Miller Hull

Mass timber seems alluring because of its low carbon footprint, but not all wood is equally sustainable. We dig deep into the controversy over which types of timber are “climate smart.”

By Paula Melton

When Michigan State University started planning its new STEM building, the design team was considering a typical concrete or steel structure. That was before Richard Kobe, Ph.D., heard about the project. Kobe, who heads up the university’s Department of Forestry, advocated for a mass timber structure instead.

After a field trip to a cross-laminated timber (CLT) factory and a cost-benefit analysis showing that mass timber would cost about the same as conventional materials, the university made its choice: mass timber it was. “There were aesthetic considerations and sustainability considerations,” Kobe told BuildingGreen. “Most of what we talked about was carbon storage and avoided emissions. That was enough to nudge university leadership over the hump in building the first building in the region of this type.” According to Nordic, the glulam manufacturer for the project, the building is storing 1,856 metric tonnes of CO2 equivalent. That’s like taking 400 cars off the road for a year—and doesn’t account for the emissions that were avoided by using wood instead of concrete or steel.

The building is unusual because it houses wet labs requiring fume hoods and other specialized infrastructure, which involved detailed mapping in order to avoid penetrating the structural wood members. It is also built on the remains of a decommissioned coal power plant on campus. “There’s this juxtaposition with what historically was burning coal, which obviously led to lots of CO2 emissions,” Kobe said.

Some version of this story is increasingly familiar within the green building community. Mass timber is lauded for being “climate smart”—meaning it helps mitigate climate change—because it stores carbon from the atmosphere instead of emitting carbon.

But is this story true?

Some researchers are starting to suggest that we look deeper. They say that the traditional way of tracking the greenhouse gas emissions of products—through life-cycle assessment (LCA)—has flaws, and that we need to scrutinize various types of forestry practices in order to distinguish climate-smart wood from less climate-smart products (including net emitters).

This report looks at the assumptions behind LCA, as well as newer research methods, and suggests real-world actions you can take while the scientists work out their differences. It is the second in a series on embodied carbon; the first report, The Urgency of Embodied Carbon and What You Can Do about It, is available to read online and to download as a Spotlight Report.

LCA of Wood Products

Consider another story about mass timber and carbon.

“We have a client who was looking at mass timber; they had typically done steel,” recalled Kristen Dotson, sustainability services director at the Miller Hull Partnership. “We were super excited because of course we love mass timber.”

Then the client started asking about embodied carbon. They wanted to compensate for removing a grove of trees where the project would be built—“not necessarily replace the function, but mitigate the harm we’ve done by removing that forest.Aesthetically and ecologically, they wanted to be ‘of the forest.’” The process started with whole-building LCA using the Revit plug-in Tally. “Tally always tells you that wood is good,” said Dotson.But having heard other experts’ conversations—conversations suggesting that LCA was too limiting because it can’t account for the climate effects of different forestry practices—she became concerned that the Tally results were not adequate. Miller Hull teamed up with a local nonprofit, Ecotrust, to attempt a new kind of analysis. The results threw a wrench into the whole project.

Read the full story at BuildingGreen