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Embodied carbon of wood construction: early assessment for design evaluation

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EMBODIED CARBON OF WOOD CONSTRUCTION

Early Assessment for Design Evaluation

By

Rushita Vora

A Thesis Presented to the
FACULTY OF THE SCHOOL OF ARCHITECTURE
UNIVERSITY OF SOUTHERN CALIFORNIA
In partial fulfillment of the
Requirements of degree
MASTER OF BUILDING SCIENCE

MAY 2021

ii

TABLE OF CONTENTS
LIST OF TABLES ....................................................................................................................................... iv
LIST OF FIGURES ...................................................................................................................................... v
ABSTRACT ................................................................................................................................................ vii
1. INTRODUCTION ........................................................................................................................... 1
1.1 ENVIRONMENTAL IMPACT OF BUILDINGS ........................................................................................ 1
1.1.1 Life Cycle Assessment ............................................................................................................ 2
1.1.2 Embodied and Operational carbon .......................................................................................... 2
1.1.3 Incorporation of embodied carbon calculation in the design .................................................. 3
1.2 LOW-CARBON BUILDING MATERIALS ............................................................................................... 4
1.3 SUMMARY ........................................................................................................................................ 5
2. LITERATURE REVIEW ................................................................................................................ 7
2.1 WOOD AS A BUILDING MATERIAL .................................................................................................... 7
2.1.1 Environmental properties ........................................................................................................ 8
2.1.2 Structural properties ................................................................................................................ 9
2.1.3 Thermal properties ................................................................................................................ 10
2.1.4 Fire properties ....................................................................................................................... 12
2.1.5 Moisture content .................................................................................................................... 13
2.2 TIMBER CONSTRUCTION ................................................................................................................. 14
2.2.1 Engineered timber ................................................................................................................. 14
2.2.2 Timber structures .................................................................................................................. 17
2.2.3 Environmental impact ........................................................................................................... 21
2.3 EMBODIED CARBON ASSESSMENT .................................................................................................. 24
2.3.1 Limitations of current embodied carbon calculation methods in the early design stage ....... 26
2.3.2 Embodied carbon assessment of timber products ................................................................. 26
2.3.3 Building Information Modeling ............................................................................................ 29
2.3.4 Embodied Carbon in Construction Calculator ...................................................................... 32
2.4 SUMMARY ...................................................................................................................................... 33
3. METHODOLOGY ........................................................................................................................ 35
3.1 CASE STUDY 1: DEWITT-CHESTNUT APARTMENTS ....................................................................... 36
3.1.1 Composite-Timber Structure ................................................................................................. 38
3.1.2 All-Timber Structure ............................................................................................................. 40
3.2 CASE STUDY 2: KANCHANJUNGA APARTMENTS ........................................................................... 41
3.2.1 Cross Laminated Timber Structure ....................................................................................... 42
3.3 BUILDING INFORMATION MODELING ............................................................................................ 44
3.3.1 Material Quantity Verification .............................................................................................. 45
3.4 EMBODIED CARBON IN CONSTRUCTION CALCULATOR ................................................................. 46
3.4.1 Revit model to EC3 ............................................................................................................... 47
3.4.2 Material Information ............................................................................................................. 47
3.4.3 Allotment of EPDs ................................................................................................................ 48
3.4.4 Carbon Sequestration values ................................................................................................. 51
3.5 EMBODIED CARBON ANALYSIS ..................................................................................................... 51
3.5.1 EC3 tool ................................................................................................................................ 51
3.5.2 Microsoft Excel ..................................................................................................................... 52
3.6 COMPARATIVE ANALYSIS .............................................................................................................. 52
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3.6.1 Existing study embodied carbon calculations ....................................................................... 52
3.6.2 Analysis 1- Embodied carbon calculation methods .............................................................. 54
3.6.3 Analysis 2- Embodied carbon impact of a composite-timber and all-timber structure ......... 54
3.6.4 Analysis 3- Embodied carbon impact of a concrete and CLT structure ................................ 55
3.7 SUMMARY ...................................................................................................................................... 55
4. RESULTS AND DISCUSSION .................................................................................................... 57
4.1 MODELLING RESULTS .................................................................................................................... 57
4.1.1 Quantity Verification ............................................................................................................ 58
4.2 ANALYSIS 1 – EMBODIED CARBON CALCULATION METHODS ........................................................ 64
4.2.1 Embodied carbon calculations using EC3 tool...................................................................... 64
4.2.2 Embodied Carbon Calculation Verification .......................................................................... 67
4.2.3 Comparative analysis with study results ............................................................................... 68
4.2.4 Carbon Sequestration ............................................................................................................ 71
4.2.5 Summary of Analysis 1 ......................................................................................................... 73
4.3 ANALYSIS 2 – EMBODIED CARBON OF COMPOSITE-TIMBER AND ALL-TIMBER STRUCTURES ........ 74
4.3.1 Embodied carbon of composite-timber structure .................................................................. 74
4.3.2 Embodied carbon of all-timber structure............................................................................... 74
4.3.3 Comparative analysis between the structural systems .......................................................... 75
4.3.4 Carbon sequestration ............................................................................................................. 77
4.3.5 Summary of Analysis 2 ......................................................................................................... 79
4.4 ANALYSIS 3 – EMBODIED CARBON OF CONCRETE AND CLT STRUCTURES ................................... 80
4.4.1 Material quantities ................................................................................................................. 80
4.4.2 Transportation emissions ...................................................................................................... 81
4.4.3 Carbon sequestration ............................................................................................................. 83
4.4.4 Comparative analysis ............................................................................................................ 83
4.4.5 Summary of Analysis 3 ......................................................................................................... 86
4.5 SUMMARY ...................................................................................................................................... 87
5. CONCLUSIONS AND FUTURE WORK .................................................................................... 89
5.1 HYPOTHESIS 1 ............................................................................................................................... 89
5.2 HYPOTHESIS 2 ................................................................................................................................ 90
5.3 FUTURE WORK ................................................................................................................................ 92
5.3.1 Embodied Carbon Tools and Materials Databases ................................................................ 92
5.3.2 Carbon Sequestration ............................................................................................................ 92
5.3.3 Structural Connections .......................................................................................................... 93
5.3.4 Mass Timber .......................................................................................................................... 93
5.4 SUMMARY ...................................................................................................................................... 94
REFERENCES ........................................................................................................................................... 96

iv

LIST OF TABLES
Table 2-1 - Advantages and Disadvantages of wood .................................................................................. 14
Table 2-2 - Timber structural systems ........................................................................................................ 21
Table 2-3 - LCA tools ................................................................................................................................. 31
Table 3-1 - Benchmark building information ............................................................................................. 37
Table 3-2 - Structural properties ................................................................................................................. 38
Table 3-3 - Structural elements ................................................................................................................... 39
Table 3-4 - Summarized information about the Kanchanjunga Apartments .............................................. 41
Table 3-5 - Range of values from the EPDs allotted for Analysis 1 ........................................................... 49
Table 3-6 - Embodied carbon calculation for concrete ............................................................................... 50
Table 3-7 - Embodied carbon values for steel and rebar ............................................................................ 51
Table 4-1 - Structure material quantity verification of the composite-timber model ................................. 60
Table 4-2 - Foundation material quantities verification of the composite-timber model ........................... 61
Table 4-3 - Reinforcement and structural steel quantity calculation for the composite-timber model ...... 61
Table 4-4 - Structure material quantities verification of the all-timber model ........................................... 63
Table 4-5 - Reinforcement and structural steel quantity calculation for the all-timber model ................... 64
Table 4-6 - Embodied carbon values on Excel and EC3 tool ..................................................................... 68
Table 4-7 - Carbon sequestration values ..................................................................................................... 72
Table 4-8 - Embodied carbon impact change between the composite-timber and all-timber structure ...... 80
Table 4-9 - Structural material quantities ................................................................................................... 81
Table 4-10 - Transportation emissions ........................................................................................................ 82
Table 4-11 - Embodied carbon impact change between the concrete and CLT structure ........................... 87

v

LIST OF FIGURES
Figure 1-1 : Carbon storage and emissions for different building materials ................................................. 5
Figure 2-1 - Constituents of wood ................................................................................................................ 8
Figure 2-2 - Embodied energy and Young’s modulus of wood as compared to concrete and steel ............. 9
Figure 2-3 - Strength and density of wood as compared to steel and concrete ........................................... 10
Figure 2-4 - Thermal conductivity and yield strength of materials............................................................. 11
Figure 2-5 - Thermal conductivity and thermal expansion ......................................................................... 12
Figure 2-6 - Combustion of exposed wood ................................................................................................. 13
Figure 2-7 - Structural engineered timber products .................................................................................... 16
Figure 2-8 - Engineered timber manufacturing processes .......................................................................... 17
Figure 2-9 - Different structural systems .................................................................................................... 20
Figure 2-10 - Embodied carbon emissions for different timber products ................................................... 24
Figure 2-11 - Life cycle assessment stages ................................................................................................. 25
Figure 2-12 - Energy consumption for the manufacturing of timber products ........................................... 28
Figure 2-13 - System boundaries for CLT production ................................................................................ 29
Figure 2-14 - Sankey diagram used in EC3 ................................................................................................ 33
Figure 3-1 - Methodology Diagram ............................................................................................................ 36
Figure 3-2 - Dewitt-Chestnut Building ....................................................................................................... 37
Figure 3-3 - Overall structure of the composite-timber structure ............................................................... 40
Figure 3-4 - All-timber structure ................................................................................................................. 41
Figure 3-5 - Kanchanjunga Apartments ...................................................................................................... 42
Figure 3-6 - Structural design of the proposed CLT structure .................................................................... 43
Figure 3-7 - Existing concrete structure (left) and CLT structure (right) of Kanchanjunga Apartments ... 44
Figure 3-8 - Published estimated material quantities for composite-timber structure ................................ 46
Figure 3-9 - Published estimated material quantities for all-timber structure ............................................. 46
Figure 3-10 - EC3 Workflow ...................................................................................................................... 47
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Figure 3-11 - EPDs in EC3 categorized by material ................................................................................... 48
Figure 3-12 - Embodied carbon comparison between benchmark and composite-timber structure ........... 53
Figure 3-13 - Embodied carbon comparison between benchmark and composite-timber structure using
sustainable options ...................................................................................................................................... 54
Figure 4-1 - Report model (left) and Revit model (right) ........................................................................... 57
Figure 4-2 - Sankey diagram for composite-timber structure with mid-range EPDs ................................ 65
Figure 4-3 - Impact of material quantity change on embodied carbon calculations ................................... 66
Figure 4-4 - Comparative overall impact .................................................................................................... 67
Figure 4-5 - Comparative analysis with low-impact EPDs ......................................................................... 69
Figure 4-6 - Comparative analysis with mid-impact EPDs ........................................................................ 70
Figure 4-7 - Comparative analysis with high-impact EPDs ........................................................................ 70
Figure 4-8 - Comparative analysis without carbon sequestration ............................................................... 73
Figure 4-9 - Embodied carbon impact of the all-timber structure............................................................... 75
Figure 4-10 - Comparative analysis between the embodied carbon impact of the structures ..................... 76
Figure 4-11 - Structural layout of composite-timber (left) and all-timber (right) structures ...................... 76
Figure 4-12 - Comparative analysis with carbon sequestration .................................................................. 78
Figure 4-13 - Material impact comparison ................................................................................................. 79
Figure 4-14 - Comparative analysis between the concrete and proposed CLT structure ............................ 84
Figure 4-15 - Comparative analysis with transportation emissions ............................................................ 85
Figure 4-16 - Comparative analysis with carbon sequestration .................................................................. 86

vii

ABSTRACT
The impacts from the built environment are significant and therefore it is important to reduce the carbon
footprint of buildings. Technological advancements have made it possible to reduce the operational carbon
of the building, making it important to address the embodied carbon footprint of the building. The use of
low-carbon footprint and carbon sequestering materials can reduce the embodied carbon of a building,
which has led to a rise in the use of low carbon materials, such as timber, in the construction industry. The
low net embodied carbon of the material along with its structural properties makes it a very good material
for construction. The assessment of embodied carbon is a time consuming and complex task. This has
resulted in the absence of a particular method of calculation. A cradle-to-gate assessment of the embodied
carbon of a tall timber tower, using the Embodied Carbon in Construction Calculator (EC3) tool, was used
as a case study to understand the impact of the use of product specific Environmental Product Declarations
on embodied carbon calculations. The embodied carbon of different timber structural systems was
compared. In addition, the impact of transportation emissions on the net embodied carbon of buildings was
also studied by using a location specific case study.

The analyses showed that the EC3 tool enhanced the accuracy of the embodied carbon calculations by
providing precise manufacturer values, instead of industry values. The results also indicated that the method
produced a conservative analysis as it does not account for carbon sequestration by wood. The study also
showed that timber as a material for construction reduced the net embodied carbon of the building, even if
the carbon sequestered by wood is not accounted for and even if the timber product is not locally produced.
Sustainable forestry practices ensure the inclusion of the carbon sequestered by wood, which substantially
reduces the net embodied carbon, often resulting in a net negative embodied carbon. The analyses showed
the impact of carbon sequestration on the net embodied carbon footprint of the building, making it important
to sustainably manage forests. The forest source of the wood, the location of the manufacturing unit and
the location of the construction site are also important considerations for accurate embodied carbon
calculations.
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KEY WORDS
Timber, Engineered Timber, Embodied Carbon, Carbon Sequestration, Environmental Product
Declarations, Building Information Modelling

HYPOTHESIS
1. The use of product specific Environmental Product Declarations in the product stage results in a more
accurate calculation of the embodied carbon in comparison to a conventional life cycle analysis.
2. The use of an all-timber structural system results in a lower embodied carbon in comparison to a timber-
concrete structural system.

RESEARCH OBJECTIVES
1. To conduct an analysis of the embodied carbon for a tall timber and a hybrid timber building case
study using product specific Environmental Product Declarations.
2. To compare the results of the analyses with the existing life cycle analysis calculations for the same case
study building.
3. To explore the influence of transportation and carbon sequestration on the net embodied carbon footprint
of the building.
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1. INTRODUCTION
The world’s population is anticipated to grow from 7.7 billion to 10.9 billion by 2100 (Gladstone 2020). A
rise in population directly impacts the construction industry. New and rebuilt buildings are anticipated to
grow by two trillion square feet in the next 35 years (Architecture 2030 n.d.). Furthermore, 60% of the
world’s population is anticipated to migrate to urban areas by 2050 (Ali and Al-Kodmany 2012). Since land
is limited in urban areas, tall buildings will probably be needed to accommodate the growing population of
the cities. Tall buildings promote sustainability as they reduce suburban sprawl, have higher volume to skin
ratios, have shared floors and lower weather exposed surfaces, and make use of energy efficient central
systems (Skidmore, Owings & Merrill 2013). However, the quantity of structural materials required to
support tall buildings is higher. This impacts the environment negatively by increasing the building’s carbon
footprint. Since the construction of tall buildings is not avoidable, it becomes essential to build structures
that have a low negative impact on the environment.

1.1 Environmental impact of buildings
The built environment has a significant impact on the natural environment. It accounts for 38% of the total
carbon dioxide emissions and consumes 72% of the total electricity in the United States (U.S. Green
Building Council 2014). It is responsible for generating nearly 40% of the annual greenhouse gas emissions
globally ( Architecture 2030 n.d). There are several factors that lead to the high carbon footprint of buildings.
The energy used to operate and maintain buildings along with the energy spend in extracting, manufacturing,
and installing the materials result in high carbon emissions (United Nations Environmental Programme,
2009 as cited in Fenner et al. 2018). The overall impact of a building on the environment can be evaluated
using a method called life cycle assessment (LCA) (Khasreen, Banfill, and Menzies 2009).

2

1.1.1 Life Cycle Assessment
Life Cycle Assessment (LCA) is a method used to analyze the overall impact of a building on the
environment by evaluating the impact of all the materials and process used in the building (Khasreen,
Banfill, and Menzies 2009). It assesses the impact of a product throughout its life- extraction of raw
materials, all the processes involved in its production and manufacturing, transportation to the factory and
the site, installation on site and its disposal (Khasreen, Banfill, and Menzies 2009). This process is referred
to as cradle-to-grave. This is important to evaluate as a building uses energy in all stages of its life, starting
from resource extraction to its demolition (Khasreen, Banfill, and Menzies 2009).

1.1.2 Embodied and Operational carbon
A building uses energy directly for its construction, operation, maintenance and demolition, and indirectly
for the extraction, production, transportation and installation of the materials used (Khasreen, Banfill, and
Menzies 2009). Operational energy refers to the energy used by a building after it is constructed and
occupied for heating, cooling, lighting and the functioning of equipment (Iddon and Firth 2013). The
embodied energy of a building refers to the energy used indirectly for the extraction, production,
manufacturing, transportation, installation, replacement and disposal of construction materials. (Miller and
Ip 2013). The carbon emissions associated with the operational and embodied energy are referred to as
operational carbon and embodied carbon (Lockie and Berebecki 2012). The whole building lifecycle carbon
comprises of the operational and embodied carbon. Building features, like inefficient building envelopes
and insufficient ventilation, that result in an increase in the heating, cooling and lighting load directly lead
to an increase in the operational carbon. Systems that are required to heat, cool and ventilate a building
account for nearly half of the building’s total energy use (Khasreen, Banfill, and Menzies 2009). Employing
strategies like insulated building envelopes, multiple-glazed windows, shading devices to reduce the
building energy demand and using energy efficient HVAC systems can reduce the operational carbon of
the building (Shoubi et al. 2015) . The percentage contribution of the embodied carbon to the whole building
carbon is dependent on the location, the efficiency of the operational energy equipment and the climate
3

(Azari and Abbasabadi 2018). The use of carbon-intensive materials, less-durable materials, materials that
cannot be reused or recycled increase the embodied carbon of a building.

1.1.3 Incorporation of embodied carbon calculation in the design
Over 11% of the total greenhouse gas emissions and 28% of the total building sector emissions are caused
by the embodied carbon of annually (Architecture 2030 n.d.). A building’s heating, ventilation, and air
conditioning (HVAC) systems account for nearly 40% of the total building energy use (Khasreen, Banfill,
and Menzies 2009). With advances in technology, reducing the operational carbon of the building becomes
an achievable task, which makes the embodied carbon a larger contributor to the whole building life cycle
carbon (Azari and Abbasabadi 2018). Embodied carbon can account for 26-57% of the whole building
carbon in passive buildings and 74-100% in net zero buildings (Chastas et al. 2016 as cited in Azari &
Abbasabadi 2018). The embodied carbon of a building cannot be reduced once it is built, unlike the
operational carbon that can be reduced by selecting energy efficient systems and using renewable energy.
It is, therefore, essential to consider the embodied carbon footprint of the building in the design stages.
Embodied carbon is measured in kilograms of CO 2
e per kilogram of the material (Lockie and Berebecki
2012). CO
2
e or Carbon dioxide equivalent is the equivalent amount of CO
2
emissions which would have
the same global warming potential as the quantity of other greenhouse gases (DesignBuilder n.d.).
Embodied carbon for a building can be measured for different stages. A cradle-to-gate process includes the
carbon emissions from the mining, extraction, processing, manufacturing of raw materials and transporting
them to the factory; a cradle-to-site process includes the emissions from the cradle-to-gate stages and the
transportation of the products to the site; a cradle-to-end of construction process includes emissions from
the cradle-to-site process and construction and installation on site; a cradle-to-grave includes emissions
from the cradle-to-end of construction process, maintenance, repairs and disposal of the construction
materials; a cradle-to-cradle includes emissions from the cradle-to-grave process and the end-of-life use of
the material (Lockie and Berebecki 2012).

4

There are several ways of mitigating the embodied carbon footprint of a building. Using low-carbon
building materials, using local material to reduce the transportation-related emissions, reducing the
dependency of the structure on carbon-intensive materials, re-using and recycling materials, considering
end-of-life use of the materials, using more durable materials and using more efficient construction and
installation techniques to reduce installation-related emissions are some of the strategies that could reduce
the embodied carbon footprint of the building (Pomponi and Moncaster 2016).

1.2 Low-carbon building materials
The consideration of low-carbon materials is important as a square meter of habitable space uses 2.3 ton of
materials (Mahamadu, Baffour Awuah, and Booth 2016). With time, the use of materials has shifted from
zero energy materials, like bamboo, soil and wood, to more energy-intensive modern-day materials, like
concrete and steel. These materials utilize a lot of energy for their manufacturing process and production,
resulting in high carbon emissions and an increase in the embodied carbon (Cabeza et al. 2013; Pomponi
et al. 2020). In addition to this, these materials are usually transported to different parts of the world for use,
adding to the carbon footprint of the material and subsequently the building.

The embodied carbon of a material in the cradle-to-gate stages comprises of two categories of carbon
emissions. Raw materials CO 2
refers to the carbon emissions that are a result of raw material compounds
that convert into CO
2
during the manufacturing process and fuel-driven CO
2
refers to the carbon emissions
caused by the combustion of fossil fuels to manufacture the materials (Cabeza et al. 2013). The embodied
carbon of a material can be reduced by using materials whose raw material compounds do not generate CO
2

emissions for their manufacturing and by using materials whose manufacturing process is not carbon
intensive. The use of natural materials like wood, bamboo, strawbale, adobe, etc. can reduce the embodied
carbon of the materials by eliminating the emissions that result from the manufacturing processes of raw
materials (Figure 1-1). Natural and organic materials act as a carbon sink by converting CO
2
to biomass
during the growth of the plant, using photosynthesis (Pomponi et al. 2020). However, not all naturally
5

occurring materials provide structural strength comparable to materials like steel and concrete. Wood is one
of the naturally occurring materials that contributes towards reducing the carbon footprint of the building
and has structural strength similar to concrete and steel.

Figure 1-1 : Carbon storage and emissions for different building materials
(Pomponi et al. 2020)

1.3 Summary
An increase in the world’s population would directly lead to an increase in the construction industry. Tall
buildings will be required to accommodate the growing urban populations. The built environment has a
negative impact on the natural environment. Tall buildings can help in preventing urban sprawl and
reducing weather exposed surfaces but require more materials for construction and for structural stability,
and thus increase the embodied carbon footprint of the building. Since operational carbon of the building
6

can be optimized by employing efficient building envelope strategies and using energy efficient HVAC and
lighting systems, the embodied carbon of the building needs to be addressed. The embodied carbon of the
building cannot be reduced once the building is constructed, and therefore, needs to be addressed earlier in
the design stages before the construction begins. One of the most efficient ways to reduce the embodied
carbon of the building is by using low-carbon materials. Wood is a naturally occurring, low-carbon material.
It sequesters carbon and requires less energy for processing than other conservative materials. In addition
to this, wood also has comparable structural strengths to concrete and steel. The low-destiny of the material
makes it a good material for long-span and tall construction. The use of wood in construction and tools for
evaluating embodied carbon are discussed in Chapter 2.

7

2. LITERATURE REVIEW
The chapter discusses the material properties of wood, the use of timber in the construction industry,
different timber structural systems and the environmental impact of timber construction. Different methods
of embodied carbon assessments, limitations of the current methods, embodied carbon assessments of
timber products, the use of building information modeling (BIM), and tools for embodied carbon evaluation,
including the Embodied Carbon in Construction Calculator, are also discussed in the chapter.

2.1 Wood as a building material
A brief description of the properties of wood is important to understand the growing interest in using timber
for construction. Wood, a naturally occurring material, is one of the most commonly used materials. This
versatile material has many uses, from making small objects like furniture pieces to making buildings.
Wood is a natural fiber composite comprising of long cellulose fibers in a lignin matrix (Figure 2-1). A
composite material uses fiber as reinforcements (cellulose fibers in wood) within a spongy matrix (lignin).
The continuity of the fibers and the matrix is important for the strength of the material. Wood is primarily
composed of cellulose and hemicellulose (75%), followed by lignin (approx. 25%) which gives wood its
strength (Ramage et al. 2017). Wood as a material has good environmental, structural, and thermal
properties. Its propensity to fire is one of its main disadvantages. It is also highly hygroscopic, resulting in
expansion when the moisture content in the air is high and contraction when it is low. It also attracts wood-
destroying pests.

8

Figure 2-1 - Constituents of wood
(Friedman n.d.)

2.1.1 Environmental properties
Wood is a naturally occurring material; it uses energy from the sun to grow, unlike other materials like
concrete and steel that require fossil fuel as the primary source of energy for manufacturing (Falk 2009).
The amount of energy-based processing required for wood is lower than that required for other construction
materials, significantly reducing its embodied carbon footprint (Falk 2009). Wood has the ability to
sequester carbon, resulting in a lower carbon footprint (Falk 2009).

Young’s modulus, an important material structural property, is a measure of the stiffness of a material
(ZeeMa, Sobernheim, and Garzon 2016). Materials with higher Young’s modulus are stiffer and have low
elastic deformations under a given load (ZeeMa, Sobernheim, and Garzon 2016). Materials with a Young’s
modulus similar to that of wood (red dot) have higher embodied energy than wood (Figure 2-2). Wood is a
sustainable building material with relatively good structural properties as well. It can also be easily made
into prefabricated components offsite, making it easier to work with and reducing the construction time and
the associated carbon emissions (Woodard and Milner 2016).

9

Figure 2-2 - Embodied energy and Young’s modulus of wood as compared to concrete and steel
(CES EduPack 2019, ANSYS Granta © 2020 Granta Design)

2.1.2 Structural properties
Wood is widely used as a construction material in several countries (Ramage et al. 2017). It was more
commonly used for small scale construction, but with advents in technology, wood can be used for the
construction of taller buildings (Ramage et al. 2017). This is possible because of the inherent strength of
the material in comparison to its weight (Heritage Builders Ltd 2020). The strength of wood is different
along the grains and across the grains. Wood is two to five times stronger along the grain than across it
(Forest Products Laboratory 2010). Wood is better at compression than at tension, approximately 30%
stronger in compression (Forest Products Laboratory 2010). The strength of wood along its grain (red dot)
is higher than that across its grain (yellow dot) (Figure 2-3). While its strength along the grain is similar to
that of reinforced concrete, wood cannot achieve strengths as high as that of modern high-strength concrete
(Ramage et al. 2017). Wood is neither as stiff nor as strong as steel (Figure 2-3). Wood is a low-density
10

material, making it a good material for long span or tall construction where self-weight is the major load
on the material (Ramage et al. 2017). However, steel and concrete are needed to supplement the strength
of wood to resist lateral loads independent of the structure weight, like wind loads (Ramage et al. 2017).

Figure 2-3 - Strength and density of wood as compared to steel and concrete
(CES EduPack 2019, ANSYS Granta © 2020 Granta Design)

2.1.3 Thermal properties
Wood, being a porous material, exhibits low thermal conductivity, and therefore, has better insulating
capacities as compared to concrete and steel (Tsoumis 2020). The thermal conductivity of wood is lower
than that of steel and concrete, while its yield strength, which is the stress at which a material ceases to
deform elastically and starts to deform plastically, is comparable to that of these materials (Figure 2-4)
(Abdewi 2017). The thermal behavior of wood is dependent on various factors like its density, moisture
content, grain direction, and temperature (Forest Products Laboratory 2010). The thermal conductivity of
wood increases with an increase in the moisture content, density and temperature and is higher along the
11

grain than across it (Forest Products Laboratory 2010) . The thermal expansion coefficient of wood, which
is the measure of the change in the physical dimension of the material with temperature, is higher than steel
and concrete (Figure 2-5). This is because wood expands on heating and contracts on cooling. The thermal
coefficient of expansion is sometimes a problem that should be considered, especially in the design of
detailing and joints.

Figure 2-4 - Thermal conductivity and yield strength of materials
(CES EduPack 2019, ANSYS Granta © 2020 Granta Design)

12

Figure 2-5 - Thermal conductivity and thermal expansion
(CES EduPack 2019, ANSYS Granta © 2020 Granta Design)

2.1.4 Fire properties
Wood is highly susceptible to fire. This is one of the biggest limitations of using wood as an exposed
building material. Wood is composed mainly of cellulose, which is made up of hydrogen, oxygen, and
carbon atoms. When wood is ignited, these molecules break down to form flammable gasses and combine
with the oxygen in air to start a fire (Pandey et al. 2017). However, once the outer layer of wood burns, a
layer of carbon is formed on its surface. This layer acts as an insulation layer and delays the heating of the
inner layers (Pandey et al. 2017). Therefore, even though wood is highly vulnerable to fire, it has inherent
properties to control the fire as well. This understanding helps designers and engineers select the correct
size of wood such that in case of a fire, the cold wood core is still able to withstand the loads acting on the
structure (Figure 2-6).

13

Figure 2-6 - Combustion of exposed wood
(Gerard, Barber, and Wolski 2013)

2.1.5 Moisture content
Wood is a hygroscopic material; it absorbs water and expands when the moisture content in the air is high
and contracts when the moisture content is low (Friedman n.d.). This results in physical distortion of the
material. Freshly harvested wood or green wood has a high moisture content and needs to be dried before
it can be used (Ramage et al. 2017). Uncontrolled drying of wood can cause the material to warp, bow,
twist or bend (Forest Products Laboratory 2010). High moisture content in wood can make it highly
vulnerable to fungal degradation. To avoid this from happening, wood must have no more than 20% of
moisture content (Ramage et al. 2017). The moisture content should by only 8% for interior uses and 12%
for exterior uses (Ramage et al. 2017). This requires careful detailing as well.

14

Table 2-1 - Advantages and Disadvantages of wood
Material Property Advantage Disadvantage

Environmental
Sequesters carbon, low embodied
carbon
Depletes forest carbon sink if
unsustainably harvested
Structural
Low density, good for self-weight
structures, good compressive
strength
Cannot compete with the stiffness and
strength of steel
Thermal
Porous material, has low thermal
conductivity
Has a relatively higher thermal
expansion coefficient, as compared to
concrete and steel
Fire
Forms a thick layer of charcoal
which delays further heating of the
inner layers
Susceptible to fire
Moisture
With moisture content less than
20%, fungal decay and physical
distortion can be avoided
Hygroscopic, susceptible to fungal
decay

2.2 Timber construction
Timber construction dates back over 7000 years. The well of Altscherbitz, near Leipzig, is one of oldest
standing timber structures, built over 7000 years ago (Woodard and Milner 2016). The Horyuji Temple in
Nara, Japan, is a timber temple built over 1400 years ago (Woodard and Milner 2016). With a current focus
on sustainable buildings, timber is emerging as a low carbon construction material. The two main types of
timber framing are light timber framing and heavy timber framing (Gerard, Barber, and Wolski 2013). Light
timber buildings use timber for small elements like joists and studs of the building and are not higher than
6 stories (Gerard, Barber, and Wolski 2013). On the other hand, heavy timber buildings use timber for
structural elements like beams and columns and can rise over 8 stories (Gerard, Barber, and Wolski 2013).
Heavy timber refers to solid wood sections and engineered timber.

2.2.1 Engineered timber
Wood from trees can be classified into two categories: softwood and hardwood. Softwood is obtained from
gymnosperm trees, like pine, Douglas fir and cedar, while hardwood is obtained from angiosperm trees like
beech, oak, and balsa (Ramage et al. 2017). Softwood typically has a lower density, is lightweight, easy to
15

use, and grows faster than hardwood (Ramage et al. 2017). Softwood is, therefore, preferred for
construction. To enhance the structural properties and durability of wood, it is processed to create
engineered timber by gluing and bonding different types of layers or lamellae of wood together (Ramage
et al. 2017; Foster and Ramage 2020). These lamellae are classified into three categories- one-dimensional
fibers and strands, two-dimensional sheets and three-dimensional sawn boards (Foster and Ramage 2020).

The type of engineered timber products depends on the type of lamellae used. Oriented strand board and
parallel strand lumber are made using fibers or strands; laminated veneer lumber and cross laminated veneer
lumber is made from sheets and glued laminated timber, nail laminated timber and cross laminated timber
is made using sawn boards (Figure 2-7). Of these products, glued laminated timber and cross laminated
timber are used more than the other products (Barber 2015). Cross laminated timber involves layering of
solid wood panels in perpendicular directions. This makes the timber structurally sound as the grains now
run in both the directions. Glue laminated timber also increases the strength of timber by layering laminates,
usually 20-50mm thick, together (Woodard and Milner 2016). However, unlike CLT glue laminated timber
layers the panels in the same direction. This also increases the strength and stiffness of the material
substantially and enables the production of longer spanning wooden members. Glulam is widely used for
columns and beams, whereas CLT is commonly used for walls and floors (Foster and Ramage 2020).

16

Figure 2-7 - Structural engineered timber products
(Ramage et al. 2017)

Freshly harvested wood, known as roundwood, has a high moisture content. An important step of
processing wood is drying it to remove the excess moisture. The harvested wood is first processed to remove
surface defects at a sawmill (Ramage et al. 2017). Different timber products are yielded using different
methods (Figure 2-8). The logs can then either be sawed and dried to make timber planks, which are used
to make different engineered timber products like glulam, cross laminated timber, etc., or can be peeled
into smaller and thinner veneers to make plywood, laminated-veneer panels and lumber, etc., or can be
made into even smaller pieces which are used to make different timber boards (Ramage et al. 2017).

17

Figure 2-8 - Engineered timber manufacturing processes
(Ramage et al. 2017)

2.2.2 Timber structures
The structure of the building is one of the largest contributors of the embodied carbon footprint of the
building (Skidmore, Owings & Merrill 2013). The use of a low-carbon material, like wood, can reduce the
net embodied carbon footprint of the building. The availability of engineered timber products has made it
possible to use timber as a construction material for tall towers. Towers higher than 165 feet (50 meters) or
with 14 or more stories are typically considered tall structures, while buildings with heights greater than
984 feet (300 meters) and 1,968 feet (600 meters) are considered supertall and mega-tall structures
respectively (Forest, Ramage, and Reynolds 2017). The use of glulam for the primary structure with CLT
for walls and floors is the most efficient way of using mass timber products (Ramage et al. 2017). The
structural system type of a timber tower is defined by its main vertical and lateral resisting systems (Foster
and Ramage 2020). An all-timber structure utilizes timber elements to resist the main lateral loads whereas
a composite or hybrid structure utilizes a combination of materials like concrete for lateral support and a
18

timber post beam for gravity loads (Foster and Ramage 2020). An all-timber structure might not be
composed entirely of wood; the definition is reliant on wood resisting the main lateral and vertical load.

2.2.2.1 All-timber structures
All-timber structures have been used in several parts of Europe. Treet and Mjøstårnet are two such
structures. Treet, a 14-storey tower in Bergen, Norway, is an all-timber structure. It uses a partially diagonal
glue laminated timber mega-truss for resisting lateral loads (Foster and Ramage 2020). It has a CLT core
and reinforced concrete foundation (Foster and Ramage 2020). It uses a modular structural system which
comprises of glulam trusses and prefabricated residential modules that are stacked over a concrete base
(basement and lower two floors) (Foster and Ramage 2020). Power stories are used to transfer load every
five stories. To resist the high wind loads the transfer level floors and roof is topped with concrete (Foster
and Ramage 2020).

Mjøstårnet is an 18 storey, 80m tall tower in Brumunddal, Norway, built in 2018. It uses the same structural
system as Treet- glulam mega-truss with slotted-in plate and dowel connections, with RCC foundations
(Foster and Ramage 2020). Unlike Treet, Mjøstårnet does not use prefabricated modules; instead it uses
laminated-veneer panels and lumber (LVL) plate with composite glulam ribs floor to span between the
glulam beams (Foster and Ramage 2020). The top floor plates are made using concrete to resist the wind
loads (Foster and Ramage 2020).

2.2.2.2 Composite or hybrid timber structures
A composite or hybrid timber structural system is commonly used for tall timber structures. Brock
Commons Tallwood House and HoHo Wien are a few built examples. This structural system is also used
for the conceptual design of a few tall timber structures. The SOM Timber Tower Research Project is one
such proposal. Brock Commons Tallwood House is an 18-storey, 58m tall, timber structure in Vancouver,
19

Canada built in 2017. It uses a hybrid or composite structural system, with a cast-in-place reinforced
concrete core, foundation, and podium. The tower is built in a seismic zone. The RCC core and foundation
resists the wind and seismic loads. Glulam columns and two-way spanning CLT panels are used to resist
gravity loads. HoHo Wien is a 24-storey, 84m high structure in Vienna, Austria. It uses a hybrid structural
system. It has two main systems – a concrete core and a timber structure that attaches to the core (Woschitz
Group 2017). The timber structure comprises of prefabricated glulam columns, CLT floor panels topped
with concrete and CLT wall panels clad with composite fiber cement panels (Kazim 2019). Precast
reinforced concrete edge beams are used to support the floor panels (Kazim 2019). The floors are topped
with concrete to add weight to the structure and to resist wind loads (Woschitz Group 2017). The SOM
Timber Tower study is a research project wherein an existing concrete building was conceptualized using
mass timber products. The Dewitt-Chestnut building, an existing 42-storey (120m) reinforced concrete
structure built by SOM in Chicago, was redesigned using cross laminated and glue-laminated timber
structural members (Foster and Ramage 2020). The final proposal was a composite-timber structural
system. CLT shear walls cores, coupled with reinforced concrete link beams, was proposed as the lateral
load resisting system, while the gravity load resisting system comprised of CLT floor panels spanning
between the shear walls, glulam columns and RCC spandrel beams (Skidmore, Owings & Merrill 2013). A
composite timber floor with a concrete topping was used on the roof level to improve the acoustical
performance and distribute large concentrated equipment loads (Skidmore, Owings & Merrill 2013).
20

Figure 2-9 - Different structural systems
Treet (top left), Mjøstårnet (top right), Brock Commons (bottom left), HoHo Wien (bottom right)
(Foster and Ramage 2020; Woschitz Group 2017; Abrahamsen and Malo n.d.)

21

Table 2-2 - Timber structural systems
Name Location Height Structural system Structure

Treet Bergen, Norway
14 stories
(161’)
All-timber
Modular structural
system with CLT core
and glulam mega truss
Mjøstårnet
Brumunddal,
Norway
18 stories
(278’)
All-timber
Glulam mega truss with
LVL and composite
glulam floor
Brock
Commons
Vancouver,
Canada
18 stories
(190’)
Composite -timber
RCC core, with glulam
columns and CLT floor
panels
HoHo Wien Vienna, Austria
24 stories
(275’)
Composite -timber
RCC core, with glulam
columns, precast concrete
edge beams and CLT
walls
SOM timber
tower study
Chicago, USA
42 stories
(393’)
Composite -timber
CLT core with RCC link
beams and glulam
columns and RCC
spandrel beams

2.2.3 Environmental impact
Engineered timber products can be easily prefabricated and transported to the site, reducing the time for
construction and the transportation related carbon emissions (Foster and Ramage 2020). Timber structures
are lighter than conventional structures, resulting in smaller, less expensive foundations (Foster and Ramage
2020). This results in a reduction of the material quantity as well. Wood products can be reused, decreasing
the amount of material entering the waste stream. Structural columns, beams and floors can easily be reused,
as can other wood products like doors, windows, moldings, etc. (Woodard and Milner 2016). Energy
generated by burning biomass, which is yielded from end of life timber products as wood waste, can replace
the energy generated by burning non-renewable resources and the associated carbon dioxide is taken in by
the growing trees, thus closing the carbon loop (Woodard and Milner 2016). Engineered timber can yield
large structural sections from smaller diameter trees, replacing the sawn wood cross sections from larger
trees (Woodard and Milner 2016). In addition to the environmental benefits of wood, being in the presence
of a natural material can also enhance occupant satisfaction (Foster and Ramage 2020). Furthermore, since
wood is a naturally occurring material, the only energy required is the energy required for the manufacturing
22

process. The most energy intensive and important step is the drying of the roundwood (Figure 2-10). This
is usually done using a kiln. The carbon emissions can be reduced by 70% by air-drying the wood instead
of kiln-drying it (Skidmore, Owings & Merrill 2013). Mass timber products use adhesives to glue the
different layers of wood together. The use of petroleum-based adhesives results in emissions of pollutants
that have high global warming, acidification, eutrophication and toxicity potentials (Sathre and González-
García 2014). This can be prevented by using lignin-based adhesives like lignosulfonates, kraft lignin,
starch from renewable sources, animal tissue casein glues or resins made using cornstarch and tannin
(Sathre and González-García 2014). Mass timber products like CLT can be engineered to enhance their
thermal performance and thus help in reducing the operational carbon of the building (Woodard and Milner
2016).

The susceptibility of wood to decomposition reduces its durability. One of the ways to increase the
durability of timber products is by chemically treating them with wood preservatives (Sathre and González-
García 2014) . While this increases the service life of wood products and reduces the need to re-harvest
wood for the same function, it also increases the amount of toxic materials in the built environment and
limits the end-of-life use as treated wood is not as easily reused as untreated wood (Sathre and González-
García 2014). Furthermore, the growing demand for wood would mean new areas would have to be planted
with trees as the current forest area can only provide wood for 36% of the projected timber construction
(Pomponi et al. 2020). While this is a good strategy to address the future needs for the material, it is
important to address the current growing demand for timber. This demand could very easily result in
increased deforestation and illegal logging. While new trees can be planted in place of the felled trees, the
rate of extraction of wood should not exceed the rate of growth of trees (Pomponi et al. 2020). A higher
rate of extraction would deplete the world’s forests and decrease the carbon stored in the forests (Pomponi
et al. 2020). It could also damage the soil, the ground water, and forest canopies (Pomponi et al. 2020). One
of the ways to prevent over-extraction of wood from forests is to source the wood from sustainably managed
forests. A sustainably managed forest ensures that the number of trees harvested is not more than number
23

of trees that are grown (Sathre and González-García 2014). Sustainably harvesting timber from well-
managed forests sequesters more carbon than a naturally maturing forest (Ramage et al. 2017) . To ensure
sustainable extraction of wood, there are agencies that certify forests that are sustainably managed and
harvested (Ramage et al. 2017). Some of the well-known agencies in North America include the Forest
Stewardship Council (recognized for LEED certifications), Sustainable Forestry Initiative, American Tree
Farm System, Programme for the Endorsement of Forest Certification, Canadian Standards Association
(Ramage et al. 2017). The global forest area reduced by 5.2 million hectors per area, between 2000 and
2010. While some regions saw depleting forests, regions like Europe and China, by using sustainable
forestry, saw an increase in their forest area (Sathre and González-García 2014). The forest area, thus, varies
with the region, and not every region can meet the demand with their forests without disturbing the
extraction to growth ratio. This could lead to forest depletions in those regions and an increase in the amount
of timber that would need to be shipped to meet he demands. This would result in an increase in the carbon
footprint of the material.

24

Figure 2-10 - Embodied carbon emissions for different timber products
(Puettmann and Wilson 2005 as cited in Ramage et al. 2017)

2.3 Embodied carbon assessment
It is important to measure the embodied carbon of the building in order to manage and reduce it. While
measuring the operational carbon of buildings is a relatively less complicated and an easy task, measuring
the embodied carbon is time consuming and complex. (Cabeza et al. 2013). Life cycle assessment has been
around since the late 1960s (Hunt 1974 as cited in Mahamadu, Baffour Awuah, and Booth 2016). It was
first used to evaluate the impact of different packaging alternatives for Coca Cola, made its way to the oil
and manufacturing industries in the 1970s and 1980s and is now widely used to understand the impact of
the built environment (Mahamadu, Baffour Awuah, and Booth 2016). The life cycle assessment of a
building can be broken down into five stages: the product, construction process, use, end of life and benefits
and loads beyond the system boundary (Figure 2-11). Stages A1-A5 account for the carbon emissions
before building occupancy, known as upfront carbon (Waldman, Huang, and Simonen 2020). These stages
include majority of a material’s embodied carbon impact (Waldman, Huang, and Simonen 2020). A life
25

cycle assessment includes information on three categories: inventory phase, impact assessment phase and
improvement phase (Puettmann and Wilson 2005).

Figure 2-11 - Life cycle assessment stages
LCA stages and modules as per EN 15978 by the European Committee for Standardization
(Waldman et al. 2019)

Embodied carbon calculation throughout the life cycle of the building or for cradle-to-gate (product) stages
can be done using several tools like Tally, Athena Impact Estimator, One Click LCA, eTool, MMG,
SBtoolCZ, Carbon Critical Masterplanning by Atkins, Building for Environmental and Economic
Sustainability (BEES), SimaPro, etc. (De Wolf, Pomponi, and Moncaster 2017).

26

LCAs are summarized using Environmental Product Declarations (EPDs). EPDs are documents that
provide comparable data about the environmental impact of the products. EPDs are generated based on
Product Category Rules (which define the scope of the calculation) and System Boundaries (which define
which stages of an LCA are accounted for) (Sierra Club 2013). They follow standardized account methods
like ISO 21930, EN15804 etc. (Waldman et al. 2019). They provide information about various impact
categories like the global warming, ozone depletion, eutrophication, acidification and smog (Woodard and
Milner 2016). Several different types of EPDs, like industry-average EPDs, product-specific or
manufacture-specific EPDS and facility-specific EPDs, are available (Waldman et al. 2019).

2.3.1 Limitations of current embodied carbon calculation methods in the early design stage
While assessing the environmental impact of a building is helpful towards mitigating the impact of the built
environment, performing an LCA has its own challenges. Given the long lifespans of buildings and the
possibility of refurbishment and retrofitting, predicting its performance throughout its life is a challenging
task (Mahamadu, Baffour Awuah, and Booth 2016). In addition to this, the operational carbon of the
building may change, by switching to more energy efficient systems. Predicting the impact of the
operational carbon on the overall impact can thus be a difficult task. Furthermore, unquantifiable factors
that impact building performance, like occupant behavior and well-being are difficult to model for LCA,
making it hard to account for (Mahamadu, Baffour Awuah, and Booth 2016). Finally, the lack of a
standardized approach, in addition to the lack of local and accurate data, for assessing the impact makes it
a very complex task (Mahamadu, Baffour Awuah, and Booth 2016; De Wolf, Pomponi, and Moncaster
2017).

2.3.2 Embodied carbon assessment of timber products
Most EPDs use industry averages to calculate the environmental impact of a material, which can cause
inaccuracies in the embodied carbon calculation as not all material products are manufactured using the
same standards (Sierra Club 2013). Life cycle assessment of wood products can be misleading as they do
27

not take into consideration the way in which a forest is managed and harvested and the amount of wood
that is usable from trees (some research suggests only a third of the wood is usable) (Sierra Club 2013).
Once trees are harvested, they cease to act as carbon sinks (Sierra Club 2013). Wood LCAs consider that
the rate of extraction of trees is the same as the rate of growth of trees, which may not be the case for forests
that are not managed sustainably (Sierra Club 2013). Product category rules for timber product EPDs allow
the carbon sequestered in the wood to be considered for the calculations only if the end-of-life outcome for
the product is considered in the calculations (AWC and CWC 2013). The sequestered carbon is evaluated
against the emissions required for the end-of-life treatment of wood, like recycling, incinerating, etc. (AWC
and CWC 2013). As a result, most cradle-to-gate timber product EPDs do not account for the carbon
sequestered in the wood (AWC and CWC 2013).

A cradle-to-gate LCA for different timber products (e.g. glulam, laminated veneer lumber, oriented strand
board) was conducted in the Pacific Northwest and Southeast regions of the United States (Puettmann and
Wilson 2005). Embodied carbon impact during wood regeneration and harvesting, product and resin
manufacturing, and transportation to the facility was calculated based on resource and energy requirements
and emissions to water, land and air (Puettmann and Wilson 2005). The study concluded that among glulam,
kiln dried lumber, laminated veneer lumber and plywood, glulam had the highest environmental impact
(Figure 2-12). The process of drying lumber and veneer, and pressing the composite lamellae together
required the maximum amount of energy among the four processes considered. The environmental impact
of these products could be reduced by using energy efficient drying and hot-pressing techniques, alternative
feedstocks for resin production and energy efficient production techniques (Puettmann and Wilson 2005).

28

Figure 2-12 - Energy consumption for the manufacturing of timber products
(adapted with data from Puettmann and Wilson 2005)

Katerra, a CLT manufacturing company, recently conducted a cradle-to-gate life cycle analysis (stages A1-
A3) to understand the embodied carbon impact of their CLT products. The three stages accounted for the
carbon emissions caused due to forestry operations and production of wood (A1), transportation of the sawn
lumber from the sawmills to the production unit (A2) and the production of CLT at the facility (A3) (Huang
et al. 2020) (Figure 2-13). The study found that the CLT had low embodied carbon impact, between 130-
158 kg CO
2
e/m
3
, because of the use of efficient production techniques, light-weight wood species, efficient
adhesives and reduction in waste (Huang et al. 2020). The impact could be further reduced by using locally
available lumber, increasing efficiency in the procurement of CLT laminated stock to reduce material loss
and incorporating less energy intensive drying techniques like the use of hog fuel instead of natural gas
kilns (Huang et al. 2020).

0
1000
2000
3000
4000
5000
6000
Glulam KD Lumber LVL Plywood
Energy Consumption (MJ/m
3
)
Harvesting Product Manufacturing Resin Production Transportation Total
29

Figure 2-13 - System boundaries for CLT production
(Huang et al. 2020)

2.3.3 Building Information Modeling
A Building Information Model (BIM), is a three-dimensional data rich model. The model collates the
material, structural properties, cost estimates, material takeoffs, construction sequences and energy
consumption for the different components of the structure (Kensek 2014). The use of BIM can be traced
back to the 80s, when a few 3D modelling software made it possible to extract quantities and visuals from
the models (Moffat and Leitch 2014). Ever since then, more technologically advanced software like
Autodesk Revit, Trimble, Bentley etc., are used for BIM, making it easy to collaborate between different
30

trades associated with a building (Moffat and Leitch 2014). The ease of collaboration and coordination
improves the accuracy by detecting clashes before construction begins (Hall 2018). This, in turn, helps in
reducing the overall time and construction costs (Hall 2018). It also improves the construction efficiency
as fewer on-site variations are needed (Hall 2018).

BIM also facilitates environmental assessments of buildings. The calculation of embodied carbon for
buildings requires information about the materials, especially the quantities, used in the building, which
can be provided by building information models (Simonen et al., 2019). This information can be used in
stand-alone software like the Embodied Carbon in Construction Calculator and Athena Impact Estimator
for further calculations. Furthermore, the use of BIM integrated tools makes it easy to carry out life cycle
assessments of buildings (Bueno and Fabricio 2016). Tally and eToolLCD are LCA tools that work as plug-
ins for Revit, a BIM tool, enabling life cycle assessments throughout the design process (Table 2-3). The
inclusion of LCA impact categories within BIM software, like Revit, could also make environmental
assessments easier (Bueno and Fabricio 2016).

31

Table 2-3 - LCA tools
Software Tool Type
System boundary /
Design Stage Use
Calculation method Material Information 3-D model
Tally
Paid Revit plug-in;
works only in
Revit.

Cradle-to-grave:
full LCA tool; All
stages
Bases calculations on industry
averages
Exports from Revit, accounts for
all material components.
Revit model required
EC3
Free stand-alone
cloud-based tool;
Revit models can
be imported using
BIM 360
Cradle-to-gate,
considers stages
A1-A3 of the LCA;
Procurement
Uses product EPDs. Also used
to supplement LCA software
results
Material quantities are allotted
product-specific and industry
EPDs
3D model not required;
material quantities can be
entered manually
Athena
Impact
Estimator
Free Stand-alone
tool
Cradle-to-grave:
full LCA tool,
except stages B1,
B3, B5, B7 and C3;
All stages
Uses region-specific industry
averages
Can be inserted manually or can
be exported from CAD
3D model not required;
entries can be made
manually
One Click
LCA
Stand-alone, can be
used as a Revit
plug-in as well
Cradle-to-grave:
full LCA tool; All
stages
Bases calculations on country-
specific averages; has a
limited database of
manufacturer-specific EPDs
Can be exported from Revit, IES-
VE, Design Builder, Excel etc.
Requires manual entry of all the
material components
3D model not required;
entries can be made
manually without a model
Elodie
Web-based stand-
alone tool
Cradle-to-grave:
full LCA tool; also
includes health and
comfort aspects;
All stages
Uses FDES (French equivalent
for EPDs; also includes health
and comfort aspects) for
calculations
Material quantities can be
exported from BIM-model, can
also be entered manually
3D model not required;
entries can be made
manually without a model
SimaPro Stand-alone tool
Cradle-to-grave:
full LCA tool; All
stages
Uses information from LCI
databases; usually industry
averages and general
information
Material quantities can be
inserted manually, and different
processes and environmental data
can be allotted on the tool
3D model not required;
entries can be made
manually without a model

eToolLCD

Open-use, web-
based stand-alone
tool; also works as
a plug-in for Revit
Cradle-to-grave:
full LCA tool; All
stages
Bases calculations on industry
averages and generic
information
Information from the Revit model
can be imported using the plug-in
tool; information then allotted on
eToolLCD using templates from
the database
3D model not required;
entries can be made
manually without a model

32

2.3.4 Embodied Carbon in Construction Calculator

The Embodied Carbon in Construction Calculator ( EC3) tool is an embodied carbon calculation tool, which
supplements the LCA by addressing the first stage (A1-A3) of the life cycle assessment, known as the
cradle to gate stage (Waldman et al. 2019). The cradle-to-gate stages account for the majority of the
embodied carbon of the materials (Waldman et al. 2019). The tool uses product specific EPDs and industry
averages to get the embodied carbon values (Waldman et al. 2019). This enables architects and designers
to choose low carbon options by providing a comparison between different products of the same material.
It also promotes manufacturers to create EPDs for their products and find innovative methods to reduce the
carbon impact of their products (Waldman et al. 2019). Since the tool uses product specific embodied
carbon values, a more accurate analysis of the material impact can be done. For materials with fewer EPDs,
the industry average can also be considered for the analysis. However, unlike other embodied carbon
calculators like Tally that use the averages, it uses a burden of doubt approach (Waldman et al. 2019). The
higher value from the range is selected in this method, such that only 20% of the material product have a
higher EC value (Waldman et al. 2019). This enhances the accuracy of the tool.

The functional unit for embodied carbon calculation, which specifies the quantity of material, is measured
by volume (m
3
, ft
3
or yd
3
) for engineered wood products and by mass (kg or lbs.) for steel products
(Waldman et al. 2019). EPDs show the embodied carbon of the product in kilogram equivalent CO
2

(kgCO
2
e) per cubic volume (m
3
ft
3
or yd
3
)

(Huang et al. 2020). The total embodied carbon of a material in
kgCO
2
e, is calculated by multiplying the embodied carbon value from the EPDS with the material quantity
(Waldman et al. 2019).

The material quantities required in the EC3 tool for the calculations can be either entered manually or
imported from Autodesk Revit, using Autodesk BIM 360 Document Management (Waldman et al. 2019).
Autodesk BIM 360 Document Management is part of the Autodesk suite that utilizes the Autodesk cloud-
33

based technology (Autodesk 2020). The interoperability of the EC3 tool with Revit makes it easy to map
quantities from the BIM-model to the EC3 tool.

The embodied carbon impact, also known as the global warming potential analysis, is represented in the
form of a Sankey diagram (Waldman et al. 2019). A Sankey diagram is a data visualization tool that
represents energy flows and the contribution towards different energy systems (Soundararajan, Ho, and Su
2014). Each energy flow is represented in the form of arrows, the width of which is proportional to the
quantity of the flow (Soundararajan, Ho, and Su 2014). The EC3 tool uses Sankey diagrams to represent
the proportionate contribution of different materials, subassemblies and major structural assemblies of the
building towards its embodied carbon impact (Building Transparency n.d.) (Figure 2-14).

Figure 2-14 - Sankey diagram used in EC3
(Building Transparency n.d.)

2.4 Summary
Wood is a commonly used low-carbon material. It has the ability to sequester carbon and its manufacturing
processes require relatively less energy. To enhance the structural properties and durability of wood, it is
processed to create engineered timber by gluing and bonding different types of layers or lamellae of wood
together. Different engineered timber products are produced depending on the type of lamellae. Glued
34

laminated timber and cross laminated timber are commonly used for timber construction. The availability
of engineered timber has made the construction of tall timber towers possible. Timber structures are
categorized based on their lateral loading systems. A composite-timber structure uses concrete for resisting
its lateral loads and engineered timber to resist its gravity loads and an all-timber structure uses engineered
timber products to resist both the lateral and gravity loads. Several hybrid and all-timber structures have
been built around the world.

The environmental impact of the built environment can be assessed using LCA tools. Conventional LCA
methods calculate the impact of the building through all its stages- from resource extraction to its disposal.
This method is an extensive and complicated task, with several disadvantages. The EC3 tool addresses the
product stage, or the cradle-to-gate stages, of the LCA to analyze the impact of the built environment, which
is the largest contributor to net embodied carbon. Chapter 3 presents the case studies and methodology used
to investigate embodied carbon using product specific EPDs to evaluate different product options of the
same material.
35

3. METHODOLOGY
To assess the embodied carbon of timber structures, the Embodied Carbon in Construction Calculator (EC3)
tool was used. Case studies were modeled using Autodesk Revit. The information from the model was input
into the EC3 tool using BIM 360 for analysis. The case studies included different structural systems to
explore the influence of the design on the overall embodied carbon. The study took place in two stages. The
first stage evaluated how the use of the EC3 tool, which is a relatively new tool, impacted the embodied
carbon calculation for timber structures. This included a comparative study between existing embodied
carbon calculations done for a timber structure and those derived using the EC3 tool by using Product
specific Environmental Product Declarations for the same structure. The second stage of the study analyzed
the embodied carbon for a timber tower with two different structural systems for one case study and the
impact of location specific building and timber manufacturing unit on the net embodied carbon for one case
study. The method for assessing the embodied carbon was the same for both the stages of the study. The
summary of the methodology used is detailed in the sections below (Figure 3-1).

36

Figure 3-1 - Methodology Diagram

3.1 Case Study 1: Dewitt-Chestnut Apartments
The construction of tall buildings reduces the environmental impact by reducing the expansion of urban
areas. However, tall buildings use more material for construction than a low-rise building, which increases
their embodied carbon. With the aim of reducing the embodied carbon footprint of tall towers, Skidmore,
Owings & Merrill (SOM) conducted a study in 2013 to explore the use of mass timber for tall timber
structures (Skidmore, Owings & Merrill 2013). The Dewitt-Chestnut Apartment was used as a benchmark
building for embodied carbon comparisons (Skidmore, Owings & Merrill 2013). The Dewitt-Chestnut
Apartment is a 42-storey building in the city of Chicago, Illinois and was built by SOM in 1966. The
existing building has a concrete structure with a framed tube along its perimeter which is comprised of
closely spaced concrete columns, making the structure resistant to wind loads (Skidmore, Owings & Merrill
2013). The use of the framed tube resulted in lower material use and the building was used as a benchmark
37

building (Skidmore, Owings & Merrill 2013).
Table 3-1 - Benchmark building information
(Skidmore, Owings & Merrill 2013)
Location Chicago, USA
Year built 1966
Architect SOM
Height 395 feet
Number of Floors 42 ( Basement + Ground level lobby + 41 residential floors)
Floor dimensions 80’ x 124’-6”
Structural system Concrete structure with a perimeter framed tube

Figure 3-2 - Dewitt-Chestnut Building
(Skidmore, Owings & Merrill 2013)

38

3.1.1 Composite-Timber Structure
The building was redesigned as a composite mass timber structure. The main structure of the building, the
floors, shear walls and columns, were designed using mass timber products like cross laminated timber and
glued laminated timber (Table 3-3). The mass timber products were connected with concrete joints, using
steel connections. All the perimeter beams were made of concrete, for structural stability. As a result, the
building was 70% timber and only 30% concrete, when the foundation and substructure was considered
(Skidmore, Owings & Merrill 2013). When the study took place in 2013, the availability of timber products
was limited. For this reason, the report included alternative products that use less adhesive, which would
further mitigate the embodied carbon footprint and improve the indoor environmental quality (Table 3-3).
The use of glued heavy timber can reduce the adhesive use by 70% and air-dried wood can reduce carbon
emissions by 70% as compared to kiln dried wood.

Table 3-2 - Structural properties
(Skidmore, Owings & Merrill 2013)
Structural
element
Material Structural Properties

Floor
Cross Laminated
Timber
CLT, which has grains in both directions, was used for the
floors to maintain stability with changes in humidity and to
control vibrations
Columns
Glue Laminated
Timber
Glulam was considered as the material to provide the
required axial strength and stiffness
Shear Walls
Cross Laminated
Timber Panels
CLT was chosen to provide dimensional stability along the
length of the wall
Lower levels
(Up to Level 2)
RCC
RCC was chosen to increase the durability and loading
capacity of the structure
Foundation RCC 65% of the original structure required

39

Table 3-3 - Structural elements
(Skidmore, Owings & Merrill 2013)
Structural
element
Material Prototype
model
Specifications Alternative
products
Specifications

Floor Cross
Laminated
Timber
2 3-ply CLT
panels

8” thickness

5 plies of wood
instead of 6
plies.
Center member
acts as the
structural core.
The thickness
of the core
depends on the
floor thickness
1 3/8” per ply for the
bottom and top
layers.
Columns Glue
Laminated
Timber
Strength:
700psi at the
top and
1400 psi at
the bottom
32 strips of 2”
x12” machine
stress rated
wood.
Adhesive on all
faces
Glued heavy
timber columns
4 12” x12” pieces
glued together
Shear Walls Cross
Laminated
Timber
Panels
Several 3-
ply CLT
panels, with
grains
primarily in
the vertical
direction
Typical 12”,
with 3 3-ply
panels
Glued heavy
timber walls
Usually 12” heavy
timber members
glued with each
other, with 2” plies
on the outer surface
Lower levels
(Up to Level
2)
RCC
-
Concrete:
6,000 psi or
less, with low
water to
cement ratio
and plastisizers
Cement-
replaced
concrete.
Replacements
like fly ash and
ground
granulated
blast-furnace
slag are
considered
40% cement and
60% replacements
Foundation RCC Belled
caissons
foundations,
75 feet
below grade
Steel: 60 ksi

40

Figure 3-3 - Overall structure of the composite-timber structure
(Skidmore, Owings & Merrill 2013)

3.1.2 All-Timber Structure
An all-timber structure was studied as well (Skidmore, Owings & Merrill 2013). The main structural
elements, along with the link beams, were designed as mass timber elements. The use of the same structural
configuration as the composite timber structure led to an increase in the quantity of material and the floor
heights. To reduce the material quantities, and subsequently the cost of the structure, interior columns and
walls were added between the core and the perimeter. This reduced the floor panel span to 18 feet, reduced
the floor thickness to 8 inches and improved the structural performance of the structure. The use of pure
timber link beams would have resulted in very deep beams and thick shear walls. To avoid this, timber
beams with steel plates laminated within them were considered. In order to reduce the uplift caused by the
low-weight all-timber structure, shear walls were designed as mass timber walls with vertical steel plates
laminated within them. The lower levels, made using reinforced concrete and reinforced concrete belled
caisson foundations, increased the stability of the building. This structural system resulted in additional
columns and walls. The extra columns resulted in a rigid flood plan and an increase in the material quantity.
41

Figure 3-4 - All-timber structure
(Skidmore, Owings & Merrill 2013)

3.2 Case Study 2: Kanchanjunga Apartments
The Kanchanjunga Apartments are a 28-storey reinforced concrete high rise building, built by Charles
Correa, in Mumbai, India (Pagnotta 2011). The building was designed by interlocking different modules
with split levels and cantilever balconies, as a response to the Mumbai heat and rains, and to get in natural
light and ventilation (Ozkan 2009). Reinforced concrete was used for the entire structure, with an RCC
shear wall core and load bearing walls to resist lateral loads (Ozkan 2009).

Table 3-4 - Summarized information about the Kanchanjunga Apartments
Location Mumbai, India
Year built 1983
Architect Charles Correa
Height 269 feet
Number of Floors 28
Structural system Reinforced concrete structure

42

Figure 3-5 - Kanchanjunga Apartments
(Pagnotta 2011)

3.2.1 Cross Laminated Timber Structure
The Kanchanjunga Apartments were redesigned using cross laminated timber (CLT) structural members
by Aakar Design Consultants (Figure 3-7). This was done as part of the ‘CLT induction in India’ conference
organized by Aakar Design Consultants, in partnership with Mitsubishi Estate (ArchDaily 2021). The
proposed timber structure was designed using CLT members for resisting vertical loads and a concrete core
for resisting lateral loads. Steel ties were used to provide tensile strength to the timber members. These
members ran vertically and horizontally to enhance the structural performance of the building (Figure 3-6).
The timber members were connected using steel sections.
43

Figure 3-6 - Structural design of the proposed CLT structure
(Aakar Design Consultants n.d.)

The case study was selected to explore the embodied carbon impact of a location specific building. Unlike
the first case study, information about the manufacturing location of CLT, concrete, structural steel and
rebar products was available. As a result, this case study included embodied carbon associated with the
transportation of the materials from the manufacturing unit to the construction site as well. The CLT that
would be used for the building is manufactured by Mitsubishi Estate in Japan and would be transported to
the building site in India. Concrete, steel, and rebar are assumed to be manufactured locally. The
consideration of the transportation emissions was included to understand the impact of transporting mass
44

timber long distances on the net embodied carbon of the building, since mass timber is not manufactured
globally.

Figure 3-7 - Existing concrete structure (left) and CLT structure (right) of Kanchanjunga Apartments
Views taken from Revit model provided by Aakar Design Consultants (Aakar Design Consultants n.d.)

3.3 Building Information Modeling
Building Information Modeling was used to generate material information and quantities for the calculation
of embodied carbon. The structural model for each of the case studies was created in Autodesk Revit
(Autodesk 2010) and provided by the design team (Aakar Design Consultants n.d.). The structural model
included the quantity of the materials used and the material properties. Information about the structure was
extracted from the plans, sections and details of the structure from available resources. An estimate of the
45

material quantities was obtained by using the ‘material take-off schedule’ tool in Revit.

3.3.1 Material Quantity Verification
The material quantities derived from the Revit model were compared with the published estimated material
quantities from the report for Case Study 1. This was done to verify the accuracy of the model. The
published material quantities account for glued laminated timber and cross-laminated timber quantities
together. Since the EC3 tool uses product specific EPDs for calculating the embodied carbon impact, the
material quantities for both the materials had to be accounted for separately, and thus, the published material
quantities could not be used for the calculations. The rebar steel and structural steel used in the case studies,
the composite-timber structure and the all-timber structure, were not modeled in Revit. This was due to the
lack of the required information. The published quantities for these materials was used. The published
estimated material quantities were given in the unit cubic feet per square feet (Figure 3-8). The material
quantities from the Revit model were derived in cubic feet. To compare the quantities, Microsoft-Excel was
used for the calculations. The timber and concrete quantities in cubic feet from the Revit model were divided
by the total building area to get the quantity in cubic feet per square feet. The quantities were then compared.
Once the quantities from the model and the report were compared, the estimated published rebar steel and
structural steel quantities, given in pounds per square feet, were multiplied with the total building area to
get the material quantity in pounds. These quantities were then used for the embodied carbon calculation.
46

Figure 3-8 - Published estimated material quantities for composite-timber structure
(Skidmore, Owings & Merrill 2013)

Figure 3-9 - Published estimated material quantities for all-timber structure
(Skidmore, Owings & Merrill 2013)

3.4 Embodied Carbon in Construction Calculator
The Embodied Carbon in Construction Calculator (EC3) uses product-specific Environmental Product
Declarations to calculate the embodied carbon of structures (Waldman et al. 2019). The tool uses material
quantities and the embodied carbon per material from the Environmental Product Declarations (EPDs) to
calculate the embodied carbon (Figure 3-10). EC3 is a free and cloud-based software (Simonen et al, 2019).
47

The imported model in EC3 will contain all the type-families from Revit, which can be allotted EPDs for
embodied carbon calculation.

Figure 3-10 - EC3 Workflow
(Using the EC3 Tool and Transparency Catalog to Make Better Embodied Carbon Decisions. 2020)

3.4.1 Revit model to EC3
The Revit models were imported to EC3 using a BIM 360 plugin for the tool. The import transferred the
relevant information to the EC3 tool. The quantities that could not be imported from the BIM model were
manually entered in the EC3 tool from the material quantity takeoffs derived on Revit.

3.4.2 Material Information
The EC3 tool uses material take-offs from the Revit model and multiplies it with the embodied carbon of
the materials to calculate the total embodied carbon. The embodied carbon calculation in the tool can be
done using two methods. A more accurate and precise calculation can be done using EPDs of specific
products. The EC3 tool uses third-party verified EPDs for assessing the embodied carbon footprint of
48

different materials (Waldman et al. 2019). The tool currently has EPDs for 7 different materials and has a
graphical representation of the number of EPDs for each material (Figure 3-11). It also represents how
many EPDs are available from different parts of the world. The second method uses industry averages
instead of specific product information (Waldman et al. 2019). The number of product specified EPDs for
mass timber products available on the EC3 tool is very less, primarily because of the limited availability of
mass timber EDPs in the market. For materials with no relevant EPDs available on the tool, EPDs with
values closest to published data were used. EPDs are continually added to the EC3 tool. The scope of this
work will be limited to EPDs and data available up to 2020.

Figure 3-11 - EPDs in EC3 categorized by material
(Building Transparency n.d.)

3.4.3 Allotment of EPDs
For the first analysis, which involved evaluating the impact of using the EC3 tool on the embodied carbon
calculation accuracy, a range of values from the EC3 were assessed against the published results. Three
different Product-specific EPDs were selected for the analysis- product with a high, low, and mid-range
embodied carbon (Table 3-5). This was done to see how the selection of different materials impacts the
embodied carbon calculation, as compared to the published value based on industry averages.
49

For the second analysis, which accessed the embodied carbon impact of different timber structures of the
Dewitt- Chestnut apartments, EPDs with a mid-range impact were allotted to all the materials. It was
ensured that the materials in both the structures were allotted the same EPDs.

Table 3-5 - Range of values from the EPDs allotted for Analysis 1
(Building Transparency n.d.)
EPD Embodied Carbon Values

Low impact
products

Mid-range impact
products

High impact products

Concrete
(kgCO
2
e/ cubic yard)
293 349 456
Glue-laminated timber
(kgCO
2
e/ cubic yard)
112 112 329
Cross-laminated timber
(kgCO
2
e/ cubic yard)
52 112 148
Rebar Steel
(kgCO
2
e/ lbs.)
0.3 0.4 0.6
Structural Steel
(kgCO
2
e/ lbs.)
0.5 0.7 2

For the third analysis, a combination of EPDs on the EC3 tool and published data was used. The CLT was
manufactured in Japan. Japanese CLT EPDs aren’t available as CLT construction began only a few years
back in Japan (Nakano et al. 2020). Published embodied carbon impact values were used due to the
unavailability of EPDs of timber produced in Japan. According to an LCA study on the CLT production by
three factories in Japan, the cradle-to-gate impact of one cubic meter (m
3
) of CLT master board was 2.52 x
10
2

kgCO
2
e (Nakano et al. 2020). CLT EPDs on the EC3 tool with values close to the published values
were selected. While CLT was manufactured in Japan, concrete, steel and rebar were manufactured locally
in Mumbai, India. The EC3 tool does not include EPDs of Indian products in their database either. Values
of embodied carbon impact for these materials were taken from a published report (IFC 2017). The report
included a database of materials manufactured in India and their embodied carbon impact in kgCO
2
e/kg of
50

material. For materials like concrete, where the material quantity from BIM models is in volume and not
weight, the density of the material from the database was used to derive the resultant weight of the material
(Table 3-6). The resultant quantity in kgs was multiplied with the embodied carbon value in kgCO
2
e/kg to
get the overall embodied carbon impact of concrete. EPDs on EC3 with similar values were selected for the
analysis. For steel and rebar, where the functional unit of the EPDs is in either kgCO
2
e /kg or kgCO
2
e /lb.,
the values were converted to the desired unit and EPDs with similar values were selected for the analysis
(Table 3-7) (Building Transparency n.d.).

Table 3-6 - Embodied carbon calculation for concrete
(IFC 2017)
Embodied Carbon Values for Concrete
Density
(kg/m
3
)
2,200
Material quantity
(m
3
)
1,441
Material quantity
(kg)
3,170,794
Embodied carbon
(kgCO
2
e/ kg)
0.1
Net embodied carbon
(kgCO
2
e)
282,201

51

Table 3-7 - Embodied carbon values for steel and rebar
(IFC 2017)
Embodied Carbon Values for Steel and Rebar
Rebar Steel
Density
(kg/m
3
)
7,850 7,850
Material quantity
(kg)
114,841 225,864
Embodied carbon
(kgCO
2
e/ kg)
3 3
Embodied carbon for EC3
(kgCO
2
e/ lbs.)
1.2 1.3

3.4.4 Carbon Sequestration values
The EC3 tool does not account for carbon sequestered in wood for the calculations. The case studies were
compared using carbon sequestration values as well to understand the impact of carbon sequestration on
the overall embodied carbon of the structures. Published sequestered carbon values were considered for
both the case studies. The values were multiplied with the material quantities manually using MS-Excel to
get the overall impact. The results were then calculated towards the net embodied carbon of the structure.

3.5 Embodied Carbon Analysis
The embodied carbon analysis for the case studies was done using a combination of the EC3 tool and
Microsoft Excel.

3.5.1 EC3 tool
The EC3 tool uses a Sankey diagram to represent the net global warming potential of the structure. The
embodied carbon is expressed as the global warming potential and represented in kgCO
2
e. The
diagrammatic representation of the net embodied carbon of the structure shows the contribution of the
52

structural elements as well as the contribution of the individual elements to the net GWP of the structure.
The diagram evaluates the material and structure embodied carbon footprint against an EC3 baseline, which
is measured using the averages of industry-high values and industry averages, and/or EPD data (Waldman
et al. 2019).

3.5.2 Microsoft Excel
Microsoft Excel was used for embodied carbon calculations for a few materials in the second and third
analysis. The low availability of timber EPDs on the EC3 tool made it difficult to account for embodied
carbon values for CLT produced in Japan (for Analysis 3). The embodied carbon values were taken from
published research and EPDs and the calculations were carried out manually on Excel. Furthermore, the
EC3 tool does not account for carbon sequestration, as it considers the cradle-to-gate system boundaries.
For calculations that required carbon sequestration, Excel was used to perform the calculations. The
material quantities collected from the Revit model were multiplied manually with the embodied carbon
values from the published data.

3.6 Comparative Analysis
Once the embodied carbon calculations were done, the results of the studies were compared and analyzed
on Microsoft-Excel (MS-Excel), using bar graphs as the visual tool to show comparisons.

3.6.1 Existing study embodied carbon calculations
An embodied carbon analysis was done by SOM as part of the study, in order to compare the impact of the
construction materials used for the benchmark (existing Dewitt-Chestnut building) and composite-timber
building (Skidmore, Owings & Merrill 2013) (Figure 3-12). The embodied carbon calculation done by the
team took into consideration the ability of wood to sequester carbon and the construction-related carbon
emissions (Skidmore, Owings & Merrill 2013). Two embodied carbon analysis were done in the study. The
53

first considered the standard materials for the timber structure, while the second scenario considered more
sustainable options like air-dried wood and concrete with cement replacements. The construction emissions
for both the scenarios were estimated to be 16 lb. CO
2
e/sf (Skidmore, Owings & Merrill 2013). The
embodied carbon was calculated by using material estimates and CO
2
equivalent values for the materials.
The embodied carbon was measured in CO
2
e lb./sf and the material quantities were measured in cuft/sq.
The results were compared to the existing Dewitt-Chestnut Apartment, which was constructed using
concrete (Figure 3-13). The use of timber as the primary construction material substantially reduced the
amount of concrete and steel in the design. This reduced the embodied carbon of the structure. Furthermore,
the carbon sequestration of wood reduced the net embodied carbon of structure. The use of more sustainable
material options decreased the carbon footprint even further.

Figure 3-12 - Embodied carbon comparison between benchmark and composite-timber structure
(Skidmore, Owings & Merrill 2013)

54

Figure 3-13 - Embodied carbon comparison between benchmark and composite-timber structure using sustainable
options
(Skidmore, Owings & Merrill 2013)

3.6.2 Analysis 1- Embodied carbon calculation methods
The first analysis was carried out to evaluate the impact of using the EC3 tool for embodied carbon
calculation on its accuracy. This was done by comparing the results derived from the EC3 tool with the
published results from the tall timber report for the composite-timber structure of the Dewitt-Chestnut
Apartments. An envelope of values, created by selecting a range of EPDs for the materials on EC3, was
compared with the published values. The calculations of the low, mid, and high performing EPDs from
EC3 were compared with the published calculations, using bar graphs on MS-Excel.

3.6.3 Analysis 2- Embodied carbon impact of a composite-timber and all-timber structure
The second analysis, which involved a comparative study of the embodied carbon footprint of different
structural systems, was done by comparing the embodied carbon results of the composite-timber structure
and the all-timber structure of the Dewitt-Chestnut Apartments, using the EC3 tool.

55

3.6.4 Analysis 3- Embodied carbon impact of a concrete and CLT structure
The third analysis, which involved a comparative study of the embodied carbon footprint of a location
specific building, was done by comparing the embodied carbon results of the existing concrete structure
and the CLT structure of the Kanchanjunga Apartments, using the EC3 tool. The analysis included a
comparative study with and without transportation emissions, and with and without carbon sequestration to
understand the impact of these factors on the overall calculations.

3.7 Summary
The embodied carbon analysis was done using two case studies. The Dewitt-Chestnut building, an existing
concrete building, was redesigned as a composite mass timber building by SOM to study tall timber
structures. This building was selected as one of the case studies for the project. A composite-timber structure
and an all-timber structure were designed. The embodied carbon calculations of the composite timber
structure from the SOM study, which were done using industry averages, were compared to those done on
EC3 tool, which uses Product specific EPDs. Furthermore, the embodied carbon impact of the all-timber
structure was compared with that of the composite-timber structure, using the EC3 tool. The second case
study used was the Kanchanjunga Apartments, an existing reinforced concrete building, which was
redesigned using CLT structural members. This case study was a location specific study, with information
about the location of the building and the material manufacturing units available. An embodied carbon
analysis between the existing and the proposed CLT structure was done, including emissions associated
with transporting the materials from the manufacturing site to the construction site.

The embodied carbon calculation for the studies was done using Autodesk Revit and EC3 tool. Autodesk
Revit was used for creating a Building Information Model. Material quantities and properties were collated
from the model. The material quantities of the first case study were verified with the published material
quantities to verify the accuracy of the Revit models. The data from the model was then used to assign
EPDs in EC3 tool and calculate the net embodied carbon of the structure. A set of analysis was also done
56

considering carbon sequestration values. This calculation was done manually using MS-Excel. Chapter 4
presents the results from the analyses using the EC3 tool.

57

4. RESULTS AND DISCUSSION
The results from the modelling and analysis of the case studies in Chapter 3 is presented in the following
sections.

4.1 Modelling Results
The building information model (BIM) of the composite-timber structure of the Dewitt-Chestnut
Apartments, was created in Autodesk Revit and reflects the published model in the report (Skidmore,
Owings & Merrill 2013) (Figure 4-1). The model clearly shows the structural system of the structure, the
reinforced concrete foundation and bottom two stories, the timber shear wall core, the timber columns and
floor, the concrete link beams, and the concrete floor topping on the top floor. An accurate building model
ensured material quantities were obtained with fewer inaccuracies.

Figure 4-1 - Report model (left) and Revit model (right)
58

4.1.1 Quantity Verification
The material quantities from the Revit model and the estimated quantities published in the report were
compared to verify the accuracy of the model. The calculations were carried out in Microsoft-Excel. The
composite-timber and all-timber Revit models included concrete, glue-laminated timber and cross-
laminated timber. The material quantities of these materials were calculated from the material takeoffs of
the different structural elements of the materials. Reinforcement and structural steel were not modeled in
the building information models due to a lack of detail available on individual member design. The structure
and foundation values were calculated separately.

In the composite-timber structure Revit model, 137,304 cubic feet of concrete was used, as derived from
the different structural members- beams, columns, floors and walls (Table 4-1). A material quantity of 0.31
cubic feet per square feet was calculated using the values, as compared to an estimated quantity of 0.25
cubic feet per square feet from the published report (Skidmore, Owings & Merrill 2013). There was a 24%
increase in the amount of concrete used in the model as compared to the published results. This difference
in the quantity may be attributed to the absence of steel reinforcement in the reinforced concrete elements
in the Revit model. This could have resulted in an increase in the overall concrete volume of each member,
and thus, an increase in the total volume of concrete, however this was not verified due to the lack of detail
on the steel reinforcement used in the original analysis. As an estimation, rebar volume is subtracted from
the concrete volume derived from the Revit model and the concrete volume shows a difference of only 8%.
The published results are estimated quantities, which also could be a reason for the anomalies in the
quantities. The concrete used for the foundation was also 22% higher in the Revit model than the published
results (Table 4-2). This difference in quantity could also be attributed to the absence of reinforcement in
the model or the estimated published values.

The volume of glue-laminated timber and cross-laminated timber, as derived from the different structural
members- beams, columns, floors and walls, is summarized in Table 4-1. Overall, 336,779 cubic feet of
59

timber was used in the Revit model. A material quantity of 0.75 cubic feet per square feet was calculated
using the values, as compared to an estimated quantity of 0.8 cubic feet per square feet from the published
report. There was a 6% decrease in the amount of total timber used in the model as compared to the
published results. This small difference could be because the published values were estimates and not
precise values.

The material quantities for reinforcement and structural steel were derived using the estimated published
quantity. 1.7 pound per square feet and 0.1 pound per square feet of reinforcements were required for the
structure and foundation respectively, as given in the report (Skidmore, Owings & Merrill 2013) (Table
4-3). These quantities were multiplied with the total building area to get the total reinforcement quantity.
The resultant reinforcement and structural steel quantities are summarized in Table 4-3.

60

Table 4-1 - Structure material quantity verification of the composite-timber model
Structure Material Quantities

From Revit Model Estimated published Quantities
Concrete
Floors (cuft) 28,112
Columns (cuft) 3,538
Beams (cuft) 100,831
Walls (cuft) 4,825
Total (cuft) 137,304
Quantity (cuft/sqft) 0.31 0.25
Difference: 24% more concrete in the Revit model

Glued Laminated Timber

Columns (cuft) 23,700
Beams (cuft) 6,041
Total (cuft) 29,741

Cross Laminated Timber

Floors (cuft) 233,762
Walls (cuft) 73,274
Total (cuft) 307,036

Total timber (cuft) 336,777
Quantity (cuft/sqft) 0.75 0.80
Difference: 6% less timber in the Revit model

61

Table 4-2 - Foundation material quantities verification of the composite-timber model
Foundation Material Quantities

From Revit Model Estimated published Quantities
Concrete
Total (cuft) 47,020
Quantity (cuft/sqft) 0.11 0.09
Difference: 22% more concrete in the Revit model

Table 4-3 - Reinforcement and structural steel quantity calculation for the composite-timber model
Material Quantities

Estimated published
Quantities
Quantity considered
Reinforcements
Structure (lbs./sqft) 1.7
Structure (lbs.) 760,337
Foundation (lbs./sqft) 0.1
Foundation (lbs.) 44,726
Total (lbs.) 805,063

Structural Steel
Quantity (lbs./sqft) 0.3
Total (lbs.) 134,177

The timber and concrete quantities for the all-timber structure from the Revit model are summarized in
Table 4-4. A material quantity of 0.09 cubic feet per square feet of concrete and 1.10 cubic feet per square
feet of timber was calculated using the values. The published material quantities were 0.07 cubic feet per
square feet of concrete and 1.22 cubic feet per square feet of timber (Skidmore, Owings & Merrill 2013).
The concrete quantity derived from the Revit model was 28% higher than the published results, while the
timber quantities were 9% lower than the published results. The absence of the reinforcements in the Revit
model could be one of the main causes of the difference in the concrete values. The published quantities,
62

being estimates, could also cause the difference in quantities for both the materials. The material quantities
for reinforcement and structural steel were derived using the estimated published quantity. 0.4 pound per
square feet of reinforcements and 0.7 pound per square feet of structural steel were required for the structure,
as given in the report (Table 4-5). These quantities were multiplied with the total building area to get the
total steel quantity and are summarized in Table 4-5 .

The difference in the material quantities between the Revit model and published report could be avoided
by modelling accurately the reinforcement required and the steel connections between timber elements.
This difference is accounted for in the calculations by considering a range of values for the composite-
timber structure, instead of just the derived values. This would help understand the extent of impact a
change in material quantities would have on the calculations carried out by the tool. For instance, for the
composite-timber structure, the embodied carbon calculations for concrete were carried out for a quantity
of 0.31 cuft/sqft (Revit model value), 0.28 cuft/sqft and 0.25 cuft/sqft (estimated published quantity) of
material. These results are discussed in Section 4.2.1.

63

Table 4-4 - Structure material quantities verification of the all-timber model
Structure Material Quantities

From Revit Model Estimated published Quantities
Concrete
Floors (cuft) 20,111
Columns (cuft) 3,537
Beams (cuft) 10,704
Walls (cuft) 4,825
Total (cuft) 39,177
Quantity (cuft/sqft) 0.09 0.07
Difference: 28% more concrete in the Revit model

Glued Laminated Timber

Columns (cuft) 34,285
Beams (cuft) 118,503
Total (cuft) 152,788

Cross Laminated Timber

Floors (cuft) 233,762
Walls (cuft) 106,504
Total (cuft) 340,266

Total timber (cuft) 493,055
Quantity (cuft/sqft) 1.10 1.22
Difference: 9% less timber in the Revit model

64

Table 4-5 - Reinforcement and structural steel quantity calculation for the all-timber model
Material Quantities

Estimated published
Quantities
Quantity considered
Reinforcements
Structure (lbs./sqft) 0.40
Total (lbs.) 178,903

Structural Steel
Quantity (lbs./sqft) 0.70
Total (lbs.) 313,080

4.2 Analysis 1 – Embodied carbon calculation methods
The first analysis was to understand the impact of using the Embodied Carbon in Construction Calculator
tool on the accuracy of embodied carbon calculation in early design stages. The embodied carbon
calculation results from the EC3 tool were compared with the published embodied carbon calculations of
the composite-timber structure of the Dewitt-Chestnut Apartments. The EC3 tool uses product specific
EPDs to evaluate the embodied carbon impact of the material, whereas the published results utilized
industry averages to assess the impact.

4.2.1 Embodied carbon calculations using EC3 tool
Several calculations were carried out for the composite-timber structure of the case study. A set of
calculations were done using a range of material quantities to understand the extent of impact of material
quantity change on the overall embodied carbon calculations. This was done to understand how the
difference in the material quantities between the Revit model and the report impact the calculations. The
next set of calculations used the material quantities derived from the Revit model and a range of EPDs.
Three different EPDs, with high, low, and average embodied carbon products, were used to establish a
range of values to compare with the published calculations (Table 3-5). The embodied carbon impact of a
65

building is represented in the form a Sankey diagram in the EC3 tool (Figure 4-2). The given Sankey
diagram shows the embodied carbon impact of the composite-timber structure, when assigned EPDs with
average embodied carbon values. The diagram shows the relative contribution of all the materials, concrete,
timber, reinforcements, and structural steel, towards the whole building embodied carbon. The solid color
on each bar represents an achievable value, indicating the availability of products of the same material with
lower embodied carbon impact that the selected product. Each line represents the embodied carbon value
for the selected product, and the top of the bar shows the conservative high value of the impact. The diagram
also shows the impact of each structural member and their relative material quantity. For example, each
arrow leaving the concrete column shows the relative contribution of the different structural members
towards the material. The right-most bar shows that a 45% reduction could be achieved by using products
with the lowest embodied carbon impact and compares that against the overall impact using the selected
products and the conservative high impacts if high-carbon products were selected. This diagram helps in
identifying materials and structural elements that have high impacts and understand the overall performance
of the building.

Figure 4-2 - Sankey diagram for composite-timber structure with mid-range EPDs

66

An envelope of material quantities was considered to account for the differences in the material quantities
between the Revit model and published values (Figure 4-3). The quantity of timber was less in the Revit
model in comparison to the published reports, while the volume of concrete was higher in the model than
in the published reports. The embodied carbon impact reflects this, with the impact being more for concrete
for the Revit model values and low for timber. The difference in impact of concrete is more than that of
timber because of the low embodied carbon impact of timber in comparison to concrete. The total building
impact is not significantly affected by the inaccuracies in the material quantities; the total embodied carbon
in kgCO
2
e was 9% lower based on the published LCA values compared to the Revit values (Figure 4-4).
The tool, therefore, could be used for early assessments. However, to ensure complete accuracy of results,
precise quantities should be used. For this reason, the use of the EC3 would be ideal in the stages of
construction where accurate material quantities are available instead of estimates.

Figure 4-3 - Impact of material quantity change on embodied carbon calculations

67

Figure 4-4 - Comparative overall impact

4.2.2 Embodied Carbon Calculation Verification
The EC3 is a relatively new tool. The calculations done on the tool were verified by manually carrying out
calculations for the same values. For the verification, the composite-timber structure was used with mid-
range value EPDs. The calculations done manually on MS-Excel match those done by the EC3 tool (Table
4-6). For example, for concrete, the embodied carbon in kgCO
2
e/cubic yards is 349 for the selected EPD,
resulting in a total impact of 2.38M kgCO
2
e. This value matches the one calculated using MS-Excel. The
total building calculated by EC3 was 4.23M kgCO
2
e, which matches the total impact calculated on MS-
Excel.

68

Table 4-6 - Embodied carbon values on Excel and EC3 tool

Material
Quantities
(cuft)
Material
Quantities
(cubic yard)
kgCO
2
e / cubic
yard
or
kgCO
2
e / lbs.
Total impact
in EC3
(Million
kgCO
2
e)
Total impact
in Excel
(Million
kgCO
2
e)
Concrete 184,324 6,827 349 2.4 2.4
Glulam 29,741 1,102 112 0.1 0.12
CLT 307,036 11,372 112 1.27 1.27
Rebar (lbs.) 805,063 0.4 0.33 0.34
Structural
Steel (lbs.)
134,177 0.8 0.10 0.11
Total 4.23 4.22

4.2.3 Comparative analysis with study results
The embodied carbon impact of each material and the whole building using the EC3 tool was compared to
the published embodied carbon results of the composite-timber structure (Skidmore, Owings & Merrill
2013). Three values for each material were compared from the EC3 tool with the LCA results. These results
were also compared with the benchmark building, the existing Dewitt-Chestnut building to understand the
difference in impact between a structure made using conventional materials and one made using timber.
The analysis shows how different products from EC3 (yellow bar) fair against the industry average (blue
bar). In the first case, most of the materials from the EC3 tool have a lower impact than the industry averages
(Figure 4-5), whereas in the last case, all the materials from the EC3 tool have a higher impact than the
industry average (Figure 4-7). This shows that an industry average does not provide a clear picture of the
material impact. It is highly likely that the selected material product could have an impact higher than the
assumed industry average value, which could lead to inaccurate overall calculations. The use of specific
impact values, as provided by product specific EPDs in the EC3 tool, can increase the accuracy of
calculations.

69

Figure 4-5 - Comparative analysis with low-impact EPDs

70

Figure 4-6 - Comparative analysis with mid-impact EPDs

Figure 4-7 - Comparative analysis with high-impact EPDs
71

4.2.4 Carbon Sequestration
One of the main differences in the published calculations and EC3 calculations is the embodied carbon
impact of timber. The published calculations have a net negative impact for timber, while the EC3 values
are positive. This is because the published calculations, which use industry averages, account for the carbon
sequestered by the mass timber elements, while EC3 does not consider carbon sequestration. The EC3 tool
considers the environmental impact of a material from the cradle-to-gate stages. As discussed in Section
2.3.2, product category rules for timber product EPDs allow the carbon sequestered in the wood to be
considered for the calculations only if the end-of-life outcome for the product is considered in the
calculations (AWC and CWC 2013). The sequestered carbon is evaluated against the emissions required
for the end-of-life treatment of wood, like recycling, incinerating, etc. (AWC and CWC 2013). As a result,
most cradle-to-gate timber product EPDs do not account for the carbon sequestered in the wood (AWC and
CWC 2013). The published results use industry averages that do not have these restrictions.

The issue of carbon sequestration is an important one. The ability of wood of absorb carbon from the
atmosphere throughout its life is one of the biggest advantages of the using the material for construction. A
timber product locks the carbon stored in the material till the end of its life, after which it re-releases the
stored carbon back into the atmosphere (Pomponi et al. 2020). A tree, unlike a timber product, would
continue to absorb carbon throughout its life. Forests create a carbon sink, and if a felled tree is not replaced
by another tree, a deficit in the carbon sink would be created (Pomponi et al. 2020). This would adversely
affect the environment, making wood an ineffective material for reducing the carbon footprint. Therefore,
the carbon sequestered in a timber product should be accounted for when a clear picture of its end of life
uses is present and the harvesting practices are sustainable. The EC3 tool provides a more conservative
value, without accounting for the sequestered carbon. This could be useful method in early design stages
or in situations where the end of life use and forestry practices are not considered, as it could avoid
misleading results of the carbon footprint of the building.

72

To understand the impact of carbon sequestration on the timber embodied carbon, the published timber
values were back calculated, and a set of sequestered values were subtracted from the net embodied carbon
values of timber. This pointed out the impact of timber without carbon sequestration. Two different values
of sequestered carbon were used for the calculation, one that was used in the published SOM report and
one value from the North American Lumber report. The SOM published report considered a sequestered
carbon value of 891 kgCO
2
e/m
3
and did not account for any end of life emissions (Puettmann and Wilson
2005). The North American Lumber report reported a value of 795 kgCO
2
e/m
3
of sequestered carbon and
312 kgCO
2
e/m
3
of end of life emissions (Table 4-7). These values were subtracted from the net negative
embodied carbon of timber reported in the published report. This calculation showed that if the sequestered
carbon of the timber was not accounted for, it would have had a very high embodied carbon (Figure 4-8).
This would impact the overall embodied carbon footprint of the building. Furthermore, there are differing
values for the carbon sequestered in wood and different results can give different and misleading results.
Therefore, the use of a conservative value avoids these inaccuracies and provides a clear picture when
precise carbon sequestration and end of time emission values are not known.

Table 4-7 - Carbon sequestration values

SOM report values North American Lumber report
Timber quantity (cuft/sqft) 0.8 0.8
Timber quantity (m
3
) 10,132 (357,806 cuft) 10,132 (357,806 cuft)
Sequestered Carbon (kgCO
2
e/m
3
) 891 795
End-of-life treatment emissions
(kgCO
2
e/m
3
)
0 312
Total sequestered carbon (kgCO
2
e) 9,025,079 (9M) 4,894,263 (4M)
Total embodied carbon (kgCO
2
e) 7,996,387 (8M) 3,865,571 (3M)

73

Figure 4-8 - Comparative analysis without carbon sequestration

4.2.5 Summary of Analysis 1
The first analysis, which was done to understand the accuracy of using product specific EPDs, showed that
the EC3 tool provided a more clear and precise calculation than industry averages. The material quantities
of the composite timber structure had a few differences between the estimated published quantities and
those derived from Revit. The difference in the quantities was because the reinforcements were not modeled
in the concrete sections in the Revit model and because the published values were estimates and not precise
values. These minor differences in the material quantities did not impact the calculation on the EC3 tool
significantly. However, an ideal use for the tool would be when accurate material quantities are available.
A comparison between the published embodied carbon values and the EC3 values showed that the values
from EC3 provided a clear and accurate picture, as the tool gave precise values which ensured that the
material would not perform worse than the considered value. The inclusion of sequestered carbon in wood
is a debatable topic within the field (Pomponi et al. 2020). The consideration of the sequestered carbon has
a significant impact on the calculations, however, there are no established values for carbon sequestration.
Furthermore, the scope of the analysis (e.g. end of life treatment emissions and forestry practices) also
74

impact the carbon sequestration value. Therefore, without having accurate information about the forestry
practices and end of life treatments of the wood used, inclusion of carbon sequestration results in uncertainty
in the analysis. The use of the EC3 tool provides a conservative analysis with reduced uncertainty.

4.3 Analysis 2 – Embodied carbon of composite-timber and all-timber structures
The second analysis was to understand the embodied carbon impact of different timber structural systems.
The composite-timber structure, which uses a combination of mass timber, steel and RCC for the structure,
and the all-timber structure, which uses mass timber and steel for the structure, of the Dewitt-Chestnut
Apartments were considered for the analysis. EPDs with mid-range impact were considered for the
calculations.

4.3.1 Embodied carbon of composite-timber structure
The first analysis for the embodied carbon impact of the composite-timber structure was done using the
EC3 tool. The output from the EC3 tool was in the form of a Sankey diagram, as discussed in Section 4.2.1.
The embodied carbon analysis using mid-range EPDs highlights the high embodied carbon impact of
concrete, as compared to timber, towards the whole building embodied carbon (Figure 4-2).

4.3.2 Embodied carbon of all-timber structure
The embodied carbon assessment of the all-timber structure was carried out on EC3. The resultant
embodied carbon is represented in the form of a Sankey diagram (Figure 4-9). The diagram shows that the
overall impact of cross-laminated timber (top, left-most green bar) is higher than that of concrete (second
left-most blue bar), followed by glue-laminated timber (third left-most orange bar). This is because the
timber quantity increases by 46% in the structure, while the concrete quantity reduces by 71%. The
embodied carbon impact of timber increases by 46% and that of concrete reduces by 53%.

75

Figure 4-9 - Embodied carbon impact of the all-timber structure

4.3.3 Comparative analysis between the structural systems
The net embodied carbon results of the composite-timber and all-timber structure were taken from EC3 to
MS-Excel for comparison. The comparative analysis between the two structures show that the embodied
carbon impact of steel and timber increases in the all-timber structure by 130% and 46% respectively. This
is because as the quantity of timber increases, the amount of steel required to connect the timber members
together increases. The concrete and the rebar embodied carbon impact is lower than the composite-timber
structure by 53% and 73% respectively. Overall, the net embodied carbon impact of the all-timber structure
is lower than that of the composite-timber structure (Figure 4-10). However, the difference, 17.5%, is not
significant. The net embodied carbon of the all-timber structure shows a reduction by less than 1 million
kgCO
2
e.

One of the disadvantages of using an all-timber structure is organizational rigidity as more timber structural
members are required for structural stability (Figure 4-11). A small reduction in the overall embodied
carbon may not justify the organizational rigidity. Furthermore, the calculations do not account for the
76

emissions associated with transporting the materials from the manufacturing unit to the site of construction
and could result in an increase in the net embodied carbon of the all-timber structure.

Figure 4-10 - Comparative analysis between the embodied carbon impact of the structures

Figure 4-11 - Structural layout of composite-timber (left) and all-timber (right) structures

77

4.3.4 Carbon sequestration
The embodied carbon results from the EC3 tool did not account for the carbon sequestered by wood. This
was because of the limitations of the EC3 tool system boundaries and the lack of information about forestry
practices and end-of-life treatments, as discussed in Section 4.2.4. A set of calculations was done for both
the structures with inclusion of carbon sequestration to understand the impact of sequestered carbon on
reducing the net embodied carbon of the structure. The carbon sequestration values from the North
American Lumber report are considered for this analysis, as they take into consideration end-of-life
treatment emissions as well (AWC and CWC 2013). A sequestered carbon value of 795 kgCO
2
e/m
3
and an
end-of-life treatment emission value of 315 kgCO
2
e/m
3
are considered in the report, and for this analysis
(Table 4-7). After carrying out the required calculations for the all-timber structure, a net sequestered carbon
value of -6.7 million kgCO
2
e was added to the embodied carbon impact of 2.05 million kgCO
2
e, as derived
from the EC3 tool, to get the net embodied carbon impact of -4.65 million kgCO
2
e for the timber used.
Similarly, a net sequestered carbon value of -4.5 million kgCO
2
e was added to the embodied carbon impact
of 1.4 million kgCO
2
e to get the net embodied carbon impact of -3.17 million kgCO
2
e for the timber used
in the composite-timber structure.

The analysis shows that the net embodied carbon changes substantially when sequestered carbon is
accounted for. Both the structures have a net negative embodied carbon impact when carbon sequestration
is accounted for, which shows that the structures would remove more carbon than they would release in the
atmosphere (Figure 4-12). The impact of the composite-timber structure is higher than the all-timber
structure by 2.8 million kgCO2e. The analysis also shows that an increase in the timber quantity by 46%
reduces the embodied carbon impact of the building by almost 800%.An increase in the timber quantity
results in lower quantities of concrete required, and thus, a significant reduction is achieved. The all-timber
structure utilizes 71% less concrete as compared to the composite-timber structure, which also contributes
to a net embodied carbon reduction by 800% when carbon sequestration is accounted for.

78

The material impact in the all-timber structure also differs when the sequestered carbon is accounted for.
In the scenario where sequestered carbon is not accounted for, the mass timber products add to the carbon
emissions, whereas when it is accounted for, they contribute towards the net reduction of the net embodied
carbon (Figure 4-13). The use of timber for buildings, if harvested sustainably, can reduce the carbon
footprint of a building significantly. Therefore, in addition to increasing the use of mass timber for
construction, forestry practices should also be regulated, and forests managed sustainably to ensure low
carbon footprints.

Figure 4-12 - Comparative analysis with carbon sequestration

79

Figure 4-13 - Material impact comparison

4.3.5 Summary of Analysis 2
The second analysis was conducted to compare the embodied carbon impact of a composite-timber structure
and an all-timber structure. Analysis using the EC3 tool showed that the all-timber structure has a lower
embodied carbon impact than the composite-timber structure, even though the carbon sequestered by wood
was not included in the analysis. There was an increase in the contribution of both mass-timber and steel
towards the net embodied carbon in the all-timber structure. The difference in the net embodied carbon
between the two structures was not significant, with the all-timber structure performing better by less a
million kgCO
2
e. These calculations did not account for the emissions associated with the transportation of
the timber products from the manufacturing unit to the site of construction as well, which would further
increase the embodied carbon impact of the all-timber structure. When the carbon sequestered in wood is
included in the calculations, the results change significantly. The composite-timber structure has an
embodied carbon impact of -0.35 million kgCO
2
e and the all-timber structure has an impact of -3.21 million
kgCO
2
e. This shows that with the correct forestry practices, timber can be used for construction to
significantly reduce the carbon footprint of the building. Timber, as compared to a concrete structure, would
still have a lower embodied carbon impact even if sequestered carbon is not considered and, therefore, its
use must be encouraged to reduce the impact of the built environment on the natural environment.
80

Table 4-8 - Embodied carbon impact change between the composite-timber and all-timber structure

Embodied carbon impact
Concrete 53% reduction in the all-timber structure
Rebar 73% reduction in the all-timber structure
Steel 130% increment in the all-timber structure
Timber without carbon
sequestration
46% increment in the all-timber structure
Timber with carbon
sequestration
46% reduction in the all-timber structure
Total building without carbon
sequestration
17.5% reduction in the all-timber structure
Total building with carbon
sequestration
800% reduction in the all-timber structure

4.4 Analysis 3 – Embodied carbon of concrete and CLT structures
The third analysis was to understand the embodied carbon impact of a location specific building, the
Kanchanjunga Apartments. The CLT used for the structural proposal was manufactured in Japan, while the
location of the building was in Mumbai, India. The other materials used, concrete, steel, and rebar, were
assumed to be manufactured locally in Mumbai. Comparative analysis between the existing reinforced
concrete (RCC) structure and the CLT structure is done for this study.

4.4.1 Material quantities
The material quantities for the calculation were taken from the Revit model of the existing concrete structure
and the proposed CLT structure. The steel and rebar quantities were estimated using published data. The
rebar quantity was approximated based on the amount of rebar (in kgs) required per cubic meter of concrete
for lateral and load bearing walls (Janicki n.d.). A value of 120kg of rebar/m
3
of concrete was assumed for
the calculations (Janicki n.d.). The steel quantity was approximated based on the quantity of steel (in lbs.)
required for one cubic feet of mass timber for all all-timber structure of the Dewitt-Chestnut Apartments.
81

The quantity derived was 0.643 lbs. of steel/ cuft of timber. The quantities thus derived were inputted in
the EC3 tool for the embodied carbon analysis (Table 4-9).

Table 4-9 - Structural material quantities
Structure Material Quantities
Existing concrete structure CLT structure
Concrete (From Revit model)
Walls (m3) 5,113 957
Floor (m3) 1,364 0
Beams (m3) 103 0
Finishes (m3) 237 484.26
Total (m3) 6,816 1,441

Rebar (From published report)
Assumed quantity (kg/m3) 120 120
Total (kg) 789,519 114,841

Cross-laminated timber (From Revit model)
Walls (m3) 0 3,405
Floor (m3) 0 2,441
Total (m3) 0 5,846

Structural Steel (From published report)
For tension cables from Revit
model (kgs)
0 166,493
Assumed Quantity
(lbs./ cuft of timber)
0 0.6
Total (kgs) 0 225,864

4.4.2 Transportation emissions
The study was location specific, and the emissions associated with transporting the materials from the
manufacturing unit to the construction site were accounted for. The CLT is manufactured in a factory in
Kyushu, Japan. The material would be transported from the port closest to Kyushu, Japan to the port in
82

Mumbai, India, where the building is located. Published values for transportation by ship and road
emissions in kgCO
2
e per tonne of material per kilometer of distance were considered (Defra et al., n.d.).
The closest port to Kyushu is the Hakata port. The distance from Kyushu to Hakata port would be covered
by road and from Hakata port to Mumbai port by sea. The distances and the associated emissions are
summarized in Table 4-10. The concrete, steel and rebar used in both the structures are locally sourced from
Mumbai and, thus, the transportation emissions for these materials are not accounted for.

Table 4-10 - Transportation emissions
Transportation Emissions
Ship Freight – General Cargo
Transportation emissions
(kgCO
2
e/tkm)
0.01
Distance between Hakata port
and Bombay port
(nautical miles)
4,935
Distance between Hakata port
and Bombay port
(km)
9,140
Timber quantity
(tonne)
5,846
Total emissions
(kgCO
2
e)
702,883
Road Freight > 17t
Transportation emissions
(kgCO
2
e/tkm)
0.2
Distance between Kyushu and
Hakata port
(km)
140
Timber quantity
(tonne)
5,846
Total emissions
(kgCO
2
e)
142,393

Total transportation emissions
(kgCO
2
e)
845,277
83

4.4.3 Carbon sequestration
Carbon sequestered in the wood is also accounted for one of the analyses. This is primarily because of the
forestry practices in Japan. Japan’s Basic Plan on Forests and Forestry defines policies and measures to
ensure sustainable forestry practices (Earth Blogs 2017). Furthermore, certifications like the Sustainable
Green Ecosystem Council (SGEC) and other third-party certifications monitor and regulate the sustainable
management of Japan’s forestry (Earth Blogs 2017).

4.4.4 Comparative analysis
Three analyses were carried out. The first analysis compared the embodied carbon impact of the existing
concrete structure with the proposed CLT structure without accounting for the transportation emissions and
the carbon sequestered, the second analysis included the transportation emissions and the last analysis
included the impact of carbon sequestration on the overall impact.

The first analysis considers two embodied carbon values for the CLT used in the timber structure. As
discussed in Section 3.4.3, published values were considered for the embodied carbon impact of CLT due
to the lack of EPDs for timber products in Japan. The closest value to the published value, 2.52 x 10
2

kgCO
2
e/m
3
, was considered on the EC3 tool. The highest embodied carbon value on the EC3 was 195
kgCO
2
e/m
3
. This value is lower than the published embodied carbon values for CLT in Japan. As a result,
both the values were considered for calculation. The analysis shows that the CLT structure performs better
than the concrete structure, with the embodied carbon impact of the concrete and rebar reducing by 79%
and 85% respectively in the CLT structure (Figure 4-14). The embodied carbon of the CLT structure is
lower than the concrete structure by almost one million kgCO
2
e (27%), when the published values are
considered, and lower by 1.3 million kgCO
2
e (36%) when the EC3 values are considered. For an accurate
analysis, the selection of the correct material product is, therefore, necessary. This highlights a limitation
of the EC3 tool. The database of the tool does not include EPDs from all countries and can result in
inaccuracies in calculations.
84

Figure 4-14 - Comparative analysis between the concrete and proposed CLT structure

The second analysis shows the impact of transporting the materials from their manufacturing unit to the site
of construction, on the overall embodied carbon footprint of the structure. The analysis shows that the
carbon footprint of the CLT structure increases by almost a million kgCO
2
e (37%) when the transportation
emissions are accounted for (Figure 4-15). While the difference in the embodied carbon impact between
the concrete and CLT structure reduces substantially, the CLT structure still performs better than the
concrete structure by 13%. This goes to show that even if timber products need to be transported long
distances, the CLT structure would have a lower carbon footprint than a concrete structure with locally
sourced materials. However, this is a location-specific assessment and would change with a change in
location of the manufacturing units and construction site.
85

Figure 4-15 - Comparative analysis with transportation emissions

The third analysis includes the carbon sequestered in the wood and compares the embodied carbon footprint
of the existing concrete structure and the CLT structure. The inclusion of sequestered carbon makes the net
embodied carbon footprint of the building negative (Figure 4-16). The CLT structure where the carbon
sequestered in the wood is considered has an embodied carbon footprint 125% lower than the CLT structure
where the sequestered carbon is not accounted for and 124% lower than the concrete structure. This
highlights the importance of sustainable forestry practices to reduce the embodied carbon footprint of
buildings.
86

Figure 4-16 - Comparative analysis with carbon sequestration

4.4.5 Summary of Analysis 3
The third analysis, which was done to understand the embodied carbon footprint of a location specific
building and manufacturing unit, highlighted the impact of emissions associated with transporting the
materials from the manufacturing unit to the construction site. All the three analyses done show that the
CLT structure performs better than the concrete structure. The CLT, which is transported from Japan to
Mumbai, increases the overall impact of the timber structure by almost 1 million kgCO
2
e. Despite the
increase in the overall impact, the CLT structure still performs better than the concrete structure. When the
carbon sequestered is accounted for, the overall impact of the CLT structure reduces by 124% as compared
to that of the concrete structure. This shows that timber can be used, even if it is not locally sourced, to
reduce the net embodied carbon footprint of the building. It also highlights the importance of maintaining
forests sustainably and ensuring that forests are not over harvested, to achieve a net-negative embodied
carbon for a building. This would result in the building taking more carbon from the atmosphere than
releasing it, which could be helpful in addressing climate change.

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Table 4-11 - Embodied carbon impact change between the concrete and CLT structure

Embodied carbon impact
Concrete 79% reduction in the CLT structure
Rebar 85% reduction in the CLT structure
Total building without carbon
sequestration
36% reduction in the CLT structure
Total building with
transportation emissions
37% increment in net embodied carbon
footprint as compared to locally sourced
CLT
Total building with
transportation emissions
13% reduction in the CLT structure
Total building with carbon
sequestration
124% reduction in the CLT structure

4.5 Summary
The two case studies explored the net embodied carbon footprint of a mass timber structure as compared
to a concrete or composite-timber structure. The first and second analyses considered the composite-timber
and all-timber structures of the Dewitt-Chestnut building. The first analysis was done to understand the
impact of the EC3 tool on the accuracy of embodied carbon calculations. The results of the analysis showed
that EC3 enhanced the accuracy of the calculations and provided precise values. The impact of difference
in material quantities on the calculations was also considered. The results showed that while a difference
of 30% or lower in the material quantities does not impact the calculations significantly, for enhanced
accuracy the tool should be used in later design stages when exact material quantities are available. The use
of the EC3 tool does not account for carbon sequestration and provides a more conservative value, which
reduces inaccuracies in overall calculations. The results of the second analysis, which was done to compare
the overall embodied carbon of the composite-timber and all-timber structures, showed that the all-timber
structure performed better than the composite-timber structure. The difference was not significant, however,
the inclusion of carbon sequestration resulted in a net negative embodied carbon for both the structures. An
increase in the timber quantity by 46% reduced the net embodied carbon of the building by 800%. This
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highlights the impact sequestered carbon of wood has on the reduction of net embodied carbon of buildings,
which signifies the importance of correct and sustainable forestry practices. The third analysis used a
location specific case study, with consideration of the location of the building and the manufacturing units
of the materials used. The Kanchanjunga Apartments in Mumbai, which was redesigned using CLT as part
of a conference, was used as the case study for this study. The results of the analysis showed that even
though the CLT was transported from Japan to Mumbai, the CLT structure performed better than the
existing concrete structure. The carbon sequestered in the wood was also accounted for, as Japan has
regulations in place for sustainable forestry practices. The net embodied carbon of the CLT structure
reduced significantly when the carbon sequestered was accounted for.

The second and third analyses show that timber as a material for construction reduces the net embodied
carbon of the building, even if the carbon sequestered by wood is not accounted for and even if the timber
product is not locally produced. Sustainable forestry practices ensure the inclusion of the carbon sequestered
by wood, which substantially reduces the net embodied carbon, resulting in a net negative embodied carbon.
Therefore, timber structures are capable of removing more carbon from the atmosphere than releasing
carbon. The observations drawn from the study and opportunities for future work are discussed in Chapter
5.

89

5. CONCLUSIONS AND FUTURE WORK
The thesis explored the impact of using product specific EPDs on embodied carbon calculations, the
embodied carbon impact of different timber structural systems, and the impact of transportation emissions
and carbon sequestration on the net embodied carbon footprint. A summary of the analyses conducted, and
future research work is discussed in the sections below.

5.1 Hypothesis 1
The first hypothesis explored the impact of using product specific EPDs on the accuracy of embodied
carbon calculations. To investigate the impact, EC3, a tool that uses product specific EPDs to calculate the
embodied carbon impact of building materials was used. The embodied carbon results from the EC3 tool
were compared with published cradle-to-gate results for the composite-timber redesigned structure of the
Dewitt-Chestnut Apartments. The comparative analysis showed that the use of EC3 provided more accurate
results, due to the use of manufacturer values rather than industry averages as used in the published study.
Furthermore, the EC3 tool uses a burden of doubt approach and considers conservative values to reduce
inaccuracies and uncertainty in the analysis. The impact of the difference in the considered and actual
material quantities on the calculations using the tool was also studied. The results suggested that while the
tool could be used for early design assessments, it would be ideal when accurate and precise material
quantities are available. In addition to this, since the tool uses product specific EPDs, it may have limitations
in early design stages where exact products for all the materials are not available. This tool could be used
for product selections once the materials of the buildings have been finalized. However, since the tool uses
the burden of doubt approach for industry averages as well, it could be used for deriving early estimates of
the embodied carbon footprint of the building. The conservative values provided by the tool could give
more accurate estimates than industry averages.

90

The EC3 tool considers the cradle-to-gate system boundary, and as a result, does not account for the
emissions associated with transporting the materials from the manufacturing units to the site of construction.
This consideration may be important, especially for mass timber, as the timber industry is still a developing
industry and mass timber products are not manufactured globally yet. The impact of transporting the timber
from another country could have a significant impact on the net embodied carbon footprint of the building,
and therefore, must be considered towards the embodied carbon calculations. The tool also does not account
for the carbon sequestered by wood for the calculations. The consideration of the sequestered carbon has a
significant impact on the calculations, however, there are no established values for carbon sequestration.
Furthermore, the scope of the analysis (e.g. end of life treatment emissions and forestry practices) also
impact the carbon sequestration value. Therefore, without having accurate information about the forestry
practices and end of life treatments of the wood used, inclusion of carbon sequestration results in uncertainty
in the analysis. The use of the EC3 tool, provides a conservative analysis with reduced uncertainty.

One limitation of the EC3 tool was its limited database. It currently includes EPDs for concrete, steel,
aluminum, wood, glass, ceiling panels, gypsum boards and carpets. While the database has a large number
of EPDs for certain materials, like concrete and steel, the number of EPDs for other materials, like timber,
is very limited. Furthermore, the database does not include products from all countries, which limits the use
of the tool. The lack of timber EPDs on the tool could be attributed to the low availability of timber EPDs
in the market. As compared to concrete and steel, timber EPDs are not as common, and an effort to generate
more EPDs for mass timber products is required.

5.2 Hypothesis 2
The second hypothesis explored the net embodied carbon impact of an all-timber structure in comparison
to a composite-timber structure. The research investigated two structural systems of the Dewitt-Chestnut
Apartments. The calculations were carried out using the EC3 tool. The comparative analysis results showed
that net embodied carbon impact of the all-timber structure was lower by 17% than that of the composite-
91

timber structure, even though carbon sequestration was not accounted for in these calculations. These
calculations did not account for the transportation emissions as well, which would further increase the
embodied carbon footprint of the structures and reduce the difference in their net embodied carbon impact.
A different analysis using a combination of the EC3 tool and MS-Excel was done to understand the impact
of carbon sequestration on the carbon footprints of the structures. The inclusion of sequestered carbon
reduced the net embodied carbon impact of the composite timber structure by 108% and the all-timber
structure by 191%. Between the two structures, the net embodied carbon impact reduced by 800% in the
all-timber structure when carbon sequestered in wood was accounted for. This shows that with the correct
forestry practices, timber can be used for construction to significantly reduce the carbon footprint of the
building. Timber, as compared to a concrete structure, would still have a lower embodied carbon impact
even if sequestered carbon is not considered and, therefore, its use must be encouraged to reduce the impact
of the built environment on the natural environment.

As discussed in Section 5.1, one of the limitations of using the EC3 tool for embodied carbon analysis is
its cradle-to-gate system boundary that excludes the emissions associated with transporting the materials
from the manufacturing unit to the construction. The inclusion of these emissions should be considered,
especially for timber products, as timber products are not manufactured globally yet. For this reason, a
location specific case study was selected. The net embodied carbon footprint of the existing concrete
structure of the Kanchanjunga Apartments was compared with that of a proposed CLT structure.
Information about the location of the building and manufacturing units was available for this case study.
The building was located in Mumbai, India, the concrete, rebar and steel were locally sourced whereas CLT
was transported from Japan. A comparative analysis between the structures showed that transporting the
timber from Japan, over 9000 km, increased the net embodied carbon footprint of the CLT structure by
36%. However, despite the increase in the net embodied carbon impact of the timber, the CLT structure
had a lower embodied carbon footprint by 13% than the existing concrete structure. Furthermore, the carbon
sequestered in wood was also accounted for as Japan ensures sustainable forestry practices. When the
92

carbon sequestered was accounted for, the overall impact of the CLT structure reduced by 124% as
compared to that of the concrete structure. The building had a net negative embodied carbon footprint,
which meant that the building removed more carbon from the environment than released into it. This
highlights the importance of considering where the wood is sourced from and where the timber products
are manufactured.

5.3 Future work
Additional areas were identified for further research and work. These areas are summarized in the sections
below.

5.3.1 Embodied Carbon Tools and Materials Databases
The presented research focused primarily on the use of the Embodied Carbon in Construction Calculator
(EC3) for the embodied carbon calculations. A comparative study between the embodied carbon results
derived using the tools mentioned in Table 2-3 would support identification of additional tools that provide
more accurate calculations. The identification of additional tools would identify limitations and advantages
of all embodied carbon tools, which continue to emerge due to the focus on reducing material associated
emissions. The research would support the selection of the tool based on the scope of calculations and task
easier. In addition to a database of tools, further research to gather product and material specific information
about all the timber manufacturing units and their timber products would address the challenge of a limited
database in EC3. The expanded database would ideally include all timber products and their impacts to
compare and select timber products in the early stages of the design process.

5.3.2 Carbon Sequestration
The ability of wood to sequester carbon makes it a low-carbon material. To ensure that the carbon
sequestered is accounted towards the embodied carbon calculations, sustainable forestry practices and end
93

of life scenarios need to be considered. Research on how a carbon sink deficit impacts the embodied carbon
of a timber building quantitively would further explore the importance of sustainable forestry practices. An
analysis of the different end of life scenarios for timber products and their embodied carbon impacts could
be studied as well. Furthermore, a study of forests worldwide and their forestry practices could further help
in timber product selection.

5.3.3 Structural Connections
The use of mass timber increases the quantity of steel used in the structure, as steel is needed to for
connections. A study of different timber and steel connections to optimize the quantity of steel used would
identify opportunities to reduce the amount of material. An embodied carbon comparative study between
different connection systems to derive low impact connections could also help in reducing the net embodied
carbon footprint of a timber structure. In addition to this, a Revit family library for these connections could
be created. This would make it easy to model the timber structures accurately on Revit, which would ensure
more accurate material quantities and thus, more accurate embodied carbon results. Other materials that
would provide the same structural strength as steel but have a lower carbon impact could be studied for
timber connections as well.

5.3.4 Mass Timber
Mass timber products require adhesives for their structural stability. Research about the impacts of using
these adhesives on the indoor air quality could be studied. Furthermore, a separate study focusing on the
embodied carbon footprint of the adhesives could be done to identify low-carbon adhesives. Timber is still
a developing industry and timber products are not produced globally yet. As a result, to be able to build in
some places with timber would require transporting the timber from different countries. This study
considered one location specific case study to analyze the impact of transporting the timber from another
country on the net embodied carbon footprint of the building. A study that would consider transportation
94

of timber from major timber producing countries to developing countries and analyze and compare their
impacts on the net embodied carbon of the building could be done. To further understand the impact of
using mass timber products on the operational carbon of the building could also be done. This would help
in identifying strategies for optimizing the building envelope to reduce both the operational and embodied
carbon of a timber building. Studies that analyze the impact of wood on other factors like indoor air quality,
indoor environmental quality, occupant wellbeing and comfort, etc., as compared to buildings made using
conventional materials could be carried out. A study to understand the impact of exposed wood in the
interior surfaces on occupant wellbeing as compared to concealed wood could be done as well.

5.4 Summary
The high impact of the built environment makes it important to reduce the net carbon footprint of the
building. Since high-performance buildings optimize the operational carbon of the building, addressing the
embodied carbon of the building is important. The use of low-carbon footprint and carbon sequestering
materials can reduce the embodied carbon of a building, which has led to a rise in the use of timber in the
construction industry. The low net embodied carbon of the material along with its structural properties
makes it a very good material for construction. The availability of engineered timber has made the
construction of tall timber towers possible.

The environmental impact of the built environment can be assessed using LCA tools. Conventional LCA
methods calculate the impact of the building through all its stages- from resource extraction to its disposal.
This method is an extensive and complicated task, with several disadvantages. The Embodied Carbon in
Construction Calculator (EC3) tool addresses the product stage, the highest contributor to the net embodied
carbon, of the LCA and uses product specific EPDs to analyze the embodied carbon impact of materials
used.

The embodied carbon analysis was done using two case studies, the composite-timber and all-timber
95

structures of the Dewitt-Chestnut Apartments and the concrete and CLT structures of the Kanchanjunga
Apartments. An analysis between the published and EC3 embodied carbon values showed that EC3
enhanced the accuracy of the calculations and provided precise values as it used manufacturer values rather
than industry averages. A comparative analysis between the composite-timber and all-timber structures of
the Dewitt-Chestnut Apartments showed that the all-timber structure performed better than the composite-
timber structure. The difference was not significant, however, the inclusion of carbon sequestration resulted
in a net negative embodied carbon for both the structures, causing a reduction by 800% in the total embodied
carbon footprint of the all-timber structure as compared to the composite-timber structure. A location-
specific analysis was also done to address the impact of transporting the timber long distances, as timber is
not available globally. The Kanchanjunga Apartments in Mumbai, which was redesigned using CLT as part
of a conference, was used as the case study for this study. The results of the analysis showed that even
though the CLT was transported from Japan to Mumbai, the CLT structure performed better than the
existing concrete structure. The inclusion of carbon sequestration resulted in a net negative embodied
carbon impact of the building, and a 124% reduction as compared to the concrete structure. The analyses
highlighted the influence of the transportation and carbon sequestration on the net embodied carbon results,
and the importance of sustainable forestry practices.

Several additional areas of research were identified in the process. The exploration of different embodied
carbon tools and development of a timber database that includes all timber products could be done. Research
on the quantitative impact of carbon sink deficits on the net embodied carbon footprint of using timber
could explore the importance of sustainable forestry practices. The use of mass timber increases the quantity
of steel used in the structure, as steel is needed to provide tensile strength to the timber products and for
connections. A study of different timber and steel connections to optimize the quantity of steel used could
be done. Revit families of steel connections could make it easier to model steel accurately, which could
increase the accuracy of material quantities. Lastly, research on reducing the embodied carbon impacts of
adhesives could also be done to further optimize the embodied carbon footprint.
96

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Abstract (if available)

Abstract The impacts from the built environment are significant and therefore it is important to reduce the carbon footprint of buildings. Technological advancements have made it possible to reduce the operational carbon of the building, making it important to address the embodied carbon footprint of the building. The use of low-carbon footprint and carbon sequestering materials can reduce the embodied carbon of a building, which has led to a rise in the use of low carbon materials, such as timber, in the construction industry. The low net embodied carbon of the material along with its structural properties makes it a very good material for construction. The assessment of embodied carbon is a time consuming and complex task. This has resulted in the absence of a particular method of calculation. A cradle-to-gate assessment of the embodied carbon of a tall timber tower, using the Embodied Carbon in Construction Calculator (EC3) tool, was used as a case study to understand the impact of the use of product specific Environmental Product Declarations on embodied carbon calculations. The embodied carbon of different timber structural systems was compared. In addition, the impact of transportation emissions on the net embodied carbon of buildings was also studied by using a location specific case study. ❧ The analyses showed that the EC3 tool enhanced the accuracy of the embodied carbon calculations by providing precise manufacturer values, instead of industry values. The results also indicated that the method produced a conservative analysis as it does not account for carbon sequestration by wood. The study also showed that timber as a material for construction reduced the net embodied carbon of the building, even if the carbon sequestered by wood is not accounted for and even if the timber product is not locally produced. Sustainable forestry practices ensure the inclusion of the carbon sequestered by wood, which substantially reduces the net embodied carbon, often resulting in a net negative embodied carbon. The analyses showed the impact of carbon sequestration on the net embodied carbon footprint of the building, making it important to sustainably manage forests. The forest source of the wood, the location of the manufacturing unit and the location of the construction site are also important considerations for accurate embodied carbon calculations.

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University of Southern California Dissertations and Theses

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Asset Metadata

Creator Vora, Rushita (author)

Core Title Embodied carbon of wood construction: early assessment for design evaluation

School School of Architecture

Degree Master of Building Science

Degree Program Building Science

Publication Date 04/14/2021

Defense Date 03/15/2021

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

Tag Building Information Modelling,carbon sequestration,embodied carbon,engineered timber,environmental product declarations,OAI-PMH Harvest,Timber

Language English

Contributor Electronically uploaded by the author (provenance)

Advisor Sharma, Bhavna (committee chair), Kensek, Karen (committee member), Schiler, Marc (committee member)

Creator Email rjvora@usc.edu,rushitav@gmail.com

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c89-442625

Unique identifier UC11668759

Identifier etd-VoraRushit-9458.pdf (filename),usctheses-c89-442625 (legacy record id)

Legacy Identifier etd-VoraRushit-9458.pdf

Dmrecord 442625

Document Type Thesis

Rights Vora, Rushita

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