Feel-good factor: Scientists and architects probe mass timber
Architects and engineers gathered at the offices of Ankrom Moisan Wednesday evening last week to pick away some of the layers of cross-laminated timber.
The material, famed for being strong, lightweight and easy to assemble on construction sites, is still a bit of a mystery to many architects and designers.
Terry Campbell of Sustainable Northwest Wood introduced the speakers who sat on the wooden risers in Ankrom Moisan's lobby/kitchen area which overlooks the Willamette River downtown. The subject was Mass Timber Buildings — How Eco-friendly are they?
A vice president at Ankrom Moisan, Murray Jenkins, first explained how the firm looked at 25 properties around town when it wanted to relocate from Macadam Avenue. They loved the unfinished wooden warehouses they saw but were constantly outbid on the leases. Working with Gerding Edlen they were able to design and deliver their current mixed-use building, built from scratch, at less than the cost of a steel and concrete one.
Campbell said they had evaluated CLT panels but in the end used three-inch decking over glulam beams. The wood, he was proud to say, was from northwest forests and was milled fairly locally, in Washington.
"The employees love it, it's been great," he said. He reported that in a recent post-occupancy survey, workplace satisfaction had risen from 58 percent at the Macadam space to 77 percent at the new space.
The talk addressed two issues:
One: "Mass timber relies on small pieces of wood glued together for structural performance. Some skeptics suggest that small pieces of wood typically come from forests that are managed on a shorter harvest rotation. Short rotations do not allow forests to mature or provide other ecosystem services, which can be detrimental to the health of forests and for the services they provide."
And two: "Gluing lots of wood together for indoor spaces increases the amount of potential off-gassing products to which workers and inhabitants are exposed."
Dr. Norm Johnson, a forestry professor at Oregon State University, said that he and a friend Jerry Franklin had tried to run a sustainable forest but it was hard. He brandished a new book, Ecological Forest Management, which he coauthored with Franklin and Debora L. Johnson.
"Is wood eco-friendly?" Johnson asked. "Of course, you say. But nothing in forestry is quite that easy."
He said that all forestry books since the first, written in 1917, use an economic foundation, but theirs is the first to use an ecological foundation. He stressed the importance of biodiversity and protecting habitats as much as churning out board feet. He also noticed that for all his efforts, "I still got tree sitters."
"I'm 76, this is my last bite of the apple," he joked, talking about trying to let forests grow for 80 to 100 years instead of less, and the importance of letting pre-forest grow naturally after a fire or a harvest and before planting.
Johnson wants foresters to harvest in a more patchy manner than the big clear-cuts you see today, so the forest can grow back quicker and more diverse.
To him the term "healthy forest" has lost its meaning.
"Oregon has fallen behind other states. California and Washington now have a closer match to ecological forestry," he said.
"I go to CLT rallies with these pictures from Great Britain of fabulous mass timber buildings, talking about how much they've contributed to [reducing] climate change by how many cups of tea they've saved, in terms of energy expenditure. The jury is still out on this. The substitution effect (how leaving a tree up sequesters carbon that might otherwise damage the environment) is an intricate set of calculations."
He concluded that it is better to use wood on a sustainable basis than let forests grow, but this means harvesting on longer rotations. An audience member asked if letting forests grow takes into account the bigger fires and carbon emission that can follow.
Surprisingly Johnson said fires were not that big of emitters of carbon: most of the carbon is in the soil and the bowl of the trees and remains there after the fire.