The International Institute for Sustainable Development has released a report challenging the perceived sustainability of wood, calling into question methods of measuring carbon footprint.
The report reads: “Whereas emissions from the production of concrete and steel are well understood, accounting for emissions and sinks in the biogenic carbon cycle of wood products is complex.” Biogenic carbon cycle, as it pertains to wood used in homes, refers to both the emissions expelled from trees during the felling of a forest and/or during the ultimate end to the wood’s lifespan (i.e., the dump or burning). When accounted for by the report’s researchers, the overall carbon footprint of lumber exceeds that of concrete. “Think of how much lumber you actually produce from a whole tree,” says Seton Stiebert, the report’s lead author. “There is biomass that is left at the site, sawdust and other wood waste that is typically combusted for heat as well as potential losses from below-ground and soil carbon pools, that may not fully regenerate in the forest to the same levels.”
The long-term solution, Stiebert explains, is improved forest management and replenishing. “The biggest loss of biogenic carbon occurs in the cases where wood is extracted from a natural forest that has never been harvested before,” he says. The big loss comes in the 60 years or so it takes for those forests to regrow, when they’re not taking carbon out of the air.
A more immediate, albeit less impactful, method of reducing wood’s biogenic carbon impact is reclamation—a topic discussed in this issue (page 38).
“Reclaiming wood at the end of life of a building can reduce overall lifecycle emissions of wood products,” Stiebert says. “It keeps the biogenic carbon in the lumber from being released ... This could mean that the biogenic carbon isn’t released for about another 20-50 years, depending on the re-use application and then what happens after that use.”