Measuring a building’s embodied carbon

Photo © Chad Davies
Photo © Chad Davies

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.

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. 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 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 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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