Brian Brashaw, U.S. Forest Service Assistant Director – Wood Innovations, State & Private Forestry.
As the need to address the challenges posed by climate change become more urgent and our population increases, we must prioritize utilization of climate-friendly and sustainable structural materials. Wood is the leading solution.
There is a myriad of ways a building’s carbon footprint can be reduced. In addition to designing in more efficiency, material choices can have significant impacts on the overall carbon footprint of the structure. Choosing to use North American wood products is a material choice that will not only reduce the building’s carbon footprint, but it is also the only primary building material derived from a renewable resource.
Research shows that wood is far better for the environment than materials that consume intensive amounts of energy (often from non-renewable fossil fuels) during the manufacturing process. Specifying North American wood products ensures the material was made under strict environmental and labor regulations, and that the product did not require the same intensive energy production to make.
Carbon accounting for buildings is complicated, and depending on the chosen approach, can significantly influence material choices. Most approaches focus on a measurement of “embodied carbon” in a building, which is the measure of the Global Warming Potential (GWP) based on carbon emissions associated with extraction, transportation, manufacturing, use, and end-of-life outcome. Simply put, it’s the total GWP emissions released into the atmosphere from a material’s life cycle as determined by a life cycle assessment.
Stored carbon in building materials, or “stored carbon,” should also be credited in calculating the total carbon benefit of materials. North American wood products, unlike any other primary building material, hold carbon for the duration of a building’s life (and longer if building components are reused instead of demolished). As trees grow, they pull carbon from the atmosphere. This carbon is retained in the wood that is then transformed into wood products. Developing a consistent, transparent and robust method for accounting for stored carbon in wood products is a priority.
50 percent Carbon by Dry Weight
Depending on end-use and service life conditions, wood products can store carbon for many decades or longer, providing long-term climate benefits for people worldwide. For example, the Horyuji Temple in Japan is one of the world’s oldest wooden buildings and was constructed in 607 A.D.
Specifying structural wood and wood finishes in buildings ensures the carbon being stored in the product does not enter the atmosphere during the lifetime of the structure—even longer if the wood is reclaimed/reused.
As one example, carbon emissions can be lowered by as much as 20 times by simply installing wood flooring instead of vinyl.
A Comparative Life Cycle Assessment Study
A recent study compared the Life Cycle Assessment (LCA) of an 8-story above-grade, nonresidential structure with 3 stories of below-grade parking located in the Pacific Northwest. Three construction material scenarios were evaluated: a traditional reinforced concrete building, two using cross-laminated timber (CLT) and glulam, one using gypsum wallboard, and one using exposed wood for fire resistance.
The study considers extraction, transportation, manufacturing, and construction transportation and installation. The study found that:
- An average of a 26.5% reduction in Global Warming Potential was observed in the two CLT-glulam scenarios. This doesn’t even include the benefit of the carbon stored in the wood.
- The embodied fossil energy was 8% lower in the CLT-glulam scenarios.
- An additional 1,556 to 2567 tons of CO2c (biogenic) is stored in the structure of the CLT-glulam building scenarios with and without gypsum wallboard protection, respectively.
North American wood products are not only resilient and reliable building materials, but they are also good for the planet today and into the future.