October 7, 2019 – A new Backgrounder has been added to the Building resilience Coalition website that sets the record straight about the use of mass timber for tall buildings.
As noted by the authors of the Backgrounder, there is a great deal of misrepresentation on the web about the environmental and climate-related benefits of mass timber use for high-rise buildings.
Many of these articles fail to address serious risk factors associated with such structures or misrepresent their true impacts on the environment.
They often extoll the supposed virtues of tall timber buildings noting that structures built using cross-laminated timber are an “environmentally sustainable alternative to concrete and steel, which generate large quantities of greenhouse gases in their production.”
It is often asserted that construction of cross-laminated timber high-rises emits roughly 25% less carbon dioxide than concrete, and such buildings store atmospheric carbon locked in the trees used to build them, which over time will be replaced by new trees that will absorb carbon dioxide.
For those unfamiliar with the term, cross-laminated timber is a form of engineered wood where pieces of wood are glued together to create a panel that is stronger than an ordinary wooden beam. This is a relatively new building product, but it is gaining popularity in North America in large part due to intense lobbying efforts by proponents in the architectural community and in the wood products sector.
The use of mass timber for tall buildings is touted for its power to mitigate climate change because they remove carbon from the atmosphere, an assertion that is fundamentally false.
As noted in the Backgrounder, living trees sequester carbon from the atmosphere. Harvested and manufactured timber retains only a small fraction of the carbon originally stored in a tree. Most of the tree’s carbon remains behind in the forest soil or is lost in the leaves and bark usually left to rot on the ground or is burned as biofuel. Far less than half the carbon of a living tree ends up as a long-lasting building product. The rest is emitted back into the atmosphere.
The atmosphere really does not differentiate whether the emission is from “green carbon” or black carbon. Carbon is carbon!
It also is argued that carbon lost from harvesting sustainably managed forests is balanced by the absorption of carbon from new forest growth. Indeed, this is the basis of the carbon neutrality rule in international carbon accounting metrics that says carbon losses from harvesting trees are not counted in emissions statistics because somehow, they will be offset by new forest growth elsewhere.
The problem is that not all forests are sustainably managed, and even then, research indicates it can take over a hundred years before new forest growth will replace even half of the original carbon lost. The key point is that wood buildings do not absorb carbon from the atmosphere so it is false to say that building more wood buildings will reverse climate change.
Cutting down more trees – the only effective natural means for absorbing atmospheric carbon – to make more mass timber structures is not a sound adaptive strategy for dealing with climate change.
The backgrounder was prepared by William Larson, Vice President Marketing at CalPortland, and Frank Came, Managing Director, Globe Advisors.
Read the full Backgrounder here.
