Measuring a building’s embodied carbon

by sadia_badhon | October 30, 2020 10:07 am

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by Edie Sonne Hall

From an environmental point of view, it is widely known buildings matter, as they consume nearly half the energy produced in the United States, use three-quarters of the electricity, and account for nearly half of all carbon dioxide (CO₂) emissions[2].

The magnitude of their impacts is the driving force behind many initiatives to improve tomorrow’s structures—from energy regulations and government procurement policies to green building rating systems and programs such as the Architecture 2030 Challenge[3]. The focus on energy efficiency, in particular, has led to widespread improvements, so much so many designers are now giving greater attention to the impacts of structural building materials. Additionally, clients are increasingly seeking real estate that meets or exceeds green building codes or carbon policies, creating almost $25 trillion in business opportunities[4] between now and 2030.

The ability to understand and measure a building’s environmental impact is pivotal as we work to make buildings more sustainable. By exploring the principal methods and tools assessing carbon footprint in the context of building materials, architects and specifiers can compare alternate designs and make informed choices.

Measuring carbon footprint in building materials

A building’s carbon footprint includes both embodied and operational carbon. Embodied carbon refers to the emissions associated with manufacturing a product, while operational carbon describes the emissions of CO₂ during the operational or in-use phase of a building.

Embodied carbon of different materials can be compared if they have the same functional equivalency, meaning they provide the same service for the same length of time. The difference between these two values is referred to as the substitution benefit, which refers to the avoided emissions achieved by using the lower embodied carbon material.

Life-cycle assessment

Life-cycle assessment (LCA) is an internationally recognized method for measuring the environmental impacts of materials, assemblies, or whole buildings, from extraction or harvest of raw materials through manufacturing, transportation, installation, use, maintenance, and disposal or recycling. While LCA is sometimes described as cryptic and complicated, it is simply a thorough accounting of resource consumption, including energy, emissions, and wastes associated with the production and use of a product.

WOOD’S DUAL ROLE IN CARBON REDUCTION

Wood tends to have lower embodied carbon, as it requires far less energy to manufacture than other materials, and very little fossil fuel energy, since most of the consumed energy comes from converting residual bark and sawdust to electrical and thermal energy.* For example, the production of steel, cement, and glass requires temperatures of up to 1927 C (3500 F), which is achieved with large amounts of fossil fuel energy. Wood also consists of about 50 percent carbon by dry weight, and wood in a building provides operational carbon benefits in the form of physical storage of carbon that would otherwise be emitted back into the atmosphere. In a wood building, the carbon is kept out of the atmosphere for the lifetime of the structure, or longer if the material is reclaimed and reused or manufactured into other products. * Referenced from “A Synthesis of Research on Wood Products and Greenhouse Gas Impacts,” FPInnovations, 2010.

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Whole Building LCA (WBLCA) tools

A myriad of tools assess material choices for sustainability benchmarks. Whole building LCA tools use life-cycle inventory at the individual system level (e.g. flooring, wall) or for entire buildings. These tools are accepted in many green building certification programs, including Leadership in Energy and Environmental Design (LEED) and Green Globes.

Athena’s Impact Estimator for Buildings provides access to life-cycle data[6] without requiring advanced skills. It can model more than 1200 structural and envelope assembly combinations, allowing for quick and easy comparison of design options. Users input basic information about building geography, size, and height, and a model is developed by creating a series of assemblies, such as walls, floors, and roofs. Alternatively, users can import a bill of materials from any computer-assisted design (CAD) program. These materials are used to create a life-cycle inventory, and are assessed using the Tool for the Reduction and Assessment of Chemical and Other Environmental Impacts (TRACI) methodology (TRACI is a life-cycle assessment [LCA] methodology developed by the U.S. Environmental Protection Agency [EPA] and the most commonly used method in North America). Results[7] can be summarized by assembly group and life-cycle stage, with final reporting on greenhouse gas (GHG)-related impacts.

Commercial license tools, such as Tally and Oneclick, integrate architect and engineer software to assess environmental impacts of building material lists. Tally pulls its material life-cycle inventory information from GaBi, an international life-cycle inventory database, and Oneclick relies on published environmental product declarations (EPDs), which some experts warn may not be well suited for whole building LCAs due to inconsistencies across product categories.

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Other tools may be helpful after the building has been designed. For example, the Embodied Carbon in Construction Calculator[9] (EC3) facilitates the comparison of EPDs within the same material categories. It is currently in beta form and work is being done to properly characterize wood EPDs.

The Carbon Calculator for Wood Buildings[10] focuses on the volume of structural wood in a building, then estimates how much carbon is stored in the wood, the GHG emissions avoided by not using steel or concrete, and the amount of time it takes North American forests to grow that volume of wood.

The product level

The ability to assess the environmental impact of a building ultimately rests on the life-cycle information for each component material. However, sometimes stakeholders just want this information at the product level.

An EPD is a standardized, third-party verified label that communicates the environmental performance of a product to industrial and end-use consumers. An EPD is based on an LCA report, and includes information about both product attributes and production impacts. The nature of EPDs also allows summation of environmental impacts along a product’s supply chain—a powerful feature enhancing the utility of LCA-based information.

FOREST CERTIFICATION

Forest certification assesses a landowner’s forest management against a series of agreed standards related to water quality, biodiversity, wildlife, and forests with exceptional conservation value. Wood is one of the few building materials that have third-party certification programs in place to demonstrate products being sold have come from a responsibly managed resource. As of 2020, more than 243 million ha (600 million acres) of forest in the U.S. and Canada were certified under one of the four internationally recognized programs employed in North America.* * Consult the Intergovernmental Panel on Climate Change (IPCC) Special Report on Climate Change, Desertification, Land Degradation, Sustainable Land Management, Food Security, and Greenhouse gas fluxes in Terrestrial Ecosystems.

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What can wood EPDs tell us

Earlier this year, the American Wood Council[12] (AWC) and Canadian Wood Council (CWC) published updated cradle-to-gate EPDs for six of the major North American wood products (softwood lumber, plywood, oriented strand board [OSB], laminated veneer lumber [LVL], I-joists, and glue-laminated [glulam] timber).

Wood EPDs are underpinned by the biogenic carbon cycle—in product storage, energy for manufacturing, as well as impacts in the forest. A cycle, by its very nature, is not linear and not well suited for LCA. The complexity of the biogenic cycle warrants detailed explanation.

Difference between biogenic and fossil carbon

As trees grow, they clean the air by absorbing CO₂ from the atmosphere. Trees release the oxygen and incorporate the carbon into their twigs, stems, roots, leaves or needles, and surrounding soil. As trees mature and then die, they start to decay and slowly release the stored carbon back into the atmosphere.

This is a closed loop cycling through natural processes of growth and decay. It is also a closed loop cycle when forests are harvested for use in products or energy. The biogenic carbon cycle fundamentally differs from the open/one-way flow of fossil carbon to the atmosphere.

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How would an increase in demand for wood products impact forests?

Many builders and architects are concerned with the impact of increased demand for wood products on forests. Through both empirical evidence as well as economic models, the authors have found demand for wood products results in more forest land, not less. Markets provide economic justification for sustainable forests and good forestry practices.

Responsibly managing forests in a way that balances harvesting and replanting can maintain a large pool of sequestered carbon over the long term. It also provides a sustainable source of wood products that continue to store carbon and offset the use of fossil fuels, hereby reducing atmospheric GHGs.

In terms of resource availability, the U.S. Forest Service’s Forest Inventory Analysis[14] program tracks the volume and health of forests. In 2018, U.S. forests and harvested wood products were a net sink on the order of 663 million metric tons CO₂e, which offsets about 10 percent of the nation’s GHG emissions.

The amount of forest area has remained constant since about 1900, and U.S. forests have been net sequesters since the 1950. During this same period, harvests have remained stable[15] or in some cases have increased, such as in the southern parts of the country.

Wood supports a sustainable future

While no one material is the best choice for every application, LCA studies have consistently shown wood has a favorable environmental profile compared with functionally equivalent products. As with any building project, different materials have their own unique trade-offs and benefits based on a project’s design objectives. By understanding the terminology and by using the right tools, the architect’s material assessment—and resulting client communications—can tell a compelling story of a building’s reduced carbon footprint.

[16]Edie Sonne Hall is founder of Three Trees Consulting, where she provides technical expertise to projects involving forest carbon accounting, ecosystem services, green building, life-cycle assessment (LCA), and sustainable forest certification. She serves as facilitator of the North American Wood Products LCA Coordination group, which is made up of wood product LCA experts, representing academia, government agencies, industry associations, and consultants in the U.S. and Canada.

Source URL: https://www.constructionspecifier.com/measuring-a-buildings-embodied-carbon/

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