Embodied Carbon

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EMBODIED CARBON Exploring Global Warming Potential Using Life Cycle Assessments

Soto Building

EMBODIED CARBON Exploring Global Warming Potential Using Life Cycle Assessments Author: Kate Sector Advisor: Ryan Yaden


What is the carbon impact of materials being used in LF’s projects and how can we quantify and reduce those impacts? ABSTRACT The built environment is a substantial contributor to Global Warming Potential (GWP) through both the energy and fossil fuels required to operate buildings as well as the embodied energy and carbon of all the materials needed to construct it. Our research will cover an introduction to embodied carbon and life cycle assessment (LCA), and will investigate workflow methods for conducting LCAs with tools such as Tally. We will then present multiple case studies that show how to perform LCAs at key design stages to quantify the impact of material selection. Finally, we will show how to use this data to make the critical design choices that will reduce a building’s carbon footprint and subsequent contribution to climate change as well as suggest future research and exploration.

KEYWORDS Embodied Carbon, Life Cycle Assessment, Tally, Mass Timber, Steel, Concrete, Structure, Wall Assembly.

INTRODUCTION The built environment is a substantial contributor to a variety of negative environmental and human health impacts. The most concerning of these is global warming potential (GWP) (NOAA, January 2019). Global warming potential is measured in kgCO2eq and describes the potential changes in surface temperatures caused by Green House Gas (GHG) emissions such as carbon dioxide gas. ‘CO2 emissions’ or ‘Carbon’ is often used shorthand to refer to GWP. “Globally, the building and construction sectors account for nearly 40% of global energy-related carbon dioxide emissions in constructing and operating buildings“ (Simonen, Huang, X. Rodriguez, & Todar, 2019). Buildings contribute to GWP in two ways. The first is through operational energy which is the energy used to operate our buildings. Historically, the energy produced to operate buildings has come from non-renewable sources such as fossil fuels which directly contribute to global warming potential through operational carbon. Global warming potential from operational energy can be reduced by first designing a building to perform more efficiently and switching to renewable sources of energy such as solar and wind-generated power, which don’t contribute to GWP during a building’s operation. The second way a building contributes to GWP is through embodied energy, the energy consumed by building materials during a building’s full life cycle - from extraction to end of life and disposal. Embodied carbon refers to the GWP produced from materials and energy used in the construction, maintenance, and disposal of buildings” (Simonen, Huang, X. Rodriguez, & Todar, 2019).


DEFINITIONS AND ABBREVIATIONS Global Warming Potential (GWP): “Describes potential changes in local, regional, or global surface temperatures caused by an increased concentration of GHGs in the atmosphere, which traps heat from solar radiation through the ‘greenhouse effect’“ (Simonen, Huang, X. Rodriguez, & Todar, Life Cycle Assessment of Buildings Version 1.1, 2019). Greenhouse Gas (GHG) Emissions: Gases that trap heat in the atmosphere and contribute to the disruption of the global climate. (United States Environmental Protection Agency (EPA), 2021) (Simonen, Huang, X. Rodriguez, & Todar, Life Cycle Assessment of Buildings Version 1.1, 2019). Carbon Dioxide (CO2): “The primary greenhouse gas emitted through human activities. Carbon dioxide enters the atmosphere through burning fossil fuels (coal, natural gas, and oil), solid waste, trees and other biological materials, and also as a result of certain chemical reactions (e.g., manufacture of cement). Carbon dioxide is removed from the atmosphere (or “sequestered”) when it is absorbed by plants as part of the biological carbon cycle” (United States Environmental Protection Agency (EPA), 2021). Carbon Dioxide Equivalent (CO2e or CO2eq): “A metric measure used to compare the emissions from various greenhouse gases on the basis of their global-warming potential (GWP), by converting amounts of other gases to the equivalent amount of carbon dioxide with the same global warming potential” (Eurostat , 2001).

Unlike operational carbon that builds up slowly over a building’s life time, embodied carbon starts being emitted as soon as a material is extracted and until it is implemented on the site. Because of this, addressing embodied carbon is becoming more urgent because the carbon has been emitted the day the building is completed. There are many solutions to minimizing embodied carbon such as reusing buildings and salvaging materials, reducing concrete and steel, using bio-based and locally sourced materials. This journal will discuss in detail many of these paths to zero. Ideally, architects should strive for zero carbon in terms of both operational and embodied carbon (King, 2018). The International Living Future Institute (ILFI) perhaps describes this effort best through their Zero Carbon Certification standard, where: “one hundred percent of the operational energy use associated with the project must be offset by new on- or off-site renewable energy. And one hundred percent of

DEFINITIONS AND ABBREVIATIONS Operational Energy: “The energy that is used during the occupancy stage of a building’s life cycle for space and water heating, space cooling, lighting, running the equipment and appliances, etc.” (ScienceDirect, 2021) Operating Carbon: “Refers to the GWP attributed to operation and use of the building” (Simonen, Huang, X. Rodriguez, & Todar, Life Cycle Assessment of Buildings Version 1.1, 2019). Embodied Carbon: “Refers to the GWP attributed to materials and energy used in the construction and maintenance of buildings” (Simonen, Huang, X. Rodriguez, & Todar, Life Cycle Assessment of Buildings Version 1.1, 2019).


the embodied carbon emissions impacts associated with the construction and materials of the project must be disclosed and offset” (International Living Future Institute, 2021). Addressing both operational and embodied carbon is critical if designers are to meaningfully slow human-influenced climate change. Architects, aided by increasingly strict energy codes and greater client and firm commitments to sustainability, can decrease buildings’ operational impacts by reducing energy use intensity (EUI) and integrating more renewable energy sources into projects. However, the embodied carbon of materials has not seen the same degree of improvement yet. As buildings become more efficient and operational energy decreases as a result, addressing embodied carbon becomes an equally pressing issue for the architecture industry. For example, if a building has zero operational carbon due to a low


EUI supplemented with renewables, the embodied material impact now makes up 100% of that building’s GWP. This is critical because, according to Architecture2030, “between now and 2060 the world’s population will be doubling the amount of building floor space, equivalent to building an entire New York City every month for 40 years” (Architecture2030, 2021). Building industry professions have a tremendous opportunity to reduce buildings’ impact on GWP through investigated design decisions that reduce embodied carbon. This leads to our main question:

How do designers quantify embodied carbon in a meaningful way to set benchmarks and reduce a building’s impact?

LIFE CYCLE ANALYSIS BACKGROUND To quantify and track the embodied emissions of buildings, designers can examine building materials and assemblies (e.g. walls, floors, roofs, etc.) with Life Cycle Assessments (LCA), a process that has been outlined in the Life Cycle Assessment of Buildings: A Practice Guide, which is summarized in this section (Simonen, Huang, X. Rodriguez, & Todar, 2019). A Life Cycle Assessment (LCA) is a calculation method for determining the cradle to grave (extraction to

DEFINITIONS AND ABBREVIATIONS Life Cycle Assessment (LCA): “A systematic process for identifying, quantifying, and assessing environmental impacts throughout the life cycle of a product, process, or activity. It considers energy and material uses and releases to the

disposal) related to environmental impacts, such as global warming potential of a product or material. Based on the results of the LCA, designers can select materials that acquire the smallest carbon penalty. While LCAs measure emission impact categories such as Ozone Depletion Potential (ODP), Ozone Creation Potential (POCP), Non-Renewable Primary Energy, acidification potential, and eutrophication potential, the focus of this paper is on Global Warming Potential.

transparent and comparable information about the life cycle environmental impact of products. As a voluntary declaration of the life cycle environmental impact, an EPD for a product does not imply that the declared product is environmentally superior to alternatives” (The International EPD® System, 2021).

environment from ‘cradle to grave,’ (i.e., from raw material extraction through manufacturing, transportation, use, and

Carbon Sequestration: “The act of extracting carbon dioxide

disposal)” (Elcock, 2007).

from the atmosphere and storing it in a long-term form is known as carbon sequestration” (Simonen, Huang, X. Rodriguez, &

Whole Building LCA: “Whole building LCA (WBLCA) is a term

Todar, Life Cycle Assessment of Buildings Version 1.1, 2019).

that is often used to refer to LCAs of buildings. However, not all ‘whole’ building LCAs truly encompass the ‘whole building.’

Biogenic Carbon: “Biogenic carbon refers to carbon that is

Often, these assessments only include certain components,

‘produced in natural processes by living organisms but not

such as structure and enclosure, and exclude components such

fossilized or derived from fossil resources.’ In the building

as MEP, site work, or interiors” (Simonen, Huang, X. Rodriguez,

industry, this most commonly occurs in wood products. Other

& Todar, Life Cycle Assessment of Buildings Version 1.1, 2019).

biogenic construction materials may include bamboo, straw, and cork. Sequestered carbon can be reported as a negative

Environmental Product Declaration (EPD): “An independently verified






carbon ‘emission’” (Simonen, Huang, X. Rodriguez, & Todar, Life Cycle Assessment of Buildings Version 1.1, 2019).


There are 4 key stages of a material’s life: 1: Production and construction: Includes the extraction of raw materials, transportation to the manufacturer, product manufacturing and production. This also includes transportation to the construction site and construction installation. Environmental Product Declarations (EPDs), available for some products, only account for this stage.


2: Use: Includes the operational energy of the building and maintenance of building materials. Not all LCAs account for operational energy, and this is typically part of a separate optional calculation. 3: End-Of-Life: Includes demolition and disposal. 4: Externalized impacts beyond system boundary: Includes miscellaneous effects of re-using, recycling, and/or recovering materials.

By analyzing these various stages through LCA tools, designers can estimate the various environmental impacts of the materials they choose. LCAs can help designers and building owners make informed choices regarding the environmental impact, cost, and resilience of their building materials through benchmarking and comparison. In addition, LCAs are used to achieve various certifications

including LEED V4 and the Living Building Challenge. LCAs can be performed at various stages in the design from concept to post occupancy evaluation, each offering their own individual value to help reduce embodied impact. For a full reference guide, see the CLF’s: “Road Map to Reducing Building Life Cycle Impacts” (Carbon Leadership Forum, 2020).


METHODS Each case study in this investigation follows the methodology set up by the Carbon Leadership Forum’s “Life Cycle Assessment of Buildings: A Practice Guide” as well as the Tally LCA Guide “Performing a Life Cycle Assessment within a Revit Model” (Bates & Welch, 2014) (Simonen, Huang, X. Rodriguez, & Todar, 2019). This section intends to summarize and pull out the key elements that are relevant to the subsequent case studies in this investigation. The method for analyzing a building’s embodied carbon according to

1. Define your Goal and Scope Define Your Goal/Scope: What are we looking at, and why? It is critical to clearly define what the scope and goals are of the project in terms of its ‘functional and performance equivalence’ to ensure appropriate comparisons are being made between projects (King, 2018). A great template for defining the scope and goals is the “Taxonomy for Whole Building LCA” by the CLF (The Carbon Leadership Forum, 2020). Some of the key things you will want to define before starting an LCA: Goal: Why are you conducting an LCA? Some reasons for conducting an LCA include helping with material decision making and to compare design options, finding the “hot spot” or main carbon-producing material in a building, running a whole building LCA for certification purposes, etc. Functional Equivalence Scope: What is the function and performance of the building? The functional description of the building allows for an “apples-to-apples” comparison of your goals and scope to other projects.


CLF is divided into five steps: (1) Define your goal and scope, (2) complete a life cycle inventory, (3) perform a life cycle assessment, (4) interpret and reiterate results if needed, and then (5) report the results. The case studies that follow show how this process can be applied at a variety of stages in design to achieve a range of goals anywhere from a whole building LCA for a building certification to simply comparing material options to help narrow down a façade material, for example. Here is a summarized breakdown of each step:

This includes project information such as building type, climate zone, use patterns, and building characteristics such as height and energy performance.

Boundary is typically A1-A4, B2-B5, C2-C4, and Module D. Reference the CLF guide for an explanation of these designations.

Reference Study Period: What is the building lifespan and service life of the materials being used? Optional activities related to materials or operational energy such as transportation, construction, energy consumption, water consumption, and water treatment can be included as well as at the end of the study. In addition, replacement and end of life use of the materials should be considered. A material with low embodied carbon that needs to be replaced every five years may not be a low-carbon option over the life of the building.

System Boundary | Environmental Impact Categories: What impact(s) will be studied? LEED requires all of the following: Global Warming Potential (GWP), Ozone Depletion Potential (ODP), Smog Formation Potential, Primary Energy Demand, Acidification Potential, and Eutrophication Potential, etc. But you can choose to only look at specific categories. The subsequent studies focus on the GWP category.

System Boundary | Physical Scope: What building elements will be studied? Will you be performing a whole building LCA or a study between individual materials? Identify a very specific goal. System Boundary | Life Cycle Assessment Stages: What life cycle stages will be studied? The default System

System Boundary | With Biogenic Carbon Credit vs Without Biogenic Carbon Credit: Will the sequestration ability of certain products be included? Biogenic carbon is described as the carbon that is “produced in natural processes by living organisms but not fossilized or derived from fossil resources” (ISO, 2013). You can choose to include Biogenic or not, but it is important to indicate the choice.

2. Collect Material Inventory

3. Perform Impact Assessment

To complete an LCA, designers need to collect a bill of materials and activities. Not only should designers have a list of materials featuring quantity, life span, and life cycle stage, but they should also have activities related to those materials such as transportation and construction, as well as what happens to the material at the end of its life. LCA tools require different methods of collecting inventory. For example, with tools like Athena, you can manually input a bill of materials. However, other tools like Tally rely on BIM and the materials modeled within the software. Both have an embedded library of LCA material data.

Pick a software! There are many tools available on the market today that can measure carbon impact such as Tally, Athena, One Click LCA, and more. Tally LCA software, which is compatible with Revit, was used in this study to quantify the embodied carbon at key design stages to understand impacts of material selection decisions. Each tool follows a similar method of first collecting quantities of materials and then multiplying by the estimated environmental impact of each material to get the total building impact. LCA tools use a variety

of sources for their data. Most Life cycle inventory (LCI) databases are created and managed by governmental, non-governmental, and private organizations. For example, Tally gets its data from the US Life Cycle Inventory Database, GaBi, and EPD Standard (Tally, 2021). For a guide on using Tally to perform LCAs see: “Performing a Life Cycle Assessment Within a Revit Model” (Bates & Welch, 2014).

5. Report Results

4. Interpret Results LCAs are a very iterative process and often require re-running and analyzing the results. The process will be different depending on the intended goal and scope of each project, but for every analysis it is critical to check for errors. The Carbon Leadership Forum recommends doing this in several ways: 1. Compare your LCA to similar LCA studies. However, be very careful when comparing to other LCAs because the inputs and scope can drastically differentiate every LCA. 2. Compare to a baseline building or benchmark material. If you are doing a whole building analysis or comparing to data outside your tool, you will need to create or select a

reference benchmark. Similarly, if you are analyzing design options for a particular element within a project, it helps to designate one of the material options as your baseline for comparison with the others. 3. Evaluate material impacts and quantities. Focus on the big takeaways and percent reduction between materials for a whole building study, rather than fine details. There is often a large margin of error within individual material data (King, 2018). Remember that these are newly accessible tools/data and designers need to be transparent that this is an ever-evolving field. There is a high level of uncertainty in results due to data used, the tool, the inputs, etc.

In Tally, there are two main ways to view your results: one in PDF and one in excel. The PDF provides you a great overview with charts and graphics automatically produced for all impact categories. The excel sheet is a great way to make material comparisons or isolate certain impact categories you want to study. For example, given these study scopes only look at GWP, all data is isolated to only include GWP. There are many certifications such as LEED and Living Building Challenge that use LCA towards building certification credits. They each have their own guidelines for reporting. Regardless of pursuing a certification, please be transparent and share your results with others to help spread knowledge on LCAs!


1221 Broadway Lofts

Magdalena Hotel

University of Denver Career Achievement Center


CASE STUDIES OVERVIEW Each of the following studies investigates one of many paths that can bring a building’s carbon footprint toward zero. Each investigation is made possible by LCA tools. These paths to zero include but are not limited to the following best practices: reuse of buildings or salvaging materials, optimization of materials in the structure to reduce concrete and steel, the incorporation of biomaterials to help

sequester carbon, using low carbon alternative products, and sourcing local materials to minimize transportation impacts. Each option is accomplished through exploring design options and/or completing a whole building life cycle assessment, and each will include a project overview, scope and goals, initial research on materials, results of the study, and lessons learned.



1221 Broadway Lofts


1221 Broadway Lofts

Understanding the Impacts of Building Reuse. Scope:

Location: Typology: SF: LCA Type: Life Span: Life Cycle: LCA Tool:

San Antonio, Texas Apartment Complex 410,000 Post Occupancy Structure focusing on Concrete and CMU 60 years A1 - D3 Tally

Question: How much carbon was avoided by reusing the existing concrete structure? Carbon Challenge: Concrete has played a critical role in architecture throughout history, allowing architecture to take new forms and explore ideas designers had only dreamed of. It is also a highly durable material that provides longevity and resilience. However, cement has a high global warming potential impact, which is prompting the architecture industry to rethink the use of concrete (Babor, 2009). Although designers should critically challenge the role concrete plays in the built environment, we also want to acknowledge its benefits and reuse what has already been created where possible. Carbon Strategy: Reuse. One of the most important strategies designers can employ to reduce embodied carbon is to reuse existing materials. One example of the reuse of concrete is the revitalization of 1221 Broadway Lofts. Lake|Flato Architects, in collaboration with LPA Design

Studios, transformed 1221 Broadway into a unique oasis with an urbane street presence. The old apartments were re-skinned, and their windows enlarged to allow in more natural light. The ground floor exterior now accommodates office and retail space on Broadway Street, while five interior courtyards link urban living with nature, providing forums for outdoor activity. (Lake|Flato Architects, 2020). In this study we investigate the structural concrete in isolation to quantify how much carbon was saved by reusing an existing structure. In this study we investigate how much kgco2eq was avoided by reusing the existing structure, instead of tearing it down and building a similar new concrete structure in its place. To do this, we quantified the kgco2eq that was emitted by the original structural concrete in isolation.


Results: Through the analysis, it was discovered that the embodied carbon of the original concrete and concrete block structure was approximately 12 million kgco2eq. This number is roughly equal to the greenhouse gas emitted from 9,500 passenger vehicles driven for 1 year. Sequestering this amount of carbon would require around 950 acres of forest grown for 60 years. Even if a replacement structure were to have contained less embodied carbon than the demolished one, reusing the structure saved a significant amount of embodied carbon.


This led to another question: At what point in the carbon reduction decision does it make sense to tear down an existing building and replace it with a more energy-efficient structure? Constructing a new building likely carries significant embodied carbon costs. However, depending on the energy use intensity (EUI) and the lifespan of the new building, that cost may be offset by the lower operational carbon made possible by a more energy efficient design. We looked at a simplified theoretical scenario to understand the long-


term trade-off of carbon. The new building (blue) when built produced 12 million kgco2eq due to embodied carbon of the materials whereas the retrofitted building (orange) reuses the existing structure so in theory adds zero embodied carbon. To compare these two over time, two different EUI s are used: A code compliant EUI of 50 kBtu/sf/yr and an alternatively low EUI of 10 kBtu/sf/yr. The varying EUIs over time start to highlight how important both operational and embodied energy are when it comes to achieving zero embodied carbon. For example, you can have a low embodied carbon building through materials reuse, but if the building does not have a low operational energy use as well, by the end of its lifespan it

will have produced more carbon than the new building with a low EUI. The key takeaway is that a retrofit is only as effective in reducing carbon over time if operational emissions can also be reduced. Future Investigations: This study only investigated the carbon impact of reusing a structure. In the future it would be beneficial to better understand the embodied carbon impact of full renovations, including how future interior renovations and maintenance of a building impact embodied carbon over time. What role do these play in the carbon trade-off of retrofits vs. new buildings?


Magdalena Hotel

18 The Lodge at Gulf State Park

University of Pennsylvania - Data Science Building

CASE STUDY 2 | MASS TIMBER STRUCTURES Comparing Concrete and Steel to Mass Timber Scope: Gulf State Lodge

Arizona State University

Penn Data Science


Gulf Shores, AL

Phoenix, AZ

Philadelphia, PA

Austin, TX



Higher Ed

Data Science







Structure - See appendix for details

Life Span

60 Year

Life Cycle

A1 - D3 Tally

LCA Tool

Hotel Magdalena

(Babor, 2009) (Hasanbeigi, 2019). The supply of cement and its aggregates is a finite resource, and in recent years there has been a shortage of Portland cement, gravel, and sand (King, 2018). Currently, the most effective approach to reduce the GWP of concrete is to use less Portland cement and use supplementary cementitious materials such as fly ash or slag (Architecture 2030, 2021). Other strategies include specifying strength only when you need it and to optimize the reduction of materials. New technologies like Carbon Cure and other forms of binders inject carbon into the concrete mixture to stabilize it. Bruce King - New Carbon Architecture

Question: What parts of a building and what materials produce the most embodied carbon? How do we reduce that impact? The Challenge: Concrete and Steel A building’s structure is responsible for a significant portion of a building’s total embodied carbon impact, followed by envelope and interior finishes (King, 2018). Concrete and steel are core materials used in construction today and have relatively high embodied impacts due to their intense material process. According to the 2018 Global ABC Report, 22.7% of global carbon emissions are from concrete, steel, and aluminum alone (International Energy Agency, 2018). Concrete has high GWP primarily due to cement production, which accounts for 6% of anthropogenic global emissions

Steel typically has a high GWP due to the high heat intensity needed to produce it, but its impact varies due to the range of recycled content utilized and the region it is produced in (Architecture 2030, 2020). The type of energy (renewable or fossil fuel) used to produce the material also greatly influences the GWP. If there are renewables associated with the manufacturing, this can help lower the overall embodied carbon impact.


Carbon Strategy: Mass Timber One of the many benefits of mass timber products such as glulam, cross laminated timber (CLT), and dowel laminated timber (DLT) is the significantly lower GWP range due to the material’s ability to sequester carbon throughout its life cycle (King, 2018). The ability to sequester carbon during growth, also known as biogenic carbon, allows many biobased products to serve as a carbon sequestering alternative to concrete and steel. Biogenic carbon is described as the carbon that is “produced in natural processes by living organisms but not fossilized or derived from fossil resources” (ISO, 2013). However, reduced carbon impact through sequestration is not guaranteed when using biomaterials. There is a high level of uncertainty in the industry when it comes to calculating the actual impact. Variations in forestry practices and management, distances between extraction, manufacturing, and project site, and manufacturing conditions all impact the overall carbon sequestration, and therefore GWP of wood. For example, one study observed that Forest Stewardship Council (FSC) wood had consistently higher average carbon storage than certifications such as SFI due to FSC’s sustainable practices and longer rotation cycles (David D. Diaz 1, 2018). Another study produced by Arup focused on worst case to best case scenario wood products including transportation and harvesting practices. The study found that a worst case timber product could produce almost as much GWP as concrete (King, 2018). Given the margin of error within wood products, designers looking to minimize carbon impact must be careful where they source their wood and which timber harvesters and fabricators they support.


When performing an LCA that includes bioproducts like wood, designers have the choice of whether to accept a credit for biogenic carbon or not. In LCA software like Tally, if you select biogenic carbon, the sequestration potential is considered and reported as a negative carbon emission. Programs such as LEED recommend including biogenic carbon in LCA calculations to supply credit for using a bio product. The CLF suggests the following method if you choose to report biogenic carbon: “Report the sequestration credit as a separate negative value (not added to the positive emissions values). If your biogenic material is wood, report the status of forest certification.” (Simonen, Huang, X. Rodriguez, & Todar, Life Cycle Assessment of Buildings Version 1.1, June 2019). Regardless of the option you choose, you should clearly indicate whether you have taken credit for biogenic carbon.

Results: In this study we are choosing to report both with and without the biogenic credit to compare both options and be transparent regarding the potential sequestration ability of wood. Four designs were studied that each compare a

structural baseline model of concrete and steel to a mass timber option. Each building varies slightly in its concrete, steel, and mass timber ratios, which are described in the table below:


Results indicate that when including biogenic carbon, switching to a mass timber structural system can provide a tremendous carbon reduction, ranging from 38% to 58% depending on how much mass timber is replacing concrete or steel. When biogenic is not included, the carbon reduction is significantly less, ranging from a 7 to 17% reduction. Although mass timber is a way to reduce GWP, there is a clear discrepancy between including and not including biogenic carbon. It’s important that when choosing a structural system,


designers go the extra mile to ensure the wood being specified will have a lower GWP. Given that concrete and steel remain critical building elements in the industry today, designers should find ways to minimize the carbon impacts of concrete and steel, whether they are a primary or secondary structural material. This can be done by referencing the carbon emissions listed in Environmental Product Declarations (EPDs) and by including specific requirements in material specifications. EC3 offers an online tool for finding low embodied carbon EPDs.

Future Investigations: After researching mass timber’s effect on embodied carbon, many questions remain. A major concern regarding timber and the benefit of biogenic carbon is what happens to that sequestered carbon at the end of the product’s life cycle. If a bioproduct is sent to the landfill or incinerated, for example, that sequestered carbon is then released into the atmosphere, counteracting its upfront benefits (King,

2018). In addition, other problematic environmental impacts of logging, such as acidification and eutrophication, remain. Future research should investigate additional ways designers may ensure minimal environmental impact through their specification of mass timber products. These strategies include addressing end of life uses and additional impacts like acidification.

The Marine Education Center at The Gulf Coast Research Laboratory (GCRL)



CASE STUDY 3 | WALL ASSEMBLIES Understanding the impact of common Lake|Flato wall materials. Scope:

Location: Typology: SF: LCA Type: Life Span: Life Cycle: LCA Tool:

n/a Residential and small commercial n/a - 10x10ft wall samples Wall assemblies Varies by material (mostly 60 year) A1 - D3 Tally

Question: What is the environmental impact of materials being used in LF’s projects? How can our projects be carbon neutral and begin to look at the other environmental impacts of our material choices?

This study ran an analysis on multiple materials used in a common non-structural wall assembly including siding, rigid insulation, framing and cavity insulation, and interior finishes. The life span varies per material but has been standardized to the best of our ability. Each material quantity assumes a 10 ft x10 ft wall assembly, so the GWP for each material represents roughly 100 square feet of material. The following will identify the best and worst case embodied carbon options of those we examined in each category. Thickness and weight for each material were normalized according to typical construction detailing.


Cavity Insulation


Rigid Insulation


Carbon Challenge: Embodied carbon is found in all parts of a building, not just in its structure. When structural elements and optimization of material reduction are out of a designer’s control, there is still room to reduce embodied carbon in other parts of the building, such as facades and wall assemblies more generally. Methodology: The purpose of this study is to identify where Lake|Flato could make smarter embodied carbon choices within wall assemblies. The following results will indicate the top solutions for low embodied carbon alternatives to common materials used in wall assemblies. They are presented from interior to exterior and include insulation, framing, and more.


Siding: Given Lake|Flato’s wide variety of projects, designers studied multiple siding options while considering optimization and reuse of certain materials. According to the 10x10 wall samples analyzed in Tally, the lowest GWP materials were recycled copper, zinc, ¾” softwood siding (with the potential to be carbon negative), and ¾” thin brick. The higher embodied carbon materials were a 3 5/8” granite veneer, ¾” GFRC, 3 5/8” limestone, and 4” precast concrete. A key finding from this study was that recycled materials help lower embodied carbon as well as optimization of


material reduction. For example, designers compared a thin veneer brick to a standard brick, and a limestone veneer to a granite veneer. In each case, the thinner version reduced embodied carbon substantially. Future Questions: 1. What other biomaterial or carbon sequestering sidings are available? 2. How does material resiliency and lifespan play a role in the embodied carbon of material maintenance?

Rigid and Cavity Insulation: Both rigid and cavity insulation were investigated and equalized by their R-value performance. The rigid insulations were set to an R-3.8 and the cavity insulations set to an R-13. For rigid insulations, XPS has the highest GWP out of the four studied insulations. XPS is a petroleum-based product that requires significant energy to manufacture, resulting in a high embodied carbon footprint. For cavity insulations studied, closed cell polyurethane foam that is spray-applied had the highest GWP out of the group. The leading contributor to a high global warming potential is the spray foam insulation application. Advice from Carbon Smart Materials Palette suggests specifying blown-in over rigid or spray foam whenever possible (AIA2030 Challenge, 2021). The fiberglass and cellulose insulation had the lowest embodied carbon by a significant amount. Cellulose even

has the potential to achieve a negative carbon value given its biogenic sequestration potential highlighted in green on the following graphs. Future Questions: 1. What causes the high GWP of each material? Are there solutions to help reduce the embodied carbon within commonly used materials? 2. How well do lower embodied carbon and bio-based sequestering insulations compare to our common materials such as cork and strawbale? 3. How does the application of insulation impact the embodied carbon? 4. How does the longevity and replacement of insulation over time impact embodied carbon?


Framing: This study compares 2x4 and 2x6 wood framing to 3-5/8” and 6” metal studs. To better understand how durability and longevity of a material plays a role in embodied carbon, this study was set to a 100-year life span for both metal and wood framing. Metal framing may be more durable than wood framing, requiring less upkeep and lasting longer, therefore potentially lowering its embodied carbon. The results of this study were fascinating due to the potential sequestration of wood framing. If you do not include biogenic carbon (orange), the 3 5/8” metal framing has the lowest GWP. However, when biogenic is included, the 2x6 wood framing option yields a negative GWP because of the wood’s potential ability to


sequester carbon. This study becomes even more complex when designers consider the durability and longevity of each material. The main takeaway from this study is that more research needs to be done and it is unclear which material yields the lower embodied carbon. It will depend greatly on the life span of the building, where each material is sourced, and more. Future Question: 1. What is the embodied carbon of framing and is there a lower carbon material solution appropriate for various buildings?

Interiors: This interiors study looked at four common materials, including: ceramic tile, gypsum board, interior grade plywood, and wood planks. Finishes of each were not included. The assessment was run two ways - taking credit for biogenic carbon and not taking credit. When the credit was not accepted, a thinner 5/8” gypsum wall board was the lower embodied carbon solution and 2” wood planks were the highest. However, if biogenic credit was accepted, the carbon sequestering properties of the wood planks caused them to be the lowest embodied carbon option, and the 5/8” gypsum wall board was the highest. One takeaway from this study was the consideration of manufacturing conditions, specifically in gypsum wall board specification. According to the Carbon Smart Materials Palette, gypsum wall board is a fairly energy intensive product to make due to the heat and water needed to make the mix. Specifying light weight or thinner gypsum wall board can help reduce waste and its carbon footprint

(2030Challenge, 2021). Another key topic to consider with interiors is renovation and durability of materials. Interiors are often retrofitted and changed as the building program or tenants change. The carbon impacts of these small changes add up over time. One study by LMN Architects analyzed the impact of cyclical interior renovations of an office. LMN’s study revealed that the cumulative embodied-carbon footprint of the remodeling projects was greater than that of the structure, the original envelope, and a new curtain wall combined (Gonchar, 2020). Future Questions: 1. What is the interior maintenance and turnover rate of our projects? 2. How does this influence embodied carbon and where can improvements be made?


Full Wall Assembly Conclusion: This study helps us make informed decisions about our wall assemblies and choose durable, long-lasting assemblies that not only cut down on operational energy through high performance but also reduce embodied carbon through informed material selection. A final quick study looked at two wall assemblies: a theoretical worst case and best case scenario. The worst case was a granite veneer, XPS continuous insulation, 6” metal stud with closed cell spray and a standard 5/8” gypsum wall board. The best case was wood siding, rigid mineral wool continuous insulation, 6” wood stud with cellulose cavity insulation and a thin gypsum wall board. These two assemblies yielded a major embodied carbon difference even with biogenic credit not taken. With the biogenic carbon not included, there was an 86% reduction from worst case to best. When biogenic credit was included, the best case scenario yielded a 103% reduction in embodied carbon, making it potentially carbon negative. These small material choices that designers make every day when doing design options for wall assemblies make a tremendous difference when considering the scale of a full building. Many further research questions remain from this early study including: Future Research Questions: 1. What is the embodied carbon of rammed earth? 2. What is the embodied carbon impact of a typical L|F residential home or eco-conservation project? 3. What is the triple bottom line for all these materials? Some are worse or better compared to others. How can we tie-in performance, cost, life span, and healthy material research all in one research topic related to materials?


Horizon House



University of Denver Career Achievement Center

CASE STUDY 4 | UNIVERSITY OF DENVER CAREER ACHIEVEMENT CENTER A Mass Timber Whole Building Life Cycle Assessment. Scope:

Location: Typology: SF: LCA Type: Life Span: Life Cycle: LCA Tool:

Denver, CO Higher Education - Alumni and Career Counseling Center 21,380 (3 stories) Whole building LCA 100 years A1 - D3 Tally

Question: How do we quantify the embodied carbon of a whole building and reduce its embodied carbon impact? What is the global warming impact of a mass timber structure on the whole building’s embodied carbon? About: Designed to facilitate connections within the DU community, the Burwell Center for Career Achievement is focused on student career development, employer engagement, and alumni activities. Placed in the heart of campus, the Burwell Center boasts open, welcoming spaces and a beautiful patio surrounded by Colorado native landscaping. To help reduce embodied carbon, the building uses a mass timber structure which also contributes to a warm and tactile experience that connects visitors to the natural environment. To further improve the positive environmental impact of the building, the Denver Career Achievement pursued LEED v4. To further address embodied carbon and other environmental impacts, it specifically

University of Denver Career Achievement Center

pursued the Materials and Resources credit “Building LifeCycle Impact Reduction.” To achieve full credit, a whole building life cycle assessment must be performed. Methodology: Tally was used to investigate the cradle-to-grave Whole Building LCA (WBLCA) impact compared to a building baseline over a 100-year time period. A WBLCA typically covers the core and shell, footings and foundations, structural wall assembly from cladding to interior finishes, structural floors and ceilings, roof assemblies, and sometimes parking structures depending on the certification requirements. LEED requires you to do a WBLCA from cradle-to-grave of the project’s structure and enclosure. MEP, site work, and other elements were not included in this study although are ideal to consider when doing a WBLCA if possible.


The first step in running a WBLCA is to create a baseline model so that the design can be compared to a benchmark building. “The baseline and proposed building must be of comparable size, function, orientation, and operating energy performance as defined in EA Prerequisite Minimum Energy Performance. The service life of the baseline and proposed building must be the same and at least 60 years to fully account for maintenance and replacement” (USGBC, 2021). Unlike Energy Use Intensity which offers a database of benchmarks to reference, there is no current database for embodied carbon benchmarking. However, there is promising data collection happening through programs such as the AIA DDX which will begin incorporating embodied carbon into the data reporting process and using that data to support baseline embodied carbon. For now, designers must create their own baseline, which was what was done for this project. The DU baseline building was very similar to our design but included some key differences such as a concrete structure, concrete composite floors, columns and foundations, steel beams and mullions, and a limestone /copper / sandstone façade, etc. The actual built design incorporated lower carbon exteriors such as more brick and slate as well as a mass timber and CLT structure. See table for comparison. Study Results: The LEED WBLCA credit requires you to not only look at GWP but also the many other environmental impact categories such as Ozone Depletion Potential (ODP), Smog Formation Potential, Primary Energy Demand, Acidification Potential, and Eutrophication Potential, etc. In addition, LEED suggests including biogenic carbon in the study. After running the analysis, our results qualified for Option 2, Path 3 which


receives three LEED credits when there is a “10% reduction from a baseline in at least three of the six impact categories, one of which must be global warming potential. No impact category may increase by more than 5%.” Due to the informed material choices and effort for a reduced embodied carbon building, the end results were a 62% reduction in GWP, 52% reduction of acidification, a 2% reduction in eutrophication, and a 53% reduction in smog. One of the biggest challenges of this study was balancing the various environmental impacts, not just GWP. Through this process it was discovered that although using wood products help reduce GWP, wood can increase eutrophication and acidification due to deforestation and logging process of wood (Adhikari, 2018).

Baseline Vs Built LCA Reduction Results -2%


-53% -62%





GWP Reduction Breakdown Baseline to Design 2,500,000




62% Total Reduction



0 Baseline Walls



Curtainwall Mullions

Design Curtainwall Panels



The global warming potential reduction of 62% was a great success for this building. Some of the biggest contributors to the decrease in GWP can be seen in the walls, roof, floors, and structure. For structure, most of the reduction was due to the glulam beams. The roof and floors had a significant reduction due to the CLT. Lastly, the walls saw a significant reduction due to the use of CLT walls and reduction of concrete, limestone, and copper in the façade. Overall, the reduction of concrete and steel through the use of mass timber contributed greatly to the reduction of GWP. Not only did the mass timber products yield low carbon results, but by leveraging this innovative mass timber structural system, the construction schedule was reduced by 6 weeks through the prefabrication and erection of the frame – further reducing the overall construction costs to within $5/SF of a comparable steel structural system. Overall, WBLCAs are an iterative process that allow designers to spot check the building and investigate the best ways to implement a design option. In addition to the whole building overview, this process also helped us better understand the carbon hotspots and see what elements had a positive impact on the design and which elements did not to help implement a lower-carbon alternative.

University of Denver Career Achievement Center

Future Research Questions: 1. How do we begin to calculate other elements not included in Tally such as mechanical, electrical, plumbing, landscape, renewable energy systems, and more? 2. What other environmental impact categories beyond GWP should designers be most concerned about when selecting materials? 3. Does FSC wood decrease eutrophication and acidification impacts compared to generic wood?


36 Soto Building

CONCLUSION Although this investigation just scratches the surface, our firm has gained significant expertise to further develop design strategies to reduce embodied carbon emissions. Each of the featured case studies investigated paths that can work together to reach zero embodied carbon – all of which were made possible by LCA tools. Some of the major lessons learned from this process are: 1.Defining the goal and scope of the project is critical. This is not only helpful for establishing what type of LCA to perform but also for setting clear expectations and comparing against an accurate baseline. For example, even if a certification is not being pursued, a goal of 20% reduction could be made. 2. Start early and iterate. Conducting a LCA, whether on a whole building or a design option, is an effective way to improve the embodied carbon impact of materials used. At the same time, designers should remain skeptical of the carbon findings. There are many variables in calculating embodied carbon, such as where a material comes form, how it is processed, transported, etc. Each variable impacts the carbon outcome and is extremely important when studying design options. Embodied carbon research is still in early stages of development, so we recommend taking every statement and publication with a grain of salt. 3. There is no “rule-of-thumb” for what material is better than another. It depends on many variables. Designers should be running LCAs on design options using the tools that are available today. However, designers need to remain skeptical of the findings and compare various results to

the best solution that accounts for optimal operational and embodied carbon reduction (King, 2018). 4. The 1221 Broadway Lofts case study highlights the importance of first considering re-using a building or materials when looking to reduce embodied carbon. Reusing what already exists can cut down on the cradle to grave carbon impact of a building. 5. Reduce concrete and steel and use carbon sequestering materials when possible. The structural studies show that using wood products helps reduce GWP. However, this is not the case for every wood product, which is why it is critical to source FSC or other sustainably sourced wood and bioproducts. When reducing concrete and steel is not possible, there are smaller initiatives that can be implemented such as adjusting concrete mixtures and optimizing the reduction of materials. Use EC3 to find low-carbon concrete EPDs. 6. There is room for improvement in every part of a building. Wall assemblies, both exterior and interior, can have an enormous impact on a building’s embodied carbon. If you are looking for a low-carbon material, there are plenty of websites to help you do so. Requesting EPDs from manufacturers who may not have them currently available is a way to advocate for future low-carbon products and a lower carbon future. 7. One thing the case studies didn’t investigate is location and transportation of materials. Using local materials is another way to reduce embodied carbon.


Although initiatives discussed in this paper can all contribute to reducing embodied carbon, getting to zero embodied carbon may still require the help of carbon offsets. A carbon offset is “an action or activity (such as the planting of trees or carbon sequestration) that compensates for the emission of carbon dioxide or other greenhouse gases to the atmosphere. (Merriam-Webster, n.d.). These activities can also be commodified for trade to reduce pollutants in the atmosphere. The International Living Future Institute suggests that “one-time carbon offsets must be secured that are equivalent to the total embodied carbon emissions associated with the project scope. Acceptable forms of carbon offsets include Certified Emission Reduction (CER) and Verified Emission Reduction (VER) carbon credits; Renewable Energy Certificates (RECs) are not acceptable. Carbon offsets must be certified by Green-e Climate (www. green-e.org), or an equivalent program” (International Living Future Institute, 2021). 311 Third Off Site Solar


Although carbon offsets are an available option and should be used to offset final amounts, designers should first strive to lower a project’s embodied carbon to the greatest extent possible. The depicted workflow on the right has been created to allow designers at Lake|Flato to investigate embodied carbon on their own. It has primarily been adapted from the Road Map to Reducing Building Life Cycle Impacts (Benke, Walsh, & Lewis, 2019). This investigation only begins to answer the original question: What is the carbon impact of materials being used in Lake|Flato’s projects and how can designers quantify and reduce those impacts? The primary take away from this study is that there are numerous resources and tools available to help us achieve zero embodied carbon. With these in mind, we now have no excuse but to begin to tackle embodied carbon with the same commitment we apply to operational carbon. Our hope is that we inspire designers to ask themselves a similar question that fueled this investigation: “What is the embodied carbon impact of the materials being used in my building and what can I do to reduce it?” It is only by starting with this question that our projects can achieve zero carbon both in operational and embodied emissions.


REFERENCES 2030Challenge. (2021). Interiors. Retrieved from Carbon Smart Materials Pallete: https:// materialspalette.org Adhikari, S. O. (2018). Minimizing environmental impacts of timber products through the production process “From Sawmill to Final Products.” Environ Systems Research. https://doi. org/10.1186/s40068-018-0109-x

Bates, R., & Welch, R. (2014). Performing a Life Cycle Assessment Within a Revit Model. Retrieved from Autodesk University 2014 (AB6328-L). Benke, B., Walsh, D., & Lewis, M. (2019). Roadmap to Reducing Building Life Cycle Impacts. Retrieved from Carbon Leadership Forum.

Architecture 2030. (2021). Insulation. Retrieved from Carbon Smart Materials Palette: https:// materialspalette.org/insulation.

Carbon Leadership Forum. (2020, Apr 18). Road Map to Reducing Building Life Cycle Impacts. Retrieved from Carbon Leadership Forum.

Architecture 2030. (2021). Carbon Impact of Concrete. Retrieved from materials palette. https://materialspalette.org/concrete.

David D. Diaz 1, 2. I. (2018). Tradeoffs in Timber, Carbon, and Cash Flow under Alternative Management Systems for Douglas-Fir in the Pacific Northwest. School of Environmental and Forest Sciences, University.

Architecture2030. (2021). Why The Building Sector? Retrieved from Architecture2030. https:// architecture2030.org/buildings_problem_why/ Architecture 2030. (2020). Carbon Impact of Steel. Retrieved from Carbon Smart Materials Pallet: https://materialspalette.org/steel.


Jassy, Construction. Architecture Section, pages 27-36.

Babor, D. &. (2009). Environmental Impact of Concrete. Bulletin of the Polytechnic Institute of

Elcock, D. (2007). Life-Cycle Thinking for the Oil and Gas Exploration. Argonne National Laboratory. https://www.evs.anl.gov/ publications/doc/LCA_final_report.pdf Eurostat. (2001). Glossary:Carbon dioxide equivalent. https://ec.europa.eu/eurostat.

Gonchar, J. (2020, March). Carbon Crackdown. Retrieved from Architectural Record. www. architecturalrecord.com Hasanbeigi, A. a. (2019). Deep Decarbonization Roadmap for the Cement and Concrete Industries California. San Francisco, CA: Global Efficiency Intelligence. International Living Future Institute. (2021). Zero Carbon Certification. Zero Carbon | Living-Future. org (living-future.org). ISO. (2013). Stationary source emissions — Determination of the ratio of biomass (biogenic) and fossil-derived carbon dioxide. Retrieved from ISO 13833:2013(en). King, B. (2018). New Carbon Architecture: Building to Cool the Climate. New Society Publishers. NOAA. (January 2019). State of the Climate: Global Climate Report for Annual 2018. National Centers for Environmental. Merriam-Webster. (n.d.). Carbon offset. Retrieved from Merriam-Webster.com dictionary.www. merriam-webster.com

ScienceDirect. (2021). Operational Energy. www. sciencedirect.com Simonen, K., Huang, M., X. Rodriguez, B., & Todar, L. (June 2019). Life Cycle Assessment of Buildings Version 1.1. The Carbon Leadership Forum. Tally. (2021). References. Retrieved from Choose Tally. https://choosetally.com/references/. The Carbon Leadership Forum. (2020, May). Taxonomy for Whole Building LCA. www. carbonleadershipforum.org. The International EPD® System. (2021). Environmental Product Declarations. Retrieved from The International EPD® System. www. environdec.com United States Environmental Protection Agency (EPA). (2021). Overview of Greenhouse Gases. www.epa.gov/ USGBC. (2021). Building Life-Cycle Impact Reduction - LEED v4.1. www.usgbc.org/credits.


Lake|Flato Architects 311 Third Street, San Antonio, Texas 78215 210.227.335 www.lakeflato.com


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