Building with wood is part of the solution to fight climate change. It’s written in black and white in the IPCC reports, and there’s a reason for it.
Trees grow by taking CO2 from the air. Through photosynthesis, they capture CO2 and convert it into wood. In other words, wood is CO2 in a cage. “Generally speaking, a cubic metre of wood contains a tonne of CO2 equivalent,” says Jean-François Boucher, a professor at the Université du Québec à Chicoutimi and member of the Centre for Forest Research. When trees are cut to make 2x4s or beams, this stored CO2 remains sequestered in the wood and therefore in the building made of wood.
Yes, but if the forest is cut, the trees are no longer there to do photosynthesis and continue to capture CO2, you might say. That’s true! But the forest will grow back, and it doesn’t have to be at full maturity to capture CO2. In fact, it’s the opposite. It is during their growing phase, when the trunk thickens and the branches grow longer, that trees absorb the most CO2.
A forest floor can be cut, but floors in other areas are growing, and the forest heritage is maintained or even growing throughout the territory.Jean-François Boucher, professor at the Université du Québec à Chicoutimi
The idea is not to cut the forest faster than it grows, so that the sequestered and cut CO2 does not exceed the CO2 captured by photosynthesis. “A forest floor can be cut, but floors in other areas are growing, and the forest heritage is maintained or even growing throughout the territory,” said Jean-François Boucher. In principle, with sustainable forestry practices, the forest is carbon neutral.
In principle, sure, but in practice? According to Canada’s GHG inventory, produced annually by the federal government under the United Nations Framework Convention on Climate Change, Canada’s forest is a carbon sink. From 1990 to 2015, the forest’s carbon footprint, despite logging, was positive. Jean-François Boucher assures us that the negative results of recent years are circumstantial. The culprit is the mountain pine beetle in western Canada that led to the premature death of trees.
Let’s take this a step further, because we don’t construct buildings with actual trees, but with beams, columns, 2x4s, etc. Making these materials requires energy and therefore emits GHGs. The question is whether manufacturing these wood materials generates more or less GHGs than if they were made from steel or concrete. The answer is given by GESTIMAT, a tool for calculating GHG emissions from the manufacture of materials that make up the structure of a building. Yannick Lessard, project manager for GESTIMAT at Cecobois, did the calculations for several buildings, including the light-frame expansion of the Fernand-Seguin school and the Origine residential tower with its 12 floors of mass engineered timber. His general finding is that the manufacture of structural components from wood rather than steel or concrete reduces GHG emissions by 50%.
And in the context of climate change, the opportunities offered by wood are good news!