thermal bridge
57

Table 4b-5
ASSEMBLY - LOCATION SPF
Ѳext / Ѳint UEQUIV
W/m
2
K
UPARALLEL
W/m
2
K
ΨBEAM
W/mK
Delta
% of U EQUIV
UNDERSLAB ASSEMBLY CLEAR FIELD – EU 1 YES
EN 6946
.205 .170 - BASELINE
UNDERSLAB ASSEMBLY AT BEAM – EU 2 YES
EN 6946
.711 .386 1.006 -247.0
UNDERSLAB ASSEMBLY AT COLUMN – EU 3 YES
EN 6946
.816 .169 1.294 -298.0

4b.1.4 Typical Window Jamb and Sill Analysis
Detail Location : W 1 AND W 2
All glazing assemblies use thermally broken aluminum frames and insulated glazing units (IGU) based on
the scheduled assembly indicated in chapter 3. Window jamb and window head are considered identical
in terms of thermal performance for this research.
A concurrent location of window frame and the insulation layer of the adjacent wall assembly can be
critical to efficient thermal performance. Any offset between the insulation layer and thermally-broken
window frame can reduce the effective thermal performance of the window assembly. The simulation
below with description – extended window frame location provides a comparative psi-value for windows
extended beyond the plane of the adjacent opaque wall assembly.
Analysis : Heat loss through length – psi-value per linear thermal bridge – simplified method.
Table 4b-6
ASSEMBLY - LOCATION SUBFRAME
Ѳext / Ѳint UPARALLEL
W/m
2
K
ΨJAMB
W/mK
A1 WINDOW JAMB – W 1 ACRIC
EN 6946
.193 .873
A1 WINDOW JAMB – W 1 GALV STL
EN 6946
.193 .814
A1 WINDOW JAMB – W 1 FIBERGLASS
EN 6946
.193 .852
EXTENDED WINDOW FRAME LOCATION
A1 WINDOW JAMB – W 1 ACRIC
EN 6946
.193 .818

A1 WINDOW SILL – W 2 ACRIC
EN 6946
.244 1.38
A1 WINDOW SILL – W 2 GALV STL
EN 6946
.191 .856
A1 WINDOW SILL – W 2 FIBERGLASS
EN 6946
.244 .814

A2 WINDOW JAMB – W 1 -
EN 6946
.233 .769
58

A2 WINDOW SILL – W 2 -
EN 6946
.216 1.465

A3 WINDOW JAMB – W 1 -
EN 6946
.220 .765
A3 WINDOW SILL – W 2 -
EN 6946
.220 1.193

4b.1.5 Base and Head of Wall at Ground Level Analysis
Detail Location : GF 1, GF 2, GF 3, HW 1, HW 2
Wall base transitions at slab-on-grade foundation can be difficult thermal bridges to mitigate. The edge
and thickness of a concrete slab is an effective conductor and retainer of thermal energy which can reduce
the effective U-value of the connecting wall or glazing assembly. Corresponding head of wall transitions
at exterior ceiling / soffit must effectively transition to the overall building envelope. Transitions from
glazing assemblies are more difficult to mitigate thermally due to required structural framing to support
the expanse of glass and glazing frame.
Analysis : Heat loss through length – psi-value per linear thermal bridge – simplified method

Table 4b-7
ASSEMBLY - LOCATION SUBFRAME
Ѳext / Ѳint UPARALLEL
W/m
2
K
ΨSILL
W/mK
A1 BASE OF WALL – GF 1 ACRIC
EN 6946
.255 1.81
A1 BASE OF WALL – GF 1 GLAV
EN 6946
.192 1.84
A1 BASE OF WALL – GF 1 FIBERGLASS
EN 6946
.255 1.81
INSULATED SLAB AND CURB EDGE W 1” RIGI INSUL
A1 BASE OF WALL W INSUL – GF 1 ACRIC
EN 6946
.255 1.07
HEAD OF WALL ASSEMBLIES
A1 HEAD OF WALL – HW 1 ACRIC
EN 6946
.271 .688
A1 HEAD OF WALL – HW 1 GLAV
EN 6946
.191 .698
A1 HEAD OF WALL – HW 1 FIBERGLASS
EN 6946
.218 .706

59

Analysis : Heat loss through length – psi-value per linear thermal bridge – simplified method.
Table 4b-8
ASSEMBLY-LOCATION GLAZING /
SUBFRAME
Ѳext / Ѳint UPARALLEL
W/m
2
K
ΨCURB /
FRAME
W/mK
A1 BASE OF WALL – GF 1 ACRIC
EN 6946
.255 1.81
BASE OF GLAZING ASSEMBLY – GF 2 1” IGU
EN 6946
1.613 1.573
BASE OF GLAZING ASSEMBLY – GF 3 13/16” LAM
EN 6946
5.181 1.406

A2 BASE OF WALL – GF 1 -
EN 6946
.214 1.160
A3 BASE OF WALL – GF 1 -
EN 6946
.220 1.159
HEAD OF WALL ASSEMBLIES
A1 HEAD OF WALL – HW 1 ACRIC
EN 6946
.271 .688
HEAD OF GLAZING ASSEMBLY – HW 2 1” IGU
EN 6946
.222 .410
HEAD OF GLAZING ASSEMBLY – HW 3 13/16” LAM
EN 6946
.222 .517

A2 HEAD OF WALL – GF 1 -
EN 6946
.220 .704
A3 HEAD OF WALL – GF 1 -
EN 6946
.220 .577

4b.1.6 Spandrel and Soffit Assembly Analysis
Detail Locations : IF 1, IF 2, IF 3
Spandrel conditions occur at perimeter of floor assembly intersects with the exterior wall. Typically, there
is a horizontal joint which allows for structural movement aligned where the structural frame connects to
the interior partition and ceiling assembly support.
Analysis : Heat loss through length – psi-value per linear thermal bridge – simplified method.
Table 4b-9

60

ASSEMBLY - LOCATION SUBFRAME
Ѳext / Ѳint UPARALLEL
W/m
2
K
ΨFLOOR
W/mK
A1 TYPICAL SPANDREL AT DRIFT JT – IF 1 ACRIC
EN 6946
.253 .924
A1 TYPICAL SPANDREL AT DRIFT JT – IF 1 GLAV
EN 6946
.192 .454
A1 TYPICAL SPANDREL AT DRIFT JT – IF 1 FIBERGLS
EN 6946
.253 .889

MITIGATED Z-CLIP HEAD-OF-WALL FRAMING AND SLAB EDGE W MINERAL WOOL INSUL

A1 TYPICAL SPANDREL AT DRIFT JT – IF 1 ACRIC
EN 6946
.253 .269

A2 TYPICAL SPANDREL AT DRIFT JT – IF 1 -
EN 6946
.219 .679
A3 TYPICAL SPANDREL AT DRIFT JT – IF 1 -
EN 6946
.219 .760

Soffit conditions occur at the interface between exterior ceiling elements and the exterior wall assembly.
Thermal transfer can occur on multiple sides of the construction and the location and extent of underslab
insulation is critical in reducing thermal transfer.
Analysis : Heat loss through length – psi-value per linear thermal bridge – simplified method.
Table 4b-10
ASSEMBLY - LOCATION SUBFRAME
Ѳext / Ѳint UPARALLEL
W/m
2
K
ΨFLOOR
W/mK
A1 TYPICAL SOFFIT – IF 2 ACRIC
EN 6946
.253 1.063
A1 TYPICAL SOFFIT – IF 2 GLAV
EN 6946
.191 0.989
A1 TYPICAL SOFFIT – IF 2 FIBERGLS
EN 6946
.253 1.025
A2 TYPICAL SOFFIT – IF 2 -
EN 6946
.218 .961
A3 TYPICAL SOFFIT – IF 2 -
EN 6946
.220 .963

A1 TYPICAL SOFFIT / WINDOW SILL – IF 3 ACRIC
EN 6946
.315 1.647
A1 TYPICAL SOFFIT / WINDOW SILL – IF 3 GLAV
EN 6946
.190 1.585
A1 TYPICAL SOFFIT / WINDOW SILL – IF 3 FIBERGLS
EN 6946
.320 1.639
A2 TYPICAL SOFFIT / WINDOW SILL – IF 3 -
EN 6946
.218 .519
A3 TYPICAL SOFFIT / WINDOW SILL – IF 3 -
EN 6946
.218 .600

61

4b.1.7 Roof Parapet Assemblies
Detail Locations R 1 and R 2
The roof parapet represents the primary junction between the roof assembly and exterior wall. This
interface is critical to ensure that the overall building envelope is thermally contiguous. The parapet wall
is a framed extension from the roof structural deck to a height specified by the building code. This
extension can be insulated or non-insulated within the framing cavity above the structural deck. The non-
insulated approach will result in a thermal bridge and reduction of the roof’s equivalent U-value. The
insulated approach will require the insulation of the parapet framing to a height of 15” above the roof
structural deck to mitigate the thermal bridge.
Ψ RF DK : Psi – value measured at structural roof deck interface with wall / parapet assembly.
Analysis : Heat loss through length – psi-value per linear thermal bridge – simplified method.
Table 4b-11
ASSEMBLY - LOCATION SUBFRAME
Ѳext / Ѳint UPARALLEL
W/m
2
K
ΨRF DK
W/mK
A1 TYPICAL PARAPET INSUL – R 1 ACRIC
EN 6946
.242 .969
A1 TYPICAL PARAPET NON INSUL- R 1 ACRIC
EN 6946
.242 .768
MITIGATED Z-CLIP HEAD-OF-WALL FRAMING AND SLAB EDGE W MINERAL WOOL INSUL
A1 TYPICAL PARAPET INSUL – R 1 ACRIC
EN 6946
.242 .266

A1 TYPICAL PARAPET INSUL- R 1 GLAV
EN 6946
.191 .634
A1 TYPICAL PARAPET INSUL- R 1 FIBERGLASS
EN 6946
.242 .862
A2 TYPICAL PARAPET INSUL- R 1 -
EN 6946
.223 .692
A3 TYPICAL PARAPET INSUL- R 1 -
EN 6946
.220 .727
GRAVEL STOP/ ROOF EDGE ASSEMBLY
A1 TYPICAL ROOF EDGE – R 2 ACRIC
EN 6946
.245 .496
A1 TYPICAL ROOF EDGE – R 2 GLAV
EN 6946
.192 .386
A1 TYPICAL ROOF EDGE – R 2 FIBERGLASS
EN 6946
.245 .480
A2 TYPICAL ROOF EDGE – R 2 -
EN 6946
.222 .544
A3 TYPICAL ROOF EDGE – R 2 -
EN 6946
.220 .619

62

4b.1.8 Corner Assemblies
Corner assembly analysis consists of inside and outside corner geometry with structural floor deck or
structural roof deck intersection. These details are complex involving geometric and linear thermal
bridges. Due to the complexity the detailed calculation method will be used to analyze the interface in 3
dimensions.
Detail Locations : C 1 and C 2
Analysis : 3D based geometric bridge – detailed calculation method.
Table 4b-12
ASSEMBLY - LOCATION SUBFRAME
Ѳext / Ѳint UPARALLEL
W/m
2
K
ΨCORNER
W/mK
A1 TYPICAL OUTSIDE CORNER – C 1 ACRIC
EN 6946
.193 .640
A1 TYPICAL OUTSIDE CORNER – C 1 GALV
EN 6946
.193 .457
A1 TYPICAL OUTSIDE CORNER – C 1 FIBERGLS
EN 6946
.193 .593
A2 TYPICAL OUTSIDE CORNER – C 1 -
EN 6946
.220 .729
A3 TYPICAL OUTSIDE CORNER – C 1 -
EN 6946
.221 .359

A1 TYPICAL INSIDE CORNER – C 2 ACRIC
EN 6946
.197 .519
A1 TYPICAL INSIDE CORNER – C 2 GALV
EN 6946
.197 .395
A1 TYPICAL INSIDE CORNER – C 2 FIBERGLS
EN 6946
.197 .480
A2 TYPICAL INSIDE CORNER – C 2 -
EN 6946
.220 .379
A3 TYPICAL INSIDE CORNER – C 2 -
EN 6946
.221 .352

4b.1.9 Canopy and Brow Roof Structural Projection Analysis
Exposed and enclosed structural support framing extended through the exterior wall assembly to construct
canopy and brow roof extensions. Simulated details are based on a 6” x 6” x ½” HSS tube frame
extension attached to the edge of the structural deck at 5’-0” o.c. The brow roof detail encloses the tube
frame with sheathing and the HDPE air barrier membrane.
Detail Locations : B 1, B 2 and B 3
Analysis : Heat loss through length – psi-value per linear thermal bridge – simplified method.
Table 4b-13
63

ASSEMBLY - LOCATION SUBFRAME
Ѳext / Ѳint UPARALLEL
W/m
2
K
ΨFLR
W/mK
A1 TYPICAL BROW PROJECTION – B 1 ACRIC
EN 6946
.265 2.341
A1 TYPICAL BROW PROJECTION – B 1 GALV
EN 6946
.192 2.045
A1 TYPICAL BROW PROJECTION – B 1 FIBERGLS
EN 6946
.265 2.264
A2 TYPICAL BROW PROJECTION – B 1 -
EN 6946
.224 2.145
A3 TYPICAL BROW PROJECTION – B 1 -
EN 6946
.220 2.115

A1 TYPICAL BROW AT WINDOW – B 2 ACRIC
EN 6946
.193 2.673
A1 TYPICAL BROW AT WINDOW – B 2 GALV
EN 6946
.192 2.288
A1 TYPICAL BROW AT WINDOW – B 2 FIBERGLS
EN 6946
.193 2.579
A2 TYPICAL BROW AT WINDOW – B 2 -
EN 6946
.220 2.340
A3 TYPICAL BROW AT WINDOW – B 2 -
EN 6946
.220 2.023

A1 TYPICAL CANOPY PROJECTION – B 1 ACRIC
EN 6946
.265 2.459
A1 TYPICAL CANOPY PROJECTION – B 1 GALV
EN 6946
.192 2.490
A1 TYPICAL CANOPY PROJECTION – B 1 FIBERGLS
EN 6946
.265 2.456
A2 TYPICAL CANOPY PROJECTION – B 1 -
EN 6946
.222 2.619
A3 TYPICAL CANOPY PROJECTION – B 1 -
EN 6946
.220 2.618

Fig 4b-2 Psi-Value per Junction

64

4b.2 Y-Value non-repeating linear thermal bridging calculations
The expression of linear heat loss transmission from thermal bridging is expressed through the envelopes Y-value.
The Y-value for each assembly detail is calculated based on the total length of each detailed condition and the total
area of the façade. Complete Y-value calculations per assembly type based on the preceding psi values are located in
Appendix E. Y-value heat loss per linear thermal bridging is in addition to the U-value transmission heat loss
prescribed to clear-field wall, roof and slab assemblies as indicated in the building code. Y-value heat loss should be
added to the standard U-value heat loss calculation for total heat loss through the envelope.
A EXP : Represents the total area of the building’s façade less the area of the parapet extension above the roof
assembly.
Total Envelope Area of Contextual Office Building Model :
ELEVATION TOTAL WALL AREA
SQ METERS SQ FEET
OPAQUE WALL AREA
SQ METERS SQ FEET
GLAZED WALL AREA
SQ METERS SQ FEET
NORTH 842 9060 493 5303 349 3757
SOUTH 812 8747 545 5696 283 3051
EAST 365 3926 230 2477 135 1449
WEST 366 3945 201 2164 165 1781
TOTAL AREA 2404 25878 1454 15650 933 10038

Fig 4b-3 Thermal Transmission Loss Diagram
Junction between assemblies with high insulation values C 1, C 2 , R 1, R 2
Junction between assemblies with disparate insulation values W 1, W 2
Junction between assemblies at movement joint IF 1, IF 2, IW 1, B 1
Junction between insulated and non-insulated assemblies GF 1, GF 2, GF 3,

65

Y-value Transmission at Non-Perimeter Structural Framing Through the Roof Assembly

Total area of the upper and lower roof assemblies less the brow projections is 2050 m
2
(22,064.5 ft
2
). The total linear
transmission through the roof assembly is related to the length and spacing of continuous structural framing which
bridges the roof diaphragm. This is calculated as the total length of beam, less the perimeter beams which are
accounted for in the parapet and roof edge calculations.

ASSEMBLY - LOCATION CEILING
Psi (Ψ)
W/mK
Length
Meters Feet
HTB
W/K
AEXP
m
2
Y-value
W/m
2
K
ROOF ASSEMBLY W BEAM / PTN – ER2 YES .004 542 1778.5 2.2 2050 .001
ROOF ASSEMBLY W BEAM / PTN – ER2 NO .071 542 1778.5 38.5 2050 .018

There is a 90% reduction in thermal transmission by non-perimeter structural framing through the roof assembly
when an interior ceiling assembly is present.

Fig 4b-4 Roof Diagram

66

Y-value Transmission at Non-Perimeter Structural Framing Through the Elevated Slab Assembly

Total area of the elevated slab assemblies less the brow projections is 845m
2
(9100 ft
2
). The total linear transmission
through the elevated assembly is related to the length and spacing of continuous structural framing which bridges the
insulated floor diaphragm. This is calculated as the total length of beam.

ASSEMBLY - LOCATION SPF
Psi (Ψ)
W/mK
Length
Meters Feet
HTB
W/K
AEXP
m
2
Y-value
W/m
2
K
ROOF ASSEMBLY W BEAM / PTN – EU 2 YES 1.006 319 1046 320 845 .38

Fig 4b-5 Elevated Slab Diagram

Total Envelope Area : 2404 m
2
+ 2050 m
2
+ 845 m
2
= 5299 m
2
(57,038 ft
2
)
Y-Value Transmission per Assembly Type :
A1.1 = .669 W/m
2
K
A1.2 = .578 W/m
2
K
A1.3 = .640 W/m
2
K
A2 = .587 W/m
2
K
A3 = .565 W/m
2
K
67

Total Y-Value Transmission per Assembly Type
Y- VALUE W/m
2
K

Fig 4b-6

Y-value Transmission Allocation Per Transition Location
ALLOCATION PER TOTAL Y-VALUE

Fig 4b-7

68

4b.3 Results
Analysis results indicate that window and spandrel details contribute 81% - 87% of linear thermal transmittance
through the building envelope based on the proposed contextual building design. Details classified as spandrel
conditions in the contextual energy model include IF 1,IF 2 and B 1. Spandrel details are distinguished as areas of the
wall assembly intersected by the adjacent floor assembly creating a linear thermal bridge along the perimeter length
of the floor slab. Details classified as window conditions in the contextual energy model include W 1, W 2, IF 3 and B 2.
Windows details are distinguished as areas of the wall assembly with framed openings for fixed or operable
windows. The window detail analysis in this research includes the intersection of the adjacent floor assembly into
the section of wall which forms the sill condition of the window. The total length of the all window conditions
within the contextual energy model equals 1125 meters (3691 ft) and the total length of spandrel conditions equals
744 meters (2441 ft). These are considerable lengths of thermal conduction through the building envelope and can
be assessed as the major contributors to the envelopes Y-value. It should be noted, that the overall length of linear
thermal bridges associated with the total number of windows is related to the 40% wall-to-window ratio established
as a basis for design.
The total Y-value for each wall assembly represents the sum of all transitional details related to the contextual
building design. The Y-value represents the amount of additional heat flow allocated at all linear thermal bridging
junctions and is an additive value to be summed with the U-value of the envelope to derive the total thermal
transmittance through the buildings envelope. Analysis indicates that the A1.1 and A1.3 rainscreen subframes
contribute the highest values toward linear thermal bridging. The A1.2 and A3 rainscreen subframe and assembly
contribute the lowest values toward linear thermal bridging. The heat loss contribution for each of these assemblies
shall be factored into the performance of the envelope through the contextual energy model.
The mitigation of spandrel, roof parapet, roof edge and corner details require an attention to the insulation of the
cavities formed from the edge-of-slab to the head of wall connection at the structural frame. This ‘spandrel’or ‘beam
pocket’ condition must be adequately insulated including the area around z-clips which extend from the structural
beam to the head-of-wall; adequate insulation of this area can reduce the psi value of the transition by 70% and
account for a ±3% reduction in annual source energy in the contextual model.

Fig 4b-8 Spandrel Areas of Thermal Discontinuity Fig 4b-9 Spandrel Heat Flow at Junction

69

CHAPTER 4c
4c. CONTEXTUAL WHOLE-BUILDING ENERGY ANALYSIS

4c.1 Introduction
Contextual whole-building energy simulations were conducted in seven cities corresponding to the seven ASHRAE
climate zones. The requirements of the contextual building model were based on the specifications enumerated in
chapter 3. Baseline simulations were conducted using calculated U-values for all assemblies with wall construction
specific to the A1, A2 and A3 assemblies. The effects of thermal transmission due to thermal bridging was not
accounted for in the baseline models. The total annual energy use of each simulation is based on nine categories
related to overall building operation, systems operation, and sensible heat gain through the envelope. The results
from the baseline simulations will be compared with corresponding simulations which include thermal bridging
values as discussed in pervious chapters.
Five thermally bridged simulations were conducted using the equivalent U-values for all assemblies with
construction specific to the A1, A2 and A3 assemblies describe in chapter 3. These equivalent U-value assemblies
include the effects of integral point thermal transmittance as defined in chapter 1. Psi values for all detailed
transitions were included to simulate the effects of linear thermal transmittance at the designated junctions. This
effectively integrates the Y-value thermal transmissions summarized in the previous chapter into the energy
simulation and final performance results.

BL Baseline model simulation results
Δ Delta percentage change between baseline and bridge model version.
Total Site Energy represents the amount of energy delivered to the building by a utility and is related to the end
use.
Total Source Energy represents the total energy used by a building including transmission and production loss and
delivery efficiency.
Energy Use Intensity (EUI) represents a buildings energy use in terms of its size and characteristics. The following
EUI calculations are based on Total Source Energy per EPA requirements.

70

4c.1.1 Contextual Model Simulation – Miami Florida

City/ State : Miami Florida Climate Zone : 1A
Economizer : No Climate File Location : Miami Intl Airport TMY3
HVAC : VAV w PFP Box Slab-on-Grade : Non - Insulated
Winter / Summer Design Temp : 50.5 °F ( 10.3°C) 78.7°F (25.9 °C)
Table 4c-1
SIMULATION
SUBFRAME ASSEMBLY
TOTAL SITE ENERGY
(kWh)
TOTAL SOURCE ENERGY
(kWh)
HEATING (kWh)
COOLING (kWh)
EXTERIOR LGHTING (kWh)
INTERIOR LGHTING (kWh)
INTERIOR EQUIP (kWh)
WATER SYSTEMS (kWh)
EUI (Kbtu/ft
2
)
OPAQUE INT SURFACE
SENSIBLE HEAT GAIN (GJ)
A1 TYPICAL VENTILATED RAINSCREEN WALL ASSEMBLY
BL RNSCN 830,054.0 1,772,157.0 22.8 412,005.0 3,942.0 31,537.0 352,864.0 29,683.0 113 1.2
A1.1 ACRIC 846,880.0 1,809,726.0 141.0 419,650.0 3,942.0 29,998.0 362,643.0 30,505.0 115 0.8
Δ
- +2% +2% +518% +2% 0% -5% +3% +3% +2% -33%
A1.2 GALV 846,983.0 1,809,825.0 137.0 419,757.0 3,942.0 29,998.0 362,643.0 30,505.0 115 0.9
Δ
- +2% +2% +501% +2% 0% -5% +3% +3% +2% -25%
A1.3 FBGLS 847,058.0 1,809,967.0 131.0 419,801.0 3,942.0 30,036.0 362,643.0 30,505.0 115 0.9
Δ
- +2% +2% +475% +2% 0% -5% +3% +3% +2% -25%
A2 TYPICAL DRAINAGE PLANE RAINSCREEN WALL ASSEMBLY
BL PLSTR 855,226.0 1,824,591.0 30.0 425,115.0 3,942.0 32,442.0 363,150.0 30,548.0 115 1.2
A2 PLSTR 848,433.0 1,812,850.0 140.0 420,510.0 3,942.0 30,048.0 363,239.0 30,555.0 115 0.9
Δ
- 0% 0% +367% -1% 0% -2% 0% 0% 0% -25%
A3 TYPICAL FACE BRICK VENEER VENTILATED RAINSCREEN ASSEMBLY
BL BRCK 843,406.0 1,800,426.0 26.0 418,746.0 3,942.0 32,031.0 358,504.0 30,157.0 114 1.2
A3 1A 838,231.0 1,791,896.0 132.0 415,058.0 3,942.0 29,713.0 359,173.0 30,213.0 114 0.9
Δ
- 0% 0% +408% 0% 0% -7% 0% 0% 0% -25%

Heat loss from linear thermal bridge junctions account for 0.8 % of total source energy for all assemblies.
71

4c.1.2 Contextual Model Simulation – Houston Texas

City/ State : Houston Texas Climate Zone : 2A
Economizer : No Climate File Location : Houston / Bush Intl Airport TMY3
HVAC : VAV w PFP Box Slab-on-Grade : Non - Insulated
Winter / Summer Design Temp : 35.1°F (1.7 °C) / 79.3 °F (26.3 °C)
Table 4c-2
SIMULATION
SUBFRAME ASSEMBLY
TOTAL SITE ENERGY
(kWh)
TOTAL SOURCE ENERGY
(kWh)
HEATING (kWh)
COOLING (kWh)
EXTERIOR LGHTING (kWh)
INTERIOR LGHTING (kWh)
INTERIOR EQUIP (kWh)
WATER SYSTEMS (kWh)
EUI (Kbtu/ft
2
)
OPAQUE INT SURFACE
SENSIBLE HEAT GAIN (GJ)
A1 TYPICAL VENTILATED RAINSCREEN WALL ASSEMBLY
BL RNSCN 722,540.0 1,667,309.0 1,758.0 300,762.0 3,932.0 33,542.0 352,864.0 29,683.0 106 3.3
A1.1 ACRIC 740,694.0 1,730,705.0 11,812.0 300,625.0 3,932.0 31,536.0 362,643.0 30,505.0 110 2.4
Δ
- +3% +4% +572% 0% 0% -6% +3% +3% +4% -27%
A1.2 GALV 740,326.0 1,728,776.0 11,210.0 300,500.0 3,932.0 31,536.0 362,643.0 30,505.0 110 2.4
Δ
- +2% +4% +538% 0% 0% -6% +3% +3% +4% -27%
A1.3 FBGLS 738,838.0 1,722,187.0 9,088.0 300,909.0 3,932.0 31,741.0 362,643.0 30,505.0 110 2.4
Δ
- +2% +3% +416% 0% 0% -6% +3% +3% +4% -27%
A2 TYPICAL DRAINAGE PLANE RAINSCREEN WALL ASSEMBLY
BL PLSTR 744,560.0 1,717,459.0 2,129.0 310,300.0 3,932.0 34,502.0 363,150.0 30,548.0 110 3.2
A2 PLSTR 741,775.0 1,732,483.0 11,477.0 300,984.0 3,932.0 31,588.0 363,239.0 30,555.0 110 2.4
Δ
- 0% +1% +439% -3% 0% -8% 0% +0% 0% -25%
A3 TYPICAL FACE BRICK VENEER VENTILATED RAINSCREEN ASSEMBLY
BL BRCK 734,281.0 1,694,366.0 1,929.0 305,694.0 3,932.0 34,065.0 358,504.0 30,157.0 108 3.3
A3 BRCK 732,315.0 1,710,791.0 10,888.0 296,873.0 3,932.0 31,237.0 359,173.0 30,213.0 108 2.4
Δ
- 0% +1% +464% -3% 0% -8% 0% +0% 0% -27%

Heat loss from linear thermal bridge junctions account for 0.8% of total source energy for all assemblies.
72

4c.1.3 Contextual Model Simulation – Los Angeles California

City/ State : Los Angeles California Climate Zone : 3B
Economizer : Yes Climate File Location : Los Angeles Intl Airport TMY3
HVAC : VAV w Reheat Slab-on-Grade : Non - Insulated
Winter / Summer Design Temp : 46.1°F (7.8 °C) / 67.9 °F (19.9 °C)
Table 4c-3
SIMULATION
SUBFRAME ASSEMBLY
TOTAL SITE ENERGY
(kWh)
TOTAL SOURCE ENERGY
(kWh)
HEATING (kWh)
COOLING (kWh)
EXTERIOR LGHTING (kWh)
INTERIOR LGHTING (kWh)
INTERIOR EQUIP (kWh)
WATER SYSTEMS (kWh)
EUI (Kbtu/ft
2
)
OPAQUE INT SURFACE
SENSIBLE HEAT GAIN (GJ)
A1 TYPICAL VENTILATED RAINSCREEN WALL ASSEMBLY
BL RNSCN 423,294.0 1,346,395.0 230.0 3,565.0 3,925.0 33,027.0 352,864.0 29,683.0 86 7.3
A1.1 ACRIC 433,792.0 1,380,592.0 1,452.0 3,548.0 3,925.0 31,718.0 362,643.0 30,505.0 88 7.6
Δ
- +2% +3% +531% 0% 0% -4% +3% +3% +2% +4.1%
A1.2 GALV 433,754.0 1,379,979.0 1,122.0 3,712.0 3,925.0 31,846.0 362,643.0 30,505.0 88 7.9
Δ
- +2% +2% +389% +4% 0% -4% +3% +3% +2% +8.2%
A1.3 FBGLS 433,760.0 1,379,938.0 1,171.0 3,750.0 3,925.0 31,765.0 362,643.0 30,505.0 88 7.9
Δ
- +2% +2% +409% +5% 0% -4% +3% +3% +2% +8.2%
A2 TYPICAL DRAINAGE PLANE RAINSCREEN WALL ASSEMBLY
BL PLSTR 435,562.0 1,385,403.0 277.0 3,685.0 3,925.0 33,977.0 363,150.0 30,548.0 88 7.2
A2 PLSTR 434,443.0 1,382,238.0 1,141.0 3,689.0 3,925.0 31,893.0 363,239.0 30,555.0 88 7.9
Δ
- -0.2% -0.2% +312% 0% 0% -6% 0% 0% 0% +9.7%
A3 TYPICAL FACE BRICK VENEER VENTILATED RAINSCREEN ASSEMBLY
BL BRCK 429,987.0 1,347,734.0 252.0 3,602.0 3,925.0 33,546.0 358,504.0 30,157.0 86 7.2
A3 1A 429,575.0 1,366,523.0 970.0 3,708.0 3,925.0 31,586.0 359,172.0 30,213.0 87 8.0
Δ
- 0% +1% +285% +3% 0% -6% 0% 0% +1% +11.1%

Heat loss from linear thermal bridge junctions account for 0.2% of total source energy for all assemblies.
73

4c.1.4 Contextual Model Simulation – Baltimore Maryland

City/ State : Baltimore Maryland Climate Zone : 4A
Economizer : Yes Climate File Location : Balt / Wash Intl Airport TMY3
HVAC : VAV w Reheat Slab-on-Grade : Insulated
Winter / Summer Design Temp : 16.7 °F (-8.5 °C) / 75.6 °F (24.2 °C)
Table 4c-4
SIMULATION
SUBFRAME ASSEMBLY
TOTAL SITE ENERGY
(kWh)
TOTAL SOURCE ENERGY
(kWh)
HEATING (kWh)
COOLING (kWh)
EXTERIOR LGHTING (kWh)
INTERIOR LGHTING (kWh)
INTERIOR EQUIP (kWh)
WATER SYSTEMS (kWh)
EUI (Kbtu/ft
2
)
OPAQUE INT SURFACE
SENSIBLE HEAT GAIN (GJ)
A1 TYPICAL VENTILATED RAINSCREEN WALL ASSEMBLY
BL RNSCN 579,666.0 1,642,862.0 49,000.0 108,016.0 3,924.0 36,179.0 352,864.0 29,683.0 105 29.4
A1.1 ACRIC 689,270.0 2,039,859.0 151,653.0 106,274.0 3,924.0 34,231.0 362,643.0 30,505.0 130 9.6
Δ
- +19% +24% +209% -2% 0% -5% +3% +3% +24 -67%
A1.2 GALV 675,383.0 1,988,741.0 137,077.0 106,607.0 3,924.0 34,427.0 362,643.0 30,505.0 127 9.9
Δ
- +17% +21% +180% -1% 0% -5% +3% +3% +21 -66%
A1.3 FBGLS 676,701.0 1,992,473.0 138,294.0 107,031.0 3,924.0 34,303.0 362,643.0 30,505.0 127 9.9
Δ
- +17% +21% +182% -1% 0% -5% +3% +3% +21 -66%
A2 TYPICAL DRAINAGE PLANE RAINSCREEN WALL ASSEMBLY
BL PLSTR 600,138.0 1,705,103.0 54,674.0 110,628.0 3,924.0 37,216.0 363,150.0 30,548.0 108 22.1
A2 PLSTR 667,787.0 1,997,132.0 138,983.0 106,611.0 3,924.0 34,476.0 363,239.0 30,555.0 127 9.8
Δ
- +11% +17% +154% -4% 0% -7% 0% 0% +18 -56%
A3 TYPICAL FACE BRICK VENEER VENTILATED RAINSCREEN ASSEMBLY
BL BRCK 590,562.0 1,676,234.0 51,950.0 109,283.0 3,924.0 36,744.0 358,504.0 30,157.0 107 25.7
A3 1A 663,841.0 1,950,893.0 130,613.0 105,751.0 3,924.0 34,168.0 359,173.0 30,213.0 124 10.0
Δ
- +12% +16% +151% -3% 0% -7% 0% 0% +16 -61%

Heat loss from linear thermal bridge junctions account for 14% of total source energy for assemblies A1.1, A1.2,
A1.3 and 15% of total source energy for assembly A2 and A3.
74

4c.1.5 Contextual Model Simulation – Chicago Illinois

City/ State : Chicago Illinois Climate Zone : 5A
Economizer : Yes Climate File Location : O’Hare Intl Airport TMY3
HVAC : VAV w Reheat Slab-on-Grade : Insulated
Winter / Summer Design Temp : 0.8 °F (-17.3 °C) / 74.3 °F (23.5 °C)
Table 4c-5
SIMULATION
SUBFRAME ASSEMBLY
TOTAL SITE ENERGY
(kWh)
TOTAL SOURCE ENERGY
(kWh)
HEATING (kWh)
COOLING (kWh)
EXTERIOR LGHTING (kWh)
INTERIOR LGHTING (kWh)
INTERIOR EQUIP (kWh)
WATER SYSTEMS (kWh)
EUI (Kbtu/ft
2
)
OPAQUE INT SURFACE
SENSIBLE HEAT GAIN (GJ)
A1 TYPICAL VENTILATED RAINSCREEN WALL ASSEMBLY
BL RNSCN 612,258.0 1,841,078.0 111,451.0 76,255.0 3,925.0 38,110.0 352,864.0 29,683.0 117 43.6
A1.1 ACRIC 776,829.0 2,440,522.0 270,788.0 73,022.0 3,925.0 35,946.0 362,643.0 30,505.0 155 11.9
Δ
- +27% +33% +143% -4% 0% -6% +3% +3% +32% -72.2
A1.2 GALV 757,938.0 2,370,852.0 251,165.0 73,535.0 3,925.0 36,164.0 362,643.0 30,505.0 150 12.8
Δ
- +24% +29% +126% -4% 0% -5% +3% +3% +28% -70.6
A1.3 FBGLS 759,178.0 2,374,907.0 252,352.0 73,626.0 3,925.0 36,027.0 362,643.0 30,505.0 151 12.7
Δ
- +24% +29% +126% -3% 0% -5% +3% +3% +29% -70.8
A2 TYPICAL DRAINAGE PLANE RAINSCREEN WALL ASSEMBLY
BL PLSTR 636,785.0 1,920,189.0 122,002.0 77,959.0 3,925.0 39,202.0 363,150.0 30,548.0 122 35.0
A2 PLSTR 761,253.0 2,382,706.0 253,848.0 73,471.0 3,925.0 36,214.0 363,239.0 30,555.0 152 12.6
Δ
- +20% +24% +108% -6% 0% -7% +.02% +.02 +25% -64.0
A3 TYPICAL FACE BRICK VENEER VENTILATED RAINSCREEN ASSEMBLY
BL BRCK 625,285.0 1,883,494.0 117,037.0 76,956.0 3,925.0 38,705.0 358,504.0 30,157.0 120 39.3
A3 1A 743,756.0 2,323,128.0 241,741.0 72,807.0 3,925.0 35,896.0 359,173.0 30,213.0 148 13.0
Δ
- +19% +23% +106% -5% 0% -7% +.2% +.2% +23% -66.9

Heat loss from linear thermal bridge junctions account for 19% of total source energy for assemblies A1.1, A1.2,
A1.3 and 17% of total source energy for assembly A2 and A3.
75

4c.1.6 Contextual Model Simulation – Minneapolis Minnesota

City/ State : Minneapolis Minnesota Climate Zone : 6A
Economizer : Yes Climate File Location : Min/St. Paul Intl Airport TMY3
HVAC : VAV w Reheat Slab-on-Grade : Insulated
Winter / Summer Design Temp : -9.4 °F / 72.7 °F (22.6 °C)
Table 4c-6
SIMULATION
SUBFRAME ASSEMBLY
TOTAL SITE ENERGY
(kWh)
TOTAL SOURCE ENERGY
(kWh)
HEATING (kWh)
COOLING (kWh)
EXTERIOR LGHTING (kWh)
INTERIOR LGHTING (kWh)
INTERIOR EQUIP (kWh)
WATER SYSTEMS (kWh)
EUI (Kbtu/ft
2
)
OPAQUE INT SURFACE
SENSIBLE HEAT GAIN (GJ)
A1 TYPICAL VENTILATED RAINSCREEN WALL ASSEMBLY
BL RNSCN 647,379.0 2,011,093.0 162,967.0 59,272.0 3,933.0 38,661.0 352,864.0 29,683.0 128 55.6
A1.1 ACRIC 843.424.0 2,722,514.0 352,844.0 56,700.0 3,933.0 36,799.0 362,643.0 30,505.0 176 13.7
Δ
- +30% +35% +117% -4% 0% -5% +2.8% +2.8% +37% -75.4
A1.2 GALV 822,644.0 2,646,366.0 331,473.0 57,109.0 3,933.0 37,002.0 362,643.0 30,505.0 168 14.8
Δ
- +27% +32% +104% -4% 0% -4% +2.8% +2.8% +31% -73.4
A1.3 FBGLS 824,162.0 2,651,515.0 332,973.0 57,233.0 3,933.0 36,875.0 362,643.0 30,505.0 169 14.7
Δ
- +27% +32% +104% -4% 0% -5% +2.8% +2.8% +32% -73.6
A2 TYPICAL DRAINAGE PLANE RAINSCREEN WALL ASSEMBLY
BL PLSTR 675,024.0 2,102,347.0 176,965.0 60,660.0 3,933.0 39,769.0 363,150.0 30,548.0 134 46.4
A2 PLSTR 826,457.0 2,659,758.0 334,557.0 57,117.0 3,933.0 37,057.0 363,259.0 30,555.0 169 14.6
Δ
- +22% +27% +89% -6% 0% -7% +.03 +.02 +26% -68.5
A3 TYPICAL FACE BRICK VENEER VENTILATED RAINSCREEN ASSEMBLY
BL BRCK 662,055.0 2,059,733.0 170,298.0 59,898.0 3,933.0 39,266.0 358,504.0 30,157.0 131 50.9
A3 BRCK 807,258.0 2,593,707.0 320,630.0 56,585.0 3,933.0 36,724.0 359,173.0 30,213.0 165 15.2
Δ
- +22% +26% +88% -6% 0% -6% +.2% +.2 +26% -70.0

Heat loss from linear thermal bridge junctions account for 14% of total source energy for assemblies A1.1, A1.2, A2
and A3 and 16% of total source energy for assembly A1.3.
76

4c.1.7 Contextual Model Simulation – Duluth Minnesota

City/ State : Duluth Minnesota Climate Zone : 7
Economizer : Yes Climate File Location : Duluth Intl Airport TMY3
HVAC : VAV w Reheat Slab-on-Grade : Insulated
Winter / Summer Design Temp : -15.1 °F / 67.6 °F (19.8 °C)
Table 4c-7
SIMULATION
SUBFRAME ASSEMBLY
TOTAL SITE ENERGY
(kWh)
TOTAL SOURCE ENERGY
(kWh)
HEATING (kWh)
COOLING (kWh)
EXTERIOR LGHTING (kWh)
INTERIOR LGHTING (kWh)
INTERIOR EQUIP (kWh)
WATER SYSTEMS (kWh)
EUI (Kbtu/ft
2
)
OPAQUE INT SURFACE
SENSIBLE HEAT GAIN (GJ)
A1 TYPICAL VENTILATED RAINSCREEN WALL ASSEMBLY
BL RNSCN 659226.0 2,173,740.0 220,478.0 12,224.0 3,919.0 40,098.0 352864.0 29,683.0 138 75.80
A1.1 ACRIC 886,041.0 2,992,054.0 439,979.0 11,381.0 3,919.0 37,613.0 362,643.0 30,505.0 190 17.1
Δ
- +34% +38% +99% -7% 0% -6% +3% +2.8% +38% -77%
A1.2 GALV 864,535.0 2,914,038.0 418,145.0 11,457.0 3,919.0 37,864.0 362,643.0 30,505.0 185 18.6
Δ
- +31% +34% +90% -6% 0% -5% +3% +2.8% +34% -75%
A1.3 FBGLS 866,006.0 2,919,358.0 419,749.0 11,484.0 3,919.0 37,706.0 362,643.0 30,505.0 186 18.5
Δ
- +31% +34% +90% -6% 0% -6% +3% +2.8% +35% -76%
A2 TYPICAL DRAINAGE PLANE RAINSCREEN WALL ASSEMBLY
BL PLSTR 689,573.0 2,277,382.0 238,190.0 12,523.0 3,919.0 41,243.0 363,150.0 30,548.0 145 64.9
A2 PLSTR 868,572.0 2,928,279.0 421,462.0 11,481.0 3,919.0 37,917.0 363,239.0 30,555.0 186 18.3
Δ
- +26% +29% +77% -8% 0% -8% +.02% +.1% +28% -76%
A3 TYPICAL FACE BRICK VENEER VENTILATED RAINSCREEN ASSEMBLY
BL BRCK 675,426.0 2,229,021.0 229,776.0 12,348.0 3,919.0 40,722.0 358,504.0 30,157.0 142 70.2
A3 1A 848,772.0 2,859,034.0 406,526.0 11,348.0 3,919.0 37,953.0 359,173.0 30,213.0 182 19.1
Δ
- +29% +28% +77% -8% 0% -7% +.2% +.2% +28% -73%

Heat loss from linear thermal bridge junctions account for 14% of total source energy for assemblies A1.1, A1.2, A2
and A3 and 16% of total source energy for assembly A1.3.
77

4c.1.8 Contextual Model Simulation – Fairbanks Alaska

City/ State : Fairbanks Alaska Climate Zone : 8
Economizer :Yes Climate File Location : Fairbanks Intl Airport TMY3
HVAC : VAV w Reheat Slab-on-Grade : Insulated
Winter / Summer Design Temp : -39.9 °F / 59.9 °F (15.5 °C)
Table 4c-8
SIMULATION
SUBFRAME ASSEMBLY
TOTAL SITE ENERGY
(kWh)
TOTAL SOURCE ENERGY
(kWh)
HEATING (kWh)
COOLING (kWh)
EXTERIOR LGHTING (kWh)
INTERIOR LGHTING (kWh)
INTERIOR EQUIP (kWh)
WATER SYSTEMS (kWh)
EUI (Kbtu/ft
2
)
OPAQUE INT SURFACE
SENSIBLE HEAT GAIN (GJ)
A1 TYPICAL VENTILATED RAINSCREEN WALL ASSEMBLY
BL RNSCN 833,145.0 2,822,477.0 389,892.0 1593.0 3898.0 55,214.0 352,864.0 29,682.0 180 104.3
A1.1 ACRIC 1,055,106.0 3,621,819.0 603,215.0 1209.0 3898.0 53,636.0 362,643.0 30,505.0 230 25.0
Δ
- + 27% +28% +55% -24% 0% -3% +3% +3% +28% -76%
A1.2 GALV 1,039,344.0 3,564,669.0 587,197.0 1247.0 3898.0 53,853.0 362,643.0 30,505.0 227 26.9
Δ
+ 25% +26% +51% -22% 0% -2% +3% +3% +26% -74%
A1.3 FBGLS 1,040,726.0 3,569,720.0 588,713.0 1248.0 3898.0 53,717.0 362,643.0 30,505.0 227 26.9
Δ
- + 25% +26% +51% -22% 0% -3% +3% +3% +26% -74%
A2 TYPICAL DRAINAGE PLANE RAINSCREEN WALL ASSEMBLY
BL PLSTR 871,356.0 2,955,196.0 415,328.0 1649.0 3898.0 56,802.0 363,149.0 30,548.0 188 91.41
A2 PLSTR 1,042,900.0 3,577,219.0 590,023.0 1245.0 3898.0 53,939.0 363,239.0 30,555.0 228 26.6
Δ
- + 20% +21% +42% -24% 0% -5% 0.02% 0.02% +21% -71%
A3 TYPICAL FACE BRICK VENEER VENTILATED RAINSCREEN ASSEMBLY
BL BRCK 853,660.0 2,893,682.0 403,418.0 1600.0 3898.0 56,083.0 358,504.0 30,157.0 184 97.59
A3 BRCK 1,024,010.0 3,511,020.0 576,059.0 1241.0 3898.0 53,426.0 359,173.0 30,213.0 223 27.7
Δ
- + 20% +21% +43% -22% 0% -5% +.2% +.2% +21% -72%

Heat loss from linear thermal bridge junctions account for 14% of total source energy for assemblies A1.1, A1.2, A2
and A3 and 16% of total source energy for assembly A1.3.
78

4c.1.9 Energy Use Intensity per Climate Zone and Assembly Type

ENERGY USE INTENSITY

Fig 4c-1 Energy Use Intensity per A1 PER assembly and Climate Zone

79

A2 DPR PLASTER ASSEMBLY A3 PER BRICK VENEER ASSEMBLY
ENERGY USE INTENSITY
Fig 4c-2 Energy Use Intensity per A2 & A3 assembly and Climate Zone
80

4c.1.10 Thermal Bridging Contribution to Annual Source Energy per Climate Zone

Fig 4c-3

4b.1 Results Summary

Whole-building analysis indicates that energy loss through the effects of thermal bridging is primary concentrated
on building heating system energy consumption and the major increase to building source energy is in climates that
are heating-dominant. The inclusion of transitional junction Psi values and their corresponding Y-value thermal
transmittance within the energy simulation process has a pronounced impact on the calculated R-value of all
envelope assemblies.
Climate Zones 1A and 2A : Hot-humid summers and temperate winters.
Both Miami Florida and Houston Texas are cooling dominant climates, although Houston has considerably colder
winters and a higher annual consumption related to the models heating systems. The higher heating system energy
use results in a slightly greater thermal conductance and annual energy use due to thermal bridging.
The A3 wall assembly is the most efficient envelope system for both climates based on simulation results. The A3
assembly has the lowest annual building energy use and is approximately 1% more efficient than the A1.3 assembly
which equates to an annual energy savings of 11-18,000 kWh of total source energy per year. In terms of the
panelized rainscreen assemblies, the A1.3 system is the most efficient system in Houston Texas, but the least
efficient in Miami Florida.
81

There is a ± 2% difference in annual energy use between the calculated baseline simulation and the A-series
assembly simulations which includes thermal bridging. The inclusion of thermal bridging values in the simulations
provided a different valuation of the tested assemblies than the baseline calculated simulations. Although, the
variance in annual energy use was not substantial, the efficiency of the designated assemblies changed when the psi-
values from the transitional details were added to the model.
Climate Zones 3A : Temperate, semi-arid climate with low humidity.
Los Angeles California is a cooling dominant climate, although the lack of humidity results in very low annual
cooling system consumption in comparison to zones 1A and 2A and equivalent annual heating system energy use.
The higher heating system energy use results in a slightly greater thermal conductance and annual energy use due to
thermal bridging.
The A3 wall assembly is the most efficient envelope system for this climate based on simulation results. The A3
assembly has the lowest annual building energy use and is approximately 1% more efficient than the A1.3 assembly
which equates to an annual energy savings of 13,000 kWh of total source energy per year. In terms of the panelized
rainscreen assemblies, the A1.3 system is the most efficient system in this climate zone.
There is a ± 2% difference in annual energy use between the calculated baseline simulation and the A-series
assembly simulations which includes thermal bridging. Although, the variance in annual energy use was not
substantial, the thermally bridged versions of the assemblies increase annual source energy consumption by
approximately 30-35,000 kWh per year.
Climate Zones 4A and 5A : Hot-humid summers and cold winters.
Both Baltimore Maryland and Chicago Illinois are heating dominant climates, although Chicago has considerably
colder winters and a higher annual consumption related to the models heating systems. The higher heating system
energy use results in a greater thermal conductance and annual energy use due to thermal bridging.
The A3 wall assembly is the most efficient envelope system for this climate based on simulation results. The A3
assembly has the lowest annual building energy use and is approximately 5% more efficient than the A1.2 assembly
which equates to an annual energy savings of 40-50,000 kWh of total source energy per year. In terms of the
panelized rainscreen assemblies, the A1.2 system is the most efficient system in this climate zone.
There is a ± 20-30% difference in annual energy use between the calculated baseline simulation and the A-series
assembly simulations which includes thermal bridging. The thermally bridged versions of the assemblies increase
annual source energy consumption by approximately 350-525,000 kWh per year.
Climate Zones 6A and 7 : Hot-humid summers and cold winters.
Both Minneapolis and Duluth Minnesota are heating dominant climates, although Duluth has considerably colder
winters and a ± 35% higher annual consumption related to the models heating systems. The higher heating system
energy use results in a greater thermal conductance and annual energy use due to thermal bridging.
The A3 wall assembly is the most efficient envelope system for this climate based on simulation results. The A3
assembly has the lowest annual building energy use and is approximately 6% more efficient than the A1.2 assembly
which equates to an annual energy savings of 50-50,000 kWh of total source energy per year. In terms of the
panelized rainscreen assemblies, the A1.2 system is the most efficient system in this climate zone.
There is a ± 25-38% difference in annual energy use between the calculated baseline simulation and the A-series
assembly simulations which includes thermal bridging. The thermally bridged versions of the assemblies increase
annual source energy consumption by approximately 650-750,000 kWh per year.
82

Climate Zones 8 : Subarctic climate with short temperate summers and extreme cold winters.
Fairbanks Alaska is a heating dominant climate with annual energy consumption primarily related to the models
heating systems. The higher heating system energy use results in a greater thermal conductance and annual energy
use due to thermal bridging.
The A3 wall assembly is the most efficient envelope system for this climate based on simulation results. The A3
assembly has the lowest annual building energy use and is approximately 5% more efficient than the A1.2 assembly
which equates to an annual energy savings of 54,000 kWh of total source energy per year. In terms of the panelized
rainscreen assemblies, the A1.2 system is the most efficient system in this climate zone.
There is a ± 21-28% difference in annual energy use between the calculated baseline simulation and the A-series
assembly simulations which includes thermal bridging. The thermally bridged versions of the assemblies increase
annual source energy consumption by approximately 775-800,000 kWh per year.

83

CHAPTER 5
5. SUMMARY OF FINDINGS AND DISCUSSION
5.1 Discussion Summary
Evaluation of the contextual energy model and corresponding thermal bridging calculations provides
insight into the effect thermal conductance has on annual building energy use. Simulation results are
comparable with the referenced research findings which identify thermal bridging can contribute 5%-20%
of total heat flow through the building envelope. (Theodoros, 2015) Analysis in all eight ASHRAE
climate zones provides a more comprehensive survey of thermal transmission through the building
envelope and its relationship with bio-climatic conditions. The inclusion of corrected U-values and linear
thermal bridging factors is shown to have a measurable impact on the accuracy of each energy model in
all climate zones; particularly with respect to the actual R-value of any envelope construction.

5.2 What is the contribution of thermal bridging to the reduction of building envelope
thermal resistance based on common North American rainscreen assembly
construction?
Analysis indicates that the contribution of point transmission thermal bridging through clear-field
assemblies is dependent on bio-climatic conditions. The magnitude of thermal transmission through
envelope bridges is most related to the difference between interior set-point temperature and winter
design low temperatures. This relationship is evident in the correlation between annual heating system
energy use and total building energy as measured with thermal bridging factors included in the envelopes
performance. Additionally, linear thermal bridging transmittance has a near-fixed contribution to annual
energy between 15%-19% in all climate zones. Thermal transmission through these construction details as
described in appendix B is difficult to mitigate due to the interface of steel and concrete with the exterior
wall / roof assemblies.
The addition of Y-value transmittance to the equivalent U-value transmittance of each wall assembly
changed the performative efficiency of wall and overall envelope in all climate zones simulated. The A1.3
rainscreen assembly with the fiberglass subframe had an R-value of 13 before the inclusion of linear
transmittance values. These values lowered the performative efficiency of the envelope by ±15%. This
resulted in the A1.2 rainscreen assembly with its galvanized furring subframe becoming the most efficient
PER assembly with a suspended façade panel in all heating dominant climates. The A3 PER assembly
with full brick veneer had an R-value of 11.6 before the inclusion of linear transmittance values. Given
that this assembly had the lowest Y-value contribution, energy simulation results indicate that this
assembly provides the most efficient envelope in all seven climate zones. Total annual source energy for
the A3 assembly was approximately 4-6% lower than any other assembly simulated.
Non-repeating linear thermal bridges
Linear transitional thermal bridges contribute 15-19% of annual energy use in heating-dominant climate
zones. This contribution is primarily dependent on floor slab-edge and supporting structural frame
intersections with the envelope. These conditions include spandrel, soffit, corner, parapet and roof edge
construction and account for over 80% of Y-value contributions to overall thermal transmittance. The
failure to adequately insulate gaps and support framing at these conditions has a decided effect on the
84

overall R-value of the wall assembly. Analysis results indicate that SPF or compressed mineral wool
insulation applied to this discontinuity will result in a 3-5% reduction in annual source energy use.
Thermal bridging contribution in cooling dominant climates
Thermal bridging contribution to annual energy use in cooling dominant climates could be considered
negligible in the context of standard building design and construction. However, within the framework of
NZEB building performance it should be noted that thermal bridging inclusion was critical in the
identification of the most efficient envelope assembly and ±2% increase in annual total energy use. This is
a small percentage, but it will still require a renewable energy equivalent which may justify the correct
simulation of thermal bridging values for NZEB projects within these climate zones. If a high R-value
wall assembly is selected to improve annual building performance, then non-repeating linear
discontinuities must be mitigated with insulation as described to insure overall envelope performance
maintains thermal resistance.
Table 5-1 Simulated Assemblies per Climate - Rated per Energy Use Performance
LOCATION ASSEMBLY RATING ANNUAL SOURCE ENERGY
DIFFERENCE BETWEEN BEST
AND WORST ASSEMBLY
CLIMATE ZONE CITY / STATE A1.1 A1.2 A1.3 A2 A3
1A Miami, Fla 2 3 4 5 1 21,000 kWh
2A Houston, Tx 4 3 2 5 1 21,700 kWh
3B Los Angeles, Ca 4 3 2 5 1 15,000 kWh
4A Baltimore, Md 5 2 3 4 1 89,000 kWh
5A Chicago, Ill 5 2 3 4 1 117,000 kWh
6A Minneapolis, Mn 5 2 3 4 1 129,000 kWh
7 Duluth, Mn 5 2 3 4 1 133,000 kWh
8 Fairbanks, AK 5 2 3 4 1 111,000 kWh

The difference in A1 assembly performance is 2-500 annual kWh in climates 1A, 2A and 3B per subframe.
The difference in the remaining climates is 50-70,000 annual kWh per subframe. The A3 assembly is the
best performer in all climate zones simulated.

5.3 How can thermal bridging be mitigated using select thermal break material
applications? Which material represents the best value in terms of adaptive applications
per designated detail locations?

Analysis indicates that SPF polyurethane insulation and pultruded fiberglass have the lowest conductivity
and highest adaptability to mitigate thermally bridged construction conditions. The SPF insulation can be
used to mitigate localized penetrations through the envelope where space constraints do not obstruct
installation. Aerogel coating is also applicable, although more expensive. Pultruded fiberglass is a low-
conductivity material which can be formed into various subframe attachment supports which inhibit the
85

thermal conductivity through the penetrating fastener in PER rainscreen applications. However, the
performance of the fiberglass subframe PER is heavily dependent on the number and type of linear
transition details in the proposed design. Analysis results indicate that the equivalent U-value of a
fiberglass subframe can be compromised by corresponding psi values related to specific construction
details and the extent of those details. This is an important finding related to the accuracy of R-value
calculations per envelope assembly construction. The inclusion of each details Psi value based on the
correct modeling and assignment of the constructions materials and geometry can have a pronounced
impact on the envelopes overall performance. These should be considered before specification of any
specific fabrication process or product. Linear thermal transmittance at transitional junction locations
must be mitigated to the same degree as the clear-field assemblies to ensure an accurate reading of
envelope performance.

5.4 Based on designated rainscreen assemblies, which application(s) have the best
performance per ASHRAE climate zone based on the contextual NZEB energy model?
Analysis indicates that the A3 full-brick veneer wall system is the least thermally conductive system and
produces the lowest annual building energy consumption in all eight ASHRAE climate zones. Total
annual site energy for the contextual model is approximately 20,000 kWh less with the A3 brick veneer
assembly when compared to all other tested assemblies. It should be noted that this system uses a
continuous insulation rigid board which is more resistive than the continuous mineral wool board
specified in the A1 wall assemblies. Additionally, the ventilation cavity and brick mass of the A3
assembly provides a thermal advantage when compared to the A2 cement plaster wall assembly. Psi
values related to the linear thermal transmittance of each detail transition were the lowest of all
assemblies simulated. The efficiency of this assembles linear conductance is most-likely related to the
type and spacing of the insulation fastener which also provide the tie-in with the brick courses. By
comparison, the A1 assemblies subframe is more conductive and has a greater number of fastener
penetrations. The A2 plaster assembly has a similar construction to the A3 but lacks the thermal mass of
the brick course and the 1” ventilation cavity. The drainage plane with its galvanized metal mesh layer is
more thermally conductive that the brick attachment system of the A3 assembly.
Clips vs Continuous Girts
The Psi-values and Y-values of subframe assemblies A1.1 (ACRIC) and A1.3 (Fiberglass) were highest
based on the number of fasteners required to attach non-continuous L-shaped brackets through the
envelope sheathing layer. These small clip configurations require (2) fasteners per location to prevent clip
rotation and provide a positive attachment. These clips had twice the number of fastener penetrations
through the envelope when compared with the continuous Z-girt and insulation fasteners used in the A1.2,
A2 and A3 assemblies. Although, the A1.3 (Fiberglass) clip was the least thermally conductive the
additional fastener penetrations increased its Y-value contribution and reduced its overall envelope
performance. By comparison, the A1.2 (Galv) continuous Z-girt required a single fastener spaced on
interval which reduced its Y-value contribution making it the most efficient subframe assembly in the A1
group. The A1.3 (Fiberglass) assembly would have performed better as a continuous girt or extruded
shape by reducing the number of required fasteners, although this would increase the cost considerably.
Ultimately, the best choice of assembly must be considered based on annual energy use savings in a
specific climate zone.
Assembly Implications on Annual Source Energy
86

The five thermally bridged rainscreen wall assemblies simulated contributed to the annual source energy
of the contextual model based on climate zone. In climate zones 1A, 2A and 3B the annual energy
difference between the best and worst preforming assembly accounted for 15-21,000 kWh per year. This
is not a significant amount of energy based on applicable renewable resources which would be available
for the contextual model. In climate zones 4A, 5A, 6A, 7 and 8 the annual energy difference between the
best and worst preforming assemblies accounted for 89-133,000 kWh per year. This amount of annual
energy does represent a substantial portion of any renewable offset; thus the selection of assembly is more
critical than in the other climates.
5.5 Implications for Current Energy Modeling and Evaluation Procedures
Professional energy analysis consultants working in the high-performance building sector follow similar
procedures to produce code compliant energy simulations. There are a variety of software applications for
whole-building energy analysis which must meet the compliance standards set by state and local
jurisdiction. Based on these restrictions, the inclusion of a thermal bridging allowance is typically
accounted for through a manipulation of an assemblies U-value (U-value correction) based on a
percentage increase in thermal transmission. There is no published standard or set of values which
determine this number, is it established by the consultant based on experience and custom; or is the result
of an equivalent U-value calculation based on the material layers of the assembly. The inclusion of a Y-
value or Psi value contribution is not common practice, hence there is always an underestimation of
annual energy use proportional to the amount and quality of non-repeating linear thermal bridges included
in a proposed design. Additionally, the assessment of roof assembly performance is usually completed
and calculated before the coordination and location of mechanical equipment, pads and utilities. This is
due to the placement of the energy modeling process in the sequence of the architectural design phases.
The omission of these and similar issues related to the accuracy of simulated envelope performance
values will result in an underestimation of energy loads and an inaccuracy in the expected efficiency of
the architectural design.

5.6 Implications for current regulatory requirements regarding mandatory envelope
performance factors and energy budgets.
Energy codes and standards in the United States set minimum efficiency requirements for new and
renovated buildings based on assumed energy use and emissions over the life of the building. Reference
standards such as ASHRAE 90.1 and the IECC set minimum performance requirements for construction
and building systems based on what is considered an acceptable efficiency prerequisite correlated to these
lifecycle factors. Thermal bridging, when accounted for, is typically a computer-generated recalculation
of the overall U-factor of the assembly. This process suffers from inaccuracy in the evaluation of the
construction of the assembly and inconsistent application depending on local code adoption and computer
simulation process.
Comparatively, the regulatory approach to thermal bridging in the European Union and Great Britain
differs from the United States in terms of methodology, convention, and compliance assessment. The
conventions and calculation requirements for linear thermal transmittance and specifically, the thermal
performance of construction junctions, does not exist in current model codes in the United States. This
deficiency produces an underestimation of thermal transmittance through the building envelope which
should be reevaluated based on established research and building performance objectives.
87

The inclusion of mandatory minimum Psi and Y-value contributions should be integrated into the
prescriptive and performance based approached to building energy compliance. This can be achieved
through adoption of methodology and related standards from Europe to North American climate zones
where thermal bridging contributions to annual energy use are considerable; primarily heating dominant
climates. Analysis of thermal bridging contribution can also be advantageous in accessing humidity and
condensation probabilities in climates with humid summers and in the selection of the most efficient
envelope assembly in NZEB projects.
5.7 Limitations and Future Work
Simulation engines and applications:
Current energy simulations software is limited in its ability to account for and evaluate the effects of
thermal bridging in terms of both clear-field equivalent U-values and linear transition Psi-values. The
ability to accurately account for these thermal conditions and parse the results based on overall energy
performance and the constituent performance of each condition makes accurate envelope and building
performance analysis difficult. Although, the software applications used in this research are validated for
simulation and analysis of thermal bridging they are restricted in their ability to output and correlate
results by their perspective simulation engines. Specifically, the ability of the EnergyPlus simulation
engine to output results related to thermal bridging factors is a detriment to the software’s application. A
parametric analysis application which can calculate an envelopes Y-value per assembly should be
developed with an interface which allows for the manipulation of Psi value inputs at designated junctions
in the building façade. The Y-value contribution should be reported within the context of the total
envelopes U and R value and annual energy use.
Contribution and analysis of a typical commercial building roof assembly:
A primary component in a buildings envelope enclosure is the roof assembly. The thermal conductivity of
the roof assembly is the primary defense against solar radiation, water infiltration, wind, ice, and snow.
However, the relationship between thermal bridging and roof construction has not been studied to the
same extent as wall construction. Within the context of a steel framed commercial building, the interface
between the steel structural frame, corrugated metal roof deck and concrete in-fill presents as a highly
conductive substrate with specific thermal discontinuities. The direct interface between structural steel
and insulated assembly makes any comparison with the typical wall assembly thermally incomparable.
The addition of numerous types of mechanical and service penetrations and platforms requires a deeper
analysis of roof assembly performance as relates to the building envelope.
Larger survey of Psi-values related to typical North American construction:
The construction details and wall assemblies identified and simulated as part of this research represent a
fraction of typical details common in the United States construction market. Future research should
expand the scope of analysis to include more details, assemblies and their contribution to heat loss via
thermal bridging.

88

CHAPTER 6
6. CONCLUSIONS
6.1 Conclusions

Design priorities for NZEB buildings focus on improved efficiency of all active and passive systems of
which the building envelope is a primary component. The nuances of thermal transmittance including all
the effects of thermal bridging are an important consideration in any envelope and whole-building energy
analysis. This research has indicated that inaccuracy or omission of thermal bridging factors related to
transitional junction details and clear-field assembly construction are consequential when evaluating
energy performance and NZEB objectives. The simulated contextual office building design and
construction details confirm that the contribution and effective mitigation of repeating and non-repeating
thermal bridges are an essential consideration in NZEB design and analysis.
The underestimation of annual energy loads due to the exclusion of thermal bridging has been thoroughly
documented in case study research. However, the relationship between climate, thermal conduction and
the proportional effects of thermal bridges has not been quantified or compared. Through comparison of
source and system energy in eight distinct climate zones with specific value inputs for non-repeating and
repeating thermal bridging conditions, this research provides a more accurate perspective into building
energy efficiency and its relationship to envelope performance.
Thermal conductance through envelope discontinuities are most pronounced when the temperature
difference between the interior and exterior environment is greater than 30°F. This results in buildings
located in heating dominant climates being the most susceptible to annual energy loss from thermal
bridging. Whole-building energy model simulations conducted in ASHRAE climate zone 4A-8 indicate
an increase in annual source energy of 16-28% and an almost identical increase in EUI. As winter design
temperatures decrease per climate zone the percentage of energy use related to the effects of thermal
bridging increases. In cooling dominant climates 1A-3B the increase in annual source energy increased 2-
4% and EUI increased from 0-2%.
The relationship between repeating thermal bridges calculated as equivalent U-values and non-repeating
linear thermal bridges calculated as Psi values is also dependent on climate zone and temperature
difference. The contribution of non-repeating linear thermal bridges to total envelope conductance
increases from cooling dominant to heating dominant environments. Climate zones 1A-3A indicate
contributions of 0.8-1.0%, where as climate zones 4A-8 indicate contributions of 15-19%. These
contributions were shown to be assembly specific and altered the expected performance of the wall
assemblies simulated; the R-values of specific assemblies were reduced based on the specific
contributions of conductance from the linear details when these were added to the energy model. The
accurate accounting of non-repeating linear bridges in current energy modeling procedure is a significant
deficiency to the production of accurate building energy use.
A series of mitigating strategies where simulated and analyzed to access their effectiveness in decreasing
thermal conductance through envelope bridging. In PER rainscreen assemblies with panelized subframe
cavity construction a standard galvanized Z-girt frame proved to be the most efficient and least expensive
assembly. Although a subframe comprised of pultruded fiberglass had better clear-field performance it
89

lost efficiency with the contribution of non-repeating linear bridges. The pultruded fiberglass was also
more costly than the Z-girt subframe ; the ACRIC aluminum subframe was the least efficient
construction. A variety of localized mitigation strategies where accessed to reduce subframe conductance
including low conductivity spacers, stainless steel fasteners and self-adhered flashing membranes. These
strategies showed a negligible impact on thermal transfer which is primarily influenced by the
conductance of the subframe clip, or girt material which magnifies heat flow through the fastener.
Analysis indicates that any substantial mitigation requires a decoupling of the subframe assembly from
the fastener which is penetrating the envelope.
Regardless of the mitigation strategies employed to reduce repeating thermal bridges a comparable
strategy must be used to mitigate non-repeating linear conductivity. Analysis indicates that over 80% of
linear conductance occurs where the slab edge and supporting structural frame intersect the exterior
envelope; this includes spandrel, window sill, parapet, and corner conditions. These areas may not be
adequately insulated due to congested support structures and lack of attention to gaps and discontinuities
in current construction trade craft. This oversight will generate higher Psi values, lower R-values for the
overall envelope, and an increase in annual energy use. The use of SPF or compacted mineral wool
insulation is recommended for these areas, especially in heating-dominant climates, or cooling dominant
climates where decreased overall wall U-factors are a necessity.
The effects of thermal bridging on envelope performance and building energy use are well established.
The adaptation of standards and procedures from Europe to the United States regulatory structure is
essential to promote accurate whole-building energy simulation results which account for all thermal
discontinues. This will promote an understanding of thermal bridging effects and countermeasures based
on established fundamentals and the nuances of North American climate and construction practices.

90

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93

Appendix A

Ref Junction Detail Ψ W/mK
Junctions
with an
external
wall
E1 Steel lintel with perforated steel base plate 0.05
E2 Other lintels (including other steel lintels) 0.05
E3 Sill 0.05
E4 Jamb 0.05
E5 Ground floor (normal) 0.16
E19 Ground floor (inverted) 0.07
E20 Exposed floor (normal) 0.32
E21 Exposed floor (inverted) 0.32
E22 Basement floor 0.07
E6 Intermediate floor within a dwelling 0.0
E7 Party floor between dwellings
a
0.07
E8 Balcony floor within a dwelling, wall insulation continuous
b
0.0
E9 Balcony between dwellings, wall insulation continuous
b,c
0.02
E23 Balcony within or between dwellings, balcony support penetrates wall
insulation
0.02
E10 Eaves (insulation at ceiling level) 0.06
E24 Eaves (insulation at ceiling level - inverted) 0.24
E11 Eaves (insulation at rafter level) 0.04
E12 Gable (insulation at ceiling level) 0.06
E13 Gable (insulation at rafter level) 0.08
E14 Flat roof 0.08
E15 Flat roof with parapet 0.56
E16 Corner (normal) 0.09
E17 Corner (inverted – internal area greater than external area) -0.09
E18 Party walls between dwellings
c
0.06
94

Ref Junction Detail Ψ W/mK
E25 Staggered party wall between dwellings
c
0.06
Junctions
with a
party wall
P1 Ground floor 0.08
P6 Ground floor (inverted) 0.07
P2 Intermediate floor within a dwelling 0.0
P3 Intermediate floor between dwellings 0.0
P7 Exposed floor (normal) 0.16
P8 Exposed floor (inverted) 0.24
P4 Roof (insulation at ceiling level) 0.12
P5 Roof (insulation at rafter level) 0.08
Junctions
within a
roof
R1 Head of roof window 0.08
R2 Sill of roof window 0.06
R3 Jamb of roof window 0.08
R4 Ridge (vaulted ceiling) 0.08
R5 Ridge (inverted) 0.04
R6 Flat ceiling 0.06
R7 Flat ceiling (inverted) 0.04
R8 Roof to wall (inverted) 0.06
R9 Roof to wall (flat ceiling) 0.04
(BRE, 2016)
a) Value of Ψ is applied to both sides of party floor
b) This is an externally supported balcony (the balcony slab is not continuous of the floor slab)
c) Value of Ψ is applied to both sides of each dwelling

95

Appendix B
Standard architectural details per designated location.

EW1 : A1 TYPICAL PLAN ACRIC EW1 : A1 TYPICAL PLAN GALV EW1 : A1 TYPICAL PLAN MCM
EW2 : A1 TYPICAL SECTION ACRIC EW2 : A1 TYPICAL SECTION GALV
ER1, ER2 : A1 TYPICAL ROOF SECTION ER3 , ER4 : A1 TYPICAL ROOF SECTION AT CONCRETE PAD
EW2 : A1 TYPICAL SECTION MCM
APPENDIX B
96
EU1 , EU2 : TYPICAL ELEVATED UNDERSLAB AT BEAM
EU3 : TYPICAL ELEVATED UNDERSLAB AT COLUMN
APPENDIX B
97
W1 : A1 TYPICAL PLAN ACRIC
W2 : A1 TYPICAL PLAN ACRIC
C1 : A1 TYPICAL OUTSIDE CORNER ACRIC C2 : A1 TYPICAL INSIDE CORNER ACRIC
W1 : A1 TYPICAL PLAN GALV
W2 : A1 TYPICAL PLAN GALV
APPENDIX B
98
GF1 : A1 TYPICAL WALL BASE ACRIC GF1 : A1 TYPICAL WALL BASE - INSULATED SLAB ACRIC
GF2 : A1 TYPICAL STOREFRONT BASE GF3 : A1 TYPICAL ALL-GLASS STOREFRONT BASE
APPENDIX B
99
HW1 : A1 TYPICAL WALL HEAD ACRIC
HW2 : A1 TYPICAL STOREFRONT HEAD
APPENDIX B
100
HW3 : A1 TYPICAL ALL-GLASS STOREFRONT HEAD
IF1 : A1 TYPICAL SPANDREL AT DRIFT JT ACRIC
APPENDIX B
101
IF2 : A1 TYPICAL SOFFIT ACRIC
IF3 : A1 TYPICAL SOFFIT AT WINDOW ACRIC
APPENDIX B
102
R1 : A1 TYPICAL ROOF PARAPET ACRIC
R2 : A1 TYPICAL ROOF EDGE ACRIC
APPENDIX B
103
B1 : A1 TYPICAL BROW ROOF ACRIC
APPENDIX B
104
B2 : A1 TYPICAL BROW ROOF AT WINDOW ACRIC
APPENDIX B
105
106

Appendix C
Standard architectural detail thermal bridging analysis per designated location.

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APPENDIX C
ROOF DRAIN PENETRATION W SPF INSULATION
ROOF DRAIN PENETRATION
ROOF ASSEMBLY AT STRUCTURAL FRAME
ROOF ASSEMBLY
4" SPF INSUL
107
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APPENDIX C
SMALL CONCRETE MECH PAD AT ROOF LARGE CONCRETE MECH PAD AT ROOF
SMALL CONCRETE MECH PAD AT ROOF W SPF INSUL LARGE CONCRETE MECH PAD AT ROOF W SPF INSUL
ELEVATED SLAB ASSEMBLY AT COLUMN
ELEVATED SLAB ASSEMBLY AT STRUCTURAL FRAME
4" SPF INSUL 4" SPF INSUL
4" SPF INSUL
4" SPF INSUL
108
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APPENDIX C
A1 OUTSIDE CORNER ASSEMBLY A2 OUTSIDE CORNER ASSEMBLY A3 OUTSIDE CORNER ASSEMBLY
A1 INSIDE CORNER ASSEMBLY A2 INSIDE CORNER ASSEMBLY A3 INSIDE CORNER ASSEMBLY
A1 WINDOW JAMB
A2 WINDOW JAMB
A3 WINDOW JAMB
109
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APPENDIX C
A1 SPANDREL AT INTERMEDIATE FLOOR LEVEL A2 SPANDREL AT INTERMEDIATE FLOOR LEVEL
A3 SPANDREL AT INTERMEDIATE FLOOR LEVEL
110
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APPENDIX C
A1 ROOF PARAPET A2 ROOF PARAPET
A3 ROOF PARAPET
A1 ROOF EDGE
12" INSUL
PARAPET WALL
NON INSUL
PARAPET WALL
12" INSUL
PARAPET WALL
12" INSUL
PARAPET WALL
111
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APPENDIX C
A1 SOFFIT A2 SOFFIT
A1 SOFFIT AT WINDOW SILL A2 SOFFIT AT WINDOW SILL
A3 SOFFIT
A3 SOFFIT AT WINDOW SILL
112

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APPENDIX C
A1 BROW ROOF PROJECTION
A1 BROW ROOF PROJECTION
AT WINDOW SILL
A1 HSS TUBE PROJECTION
113

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APPENDIX C
A2 BROW ROOF PROJECTION
AT WINDOW SILL
A2 BROW ROOF PROJECTION
A2 HSS TUBE PROJECTION
114

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APPENDIX C
A3 BROW ROOF PROJECTION
AT WINDOW SILL
A3 BROW ROOF PROJECTION
A3 HSS TUBE PROJECTION
115
116

Appendix D
Glossary of Terms, Acronyms, Abbreviations and Symbols

C-Value See Thermal Conductance C
Conductivity The quantity of heat transmitted per unit of time from a unit surface to an opposite unit surface
of on material per unit of thickness under a unit temperature differential.

Convection The transfer of heat from one point to another within a fluid by the mixing of one portion of the
fluid with another.

Diffusion The movement of individual molecules through narrow spaces by molecular velocity and
bouncing associated with individual gaseous or liquid molecules.

Dry-bulb
Temperature
The temperature of air as measured by a thermometer. DB
Efficiency The ratio of the useful work performed by a process to the total energy expended or heat taken
in.

Emissivity The ratio of radiant energy emited by a body to that emitted bby a perfect blackbody. A perfect
blackbody has a emissivity of 1, a perfect reflector an emissivity of 0.
H,I
Energy
Energy Use
Intensity
Total energy consumed by a building in one year divided by the area of the building. EUI
Infiltration Air leakage – intentional or unintentional introduction of outside air into the building.
R-Value See Thermal Resistance R
Thermal Bridge Part of the building envelope where the otherwise uniform thermal resistance is significantly
changed by full or partial penetration of the building envelope by materials with a different
thermal conductivity, and/or change in thickness of the fabric, and/or a difference between
internal and external areas, such as occur at wall / floor / ceiling junctions.

Thermal
Conductance
Time rate of steady-state heat flow through unit area of a material or construction.
Thermal
Coupling
Coefficient
Heat flow rate per temperature difference between two environments which are thermally
connected by the construction under consideration.

Thermal
Resistance
The reciprocal of the time rate of heat flow through a unit area induced by a unit temperature
difference between two defined surfaces of material or construction under steady-state
conditions.

Thermal
Transmittance
Heat transmission in unit time through unit area of a material or construction and the boundary
air films, induced by unit temperature difference between the environments of each side.

U-Value See Thermal Transmittance U

117

Appendix E
Y-value Linear Transmission Calculations

Y-value Transmission at all Detail Locations for Type A1, ACRIC Subframe Assemblies

ASSEMBLY - LOCATION SUBFRAME
Psi (Ψ)
W/mK
Length
Meters Feet
HTB
W/K
AEXP
m
2
Y-value
W/m
2
K
%
Y-value
A1 WINDOW JAMB – W 1 ACRIC .873 832 2730 726 5299 0.137 20.8
A1 WINDOW SILL – W 2 ACRIC 1.38 59 193 81 5299 0.015 2.1
A1 TYPICAL OUTSIDE CORNER – C 1 ACRIC .640 55 180 35 5299 0.007 .69
A1 TYPICAL INSIDE CORNER – C 2 ACRIC .519 19 61.5 10 5299 0.002 .28
A1 TYPICAL SPANDREL AT DRIFT JT – IF 1 ACRIC .924 126 414 116 5299 0.022 3.46
A1 TYPICAL SOFFIT – IF 2 ACRIC 1.063 25 81 27 5299 0.005 .69
A1 TYPICAL SOFFIT / WINDOW SILL – IF 3 ACRIC 1.647 13 43 21 5299 0.004 .8
A1 TYPICAL BROW PROJECTION – B 1 ACRIC 2.341 593 1947 1388 5299 0.262 40.1
A1 TYPICAL BROW AT WINDOW – B 2 ACRIC 2.673 221 725 591 5299 0.112 15.9
A1 TYPICAL PARAPET INSUL – R 1 ACRIC .969 201 660 195 5299 0.037 .55
A1 TYPICAL ROOF EDGE – R 2 ACRIC .496 43 140 21 5299 0.004 .6
A1 BASE OF WALL W INSUL – GF 1 ACRIC 1.81 104 340 188 5299 .003 .55
A1 HEAD OF WALL – HW 1 ACRIC .688 23 74.5 16 5299 .003 .48
STOREFRONT GLAZING ASSEMBLIES
BASE OF GLAZING ASSEMBLY – GF 2 1” IGU 1.573 6 20 9 5299 0.002 .28
HEAD OF GLAZING ASSEMBLY – HW 2 1” IGU .410 6 20 8 5299 0.002 .21
BASE OF GLAZING ASSEMBLY – GF 3 13/16” LAM 1.406 60 196 84 5299 0.016 2
HEAD OF GLAZING ASSEMBLY – HW 3 13/16” LAM .517 60 196 31 5299 0.006 .69
TOTAL HEAT LOSS TRANSMISSION .669

118

Y-value Transmission at all Detail Locations for Type A1, Galvanized Z-Girt Subframe Assemblies

ASSEMBLY - LOCATION SUBFRAME
Psi (Ψ)
W/mK
Length
Meters Feet
HTB
W/K
AEXP
m
2
Y-value
W/m
2
K
%
Y-value
A1 WINDOW JAMB – W 1 GALV .814 832 2730 677 5299 0.128 23
A1 WINDOW SILL – W 2 GALV .856 59 193 50.5 5299 0.010 1.7
A1 TYPICAL OUTSIDE CORNER – C 1 GALV .457 55 180 25 5299 0.005 .8
A1 TYPICAL INSIDE CORNER – C 2 GALV .395 19 61.5 7.5 5299 0.001 .2
A1 TYPICAL SPANDREL AT DRIFT JT – IF 1 GALV .454 126 414 57.2 5299 0.011 1.7
A1 TYPICAL SOFFIT – IF 2 GALV .989 25 81 24.7 5299 0.005 .8
A1 TYPICAL SOFFIT / WINDOW SILL – IF 3 GALV 1.585 13 43 20.6 5299 0.004 .7
A1 TYPICAL BROW PROJECTION – B 1 GALV 2.045 593 1947 1213 5299 0.229 41.3
A1 TYPICAL BROW AT WINDOW – B 2 GALV 2.288 221 725 505.6 5299 0.095 17.4
A1 TYPICAL PARAPET INSUL – R 1 GALV .634 201 660 127 5299 0.024 4.1
A1 TYPICAL ROOF EDGE – R 2 GALV .386 43 140 16.6 5299 0.003 .58
A1 BASE OF WALL W INSUL – GF 1 GALV 1.84 104 340 191 5299 0.036 6.6
A1 HEAD OF WALL – HW 1 GALV .698 23 74.5 16 5299 0.003 .58
STOREFRONT GLAZING ASSEMBLIES
BASE OF GLAZING ASSEMBLY – GF 2 1” IGU 1.573 6 20 9 5299 0.002 .3
HEAD OF GLAZING ASSEMBLY – HW 2 1” IGU .410 6 20 8 5299 0.002 .25
BASE OF GLAZING ASSEMBLY – GF 3 13/16” LAM 1.406 60 196 84 5299 0.016 2.5
HEAD OF GLAZING ASSEMBLY – HW 3 13/16” LAM .517 60 196 31 5299 0.006 .83
TOTAL HEAT LOSS TRANSMISSION .578

119

Y-value Transmission at all Detail Locations for Type A1, Fiberglass Subframe Assemblies

ASSEMBLY - LOCATION SUBFRAME
Psi (Ψ)
W/mK
Length
Meters Feet
HTB
W/K
AEXP
m
2
Y-value
W/m
2
K
%
Y-value
A1 WINDOW JAMB – W 1 FIBERGLS .852 832 2730 709 5299 0.132 20.7
A1 WINDOW SILL – W 2 FIBERGLS .814 59 193 48 5299 0.009 1.4
A1 TYPICAL OUTSIDE CORNER – C 1 FIBERGLS .593 55 180 33 5299 0.006 .7
A1 TYPICAL INSIDE CORNER – C 2 FIBERGLS .480 19 61.5 9 5299 0.002 .3
A1 TYPICAL SPANDREL AT DRIFT JT – IF 1 FIBERGLS .889 126 414 112 5299 0.021 3.6
A1 TYPICAL SOFFIT – IF 2 FIBERGLS 1.025 25 81 27 5299 0.005 .7
A1 TYPICAL SOFFIT / WINDOW SILL – IF 3 FIBERGLS 1.639 13 43 21 5299 0.004 .6
A1 TYPICAL BROW PROJECTION – B 1 FIBERGLS 2.264 593 1947 1343 5299 0.253 40
A1 TYPICAL BROW AT WINDOW – B 2 FIBERGLS 2.579 221 725 570 5299 0.108 17
A1 TYPICAL PARAPET INSUL – R 1 FIBERGLS .862 201 660 173 5299 0.033 4.9
A1 TYPICAL ROOF EDGE – R 2 FIBERGLS .480 43 140 21 5299 0.004 .6
A1 BASE OF WALL W INSUL – GF 1 FIBERGLS 1.81 104 340 188 5299 0.035 5.7
A1 HEAD OF WALL – HW 1 FIBERGLS .706 23 74.5 16 5299 0.003 .24
STOREFRONT GLAZING ASSEMBLIES
BASE OF GLAZING ASSEMBLY – GF 2 1” IGU 1.573 6 20 9 5299 0.002 .3
HEAD OF GLAZING ASSEMBLY – HW 2 1” IGU .410 6 20 8 5299 0.002 .2
BASE OF GLAZING ASSEMBLY – GF 3 13/16” LAM 1.406 60 196 84 5299 0.016 2.1
HEAD OF GLAZING ASSEMBLY – HW 3 13/16” LAM .517 60 196 31 5299 0.006 .7
TOTAL HEAT LOSS TRANSMISSION .640

120

Y-value Transmission at all Detail Locations for Type A2, DPR Assemblies

ASSEMBLY - LOCATION SUBFRAME
Psi (Ψ)
W/mK
Length
Meters Feet
HTB
W/K
AEXP
m
2
Y-value
W/m
2
K
%
Y-value
A2 WINDOW JAMB – W 1 - .769 832 2730 640 5299 0.121 20.6
A2 WINDOW SILL – W 2 - 1.465 59 193 86 5299 0.016 3
A2 TYPICAL OUTSIDE CORNER – C 1 - .729 55 180 40 5299 0.008 1.5
A2 TYPICAL INSIDE CORNER – C 2 - .379 19 61.5 7.2 5299 0.001 .2
A2 TYPICAL SPANDREL AT DRIFT JT – IF 1 - .679 126 414 85.6 5299 0.016 3
A2 TYPICAL SOFFIT – IF 2 - .961 25 81 24 5299 0.005 .7
A2 TYPICAL SOFFIT / WINDOW SILL – IF 3 - .519 13 43 6.7 5299 0.001 .2
A2 TYPICAL BROW PROJECTION – B 1 - 2.145 593 1947 1272 5299 0.240 40.5
A2 TYPICAL BROW AT WINDOW – B 2 - 2.340 221 725 517 5299 0.098 16.8
A2 TYPICAL PARAPET INSUL – R 1 - .692 201 660 139 5299 0.026 4.6
A2 TYPICAL ROOF EDGE – R 2 - .544 43 140 23 5299 0.004 .7
A2 BASE OF WALL W INSUL – GF 1 - 1.160 104 340 121 5299 0.023 3.8
A2 HEAD OF WALL – HW 1 - .740 23 74.5 17 5299 0.003 .5

BASE OF GLAZING ASSEMBLY – GF 2 1” IGU 1.573 6 20 9 5299 0.002 .3
HEAD OF GLAZING ASSEMBLY – HW 2 1” IGU .410 6 20 8 5299 0.002 .2
BASE OF GLAZING ASSEMBLY – GF 3 13/16” LAM 1.406 60 196 84 5299 0.016 2.3
HEAD OF GLAZING ASSEMBLY – HW 3 13/16” LAM .517 60 196 31 5299 0.006 .7
TOTAL HEAT LOSS TRANSMISSION .587

121
Y-value Transmission at all Detail Locations for Type A3, PER Assemblies

ASSEMBLY - LOCATION SUBFRAME
Psi (Ψ)
W/mK
Length
Meters Feet
HTB
W/K
AEXP
m
2
Y-value
W/m
2
K
%
Y-value
A3 WINDOW JAMB – W 1 - .765 832 2730 636 5299 0.120 19.9
A3 WINDOW SILL – W 2 - 1.193 59 193 70.4 5299 0.013 2.3
A3 TYPICAL OUTSIDE CORNER – C 1 - .359 55 180 19.7 5299 0.004 6
A3 TYPICAL INSIDE CORNER – C 2 - .352 19 61.5 6.7 5299 0.001 .2
A3 TYPICAL SPANDREL AT DRIFT JT – IF 1 - .760 126 414 95.7 5299 0.018 3
A3 TYPICAL SOFFIT – IF 2 - .963 25 81 24 5299 0.005 .8
A3 TYPICAL SOFFIT / WINDOW SILL – IF 3 - .600 13 43 7.8 5299 0.001 .2
A3 TYPICAL BROW PROJECTION – B 1 - 2.115 593 1947 1254 5299 0.237 39.8
A3 TYPICAL BROW AT WINDOW – B 2 - 2.023 221 725 447 5299 0.084 14.5
A3 TYPICAL PARAPET INSUL – R 1 - .727 201 660 146 5299 0.028 4.6
A3 TYPICAL ROOF EDGE – R 2 - .619 43 140 26.6 5299 0.005 .8
A3 BASE OF WALL W INSUL – GF 1 - 1.159 104 340 120.5 5299 0.023 3.8
A3 HEAD OF WALL – HW 1 - .220 23 74.5 5 5299 0.001 .2

BASE OF GLAZING ASSEMBLY – GF 2 1” IGU 1.573 6 20 9 5299 0.002 .3
HEAD OF GLAZING ASSEMBLY – HW 2 1” IGU .410 6 20 8 5299 0.002 .2
BASE OF GLAZING ASSEMBLY – GF 3 13/16” LAM 1.406 60 196 84 5299 0.016 2.3
HEAD OF GLAZING ASSEMBLY – HW 3 13/16” LAM .517 60 196 31 5299 0.006 .7
TOTAL HEAT LOSS TRANSMISSION .562

Abstract (if available)

Abstract In the United State, strategies to measure and mitigate Thermal Bridging are not as common place as those required in the European Union (EU) and detailed by the International Organization for Standardization (ISO). The distinction between regulatory requirements, construction methods, preferred materials, and bio-climatic conditions necessities an assessment of Thermal Bridging contribution to building energy performance within the context of the United States building, regulatory and construction environs. The additional impact of Thermal Bridging on heat transmission loss is not part of mandated energy calculations in which the U-value of the wall assembly is the only metric for façade performance. This research will examine typical thermal bridging locations and details based on popular ventilated rainscreen systems (face brick, thin brick, fibre cement panel, aluminum panel and phenolic panel) and access their contribution to envelope heat transmission loss. Thermal performance analysis will be based on current ISO, ASHRAE, NFRC and EU requirements. Then, the details (method of construction) and materials will be revised and/or augmented in an attempt to mitigate energy consumption and increase envelope performance. The final results will be assessed based on the performance criteria of a net-zero energy building (NZEB). ❧ As the number of verified and emerging Net-Zero Energy Buildings (NZEB) increases in the United States, strategies to reduce thermal loads imposed by bio-climatic conditions become an essential ingredient in reducing building Energy Use Intensity (EUI) toward a neutral balance between renewable and non-renewable energy sources. The contextual relationship between a buildings thermal envelope design and annual energy performance represents the primary research environment to measure the effects of Thermal Bridging junctions on overall building efficiency. The analysis of Thermal Bridges through the application of specified construction assemblies within the NZEB research prototype is an effective approach to facilitate research comparisons at the micro, meso and macro envelope scale. ❧ Although, products and strategies are available to mitigate the effects of Thermal Bridging these tend to be supplemental elements applied to established methods of façade construction. This research will analyze the supplemental approach as represented by a low-conductance material subframe attachment system in comparison with typical metal attachment systems and assemblies in 8 ASHRAE climate zones. Envelope performance comparisons will be based on annual source energy, EUI and cooling and heating system energy for each climate as defined by a representational city.

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Asset Metadata

Creator Grauer, Michael (author)

Core Title Mitigating thermal bridging in ventilated rainscreen envelope construction: Methods to reduce thermal transfer in net-zero envelope optimization

School School of Architecture

Degree Master of Building Science

Degree Program Building Science

Publication Date 07/25/2018

Defense Date 05/18/2018

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag building envelope,building performance,energy efficiency,energy use,facade,insulation,net-zero,OAI-PMH Harvest,rain screen,thermal bridging,thermal transmittance

Format application/pdf (imt)

Language English

Contributor Electronically uploaded by the author (provenance)

Advisor Konis, Kyle (committee chair), Choi, Joon-Ho (committee member), Noble, Douglas (committee member)

Creator Email mgr2820@gmail.com,mgrauer@usc.edu

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c89-27550

Unique identifier UC11671335

Identifier etd-GrauerMich-6452.pdf (filename),usctheses-c89-27550 (legacy record id)

Legacy Identifier etd-GrauerMich-6452.pdf

Dmrecord 27550

Document Type Thesis

Format application/pdf (imt)

Rights Grauer, Michael

Type texts

Source University of Southern California (contributing entity), University of Southern California Dissertations and Theses (collection)

Access Conditions The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the a...

Repository Name University of Southern California Digital Library

Repository Location USC Digital Library, University of Southern California, University Park Campus MC 2810, 3434 South Grand Avenue, 2nd Floor, Los Angeles, California 90089-2810, USA