Several articles have been recently published about the growing number of high-rise buildings constructed mainly from wood. Often these articles fail to address serious risk factors associated with such structures or misrepresent their true impacts on the environment.
The use of cross laminated timber (CLT) for tall buildings is praised for its ability to mitigate climate change because “it removes carbon from the atmosphere”, an assertion that is fundamentally false. To be clear, only living trees sequester carbon from the atmosphere! Harvested and manufactured timber retains only a small fraction of the carbon originally stored in a tree. A recent paper by the Sierra Club (Forests, Wood, Climate) notes that without great advances in forest protection and stewardship, increased wood use that leads to significant increases in deforestation and forest degradation would only deepen our climate problems.
Wood buildings do not absorb carbon from the atmosphere. They store only a fraction of the carbon that was sequestered in living trees. Consequently, it is false to say that building more wood buildings will reverse climate change. Recent research indicates that concrete reverses a portion of the CO2 emissions from the manufacture of cement and permanently sequesters carbon through a process called carbonation. Concrete may well be the only building material that permanently absorbs CO2 and sequesters carbon throughout its useful life and beyond.
At the end of life, wood products will release every bit of sequestered carbon back into the atmosphere through decomposition in a landfill or from burning, also most likely in a landfill. Concrete, however, will continue to absorb CO2 and sequester carbon permanently.
Another misleading issue pertains to wood’s claim of resistance to fire. The implication, however subtle, that a mass timber building offers greater fire protection than a comparable building made of concrete or steel is wrong. No one is safe in a burning building and to suggest otherwise is dangerous and should be censored accordingly. There is much conflicting evidence regarding such claims.
Such evidence was certainly apparent to the National Association Of State Fire Marshals in its official position statement at the hearings for the advancement of Cross-Laminated Timber for the Construction of Tall Wood Buildings (TWB), G75-18, G80-18, and G84-18.
Concrete buildings last longer, do not burn, rot, succumb to termites, are more resilient to natural and man-made disasters, and provide the safest environment for inhabitants.