Building Materials Matter

Life cycle view supports informed choices, contributes to sustainable design
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Carbon Footprint: Reducing Greenhouse Gases

Although there is growing awareness that using wood from sustainably managed forests can reduce a building’s carbon footprint, only a portion of wood’s benefits are recognized in an LCA.

As noted, the LCA literature review concluded that fossil fuel consumption and potential contributions to the greenhouse effect tend to be minor for wood products compared to competing products. This is because wood products require less energy to manufacture than other major building materials, and most of that comes from renewable biomass (e.g., sawdust, bark and other residual fiber).3

The other aspect to wood’s carbon footprint is that as trees grow they absorb carbon dioxide (CO2) from the atmosphere, release the oxygen (O2), and incorporate the carbon into their wood, leaves or needles, roots, and surrounding soil. Young, vigorously growing trees take up carbon quickly, with the rate slowing as they reach maturity (typically 60-100 years, depending on species and environmental factors). Over time, one of three things then happens:

  • When the trees get older, they start to decay and slowly release the stored carbon.
  • The forest succumbs to wildfire, insects, or disease and releases the carbon quickly.
  • The trees are harvested and manufactured into products, which continue to store much of the carbon. (Wood material is approximately 50 percent carbon by dry weight.) In the case of wood buildings, the carbon is kept out of the atmosphere for the lifetime of the structure—or longer if the wood is reclaimed at the end of the building’s service life and reused or manufactured into other products.

Unless the land is converted to another use, the cycle begins again as the forest regenerates and young seedlings once again begin absorbing CO2.

For more information, the USDA Forest Service recently released an infographic illustrating the forest/carbon cycle (www.fs.fed.us/climatechange/advisor/scorecard/Carbon_Infographic_Final.pdf).

 

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Originally published in Architectural Record

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