Forest Service study promotes wood as a “Green Building Material”, but not all agreePosted: October 10, 2011
Nevertheless, the U.S. Forest Service has published a study arguing the American building industry has overlooked that fact. Its authors want more recognition of how wood takes less energy to fabricate, releases less carbon into the atmosphere and is structurally comparable to steel and concrete for many kinds of construction.
“We know there’s economic competition between materials,” said Ken Skog, one of the study’s authors at the Forest Service’s Forest Products Laboratory in Madison, Wis. “As people are concerned about the environmental performance of materials, those materials that emit less should be a factor.”
Or as Bozeman architecture professor Ralph Johnson put it: “The bottom line is we often do need to be reminded of the obvious.”
Johnson studies sustainable building practices and directs the Wheeler Center at Montana State University. He said wood has lost status in many “green building” standards because of its relatively short lifespan compared to steel and stone. The standard-makers also knocked it on the assumption we cut more wood for houses than our forests could reproduce.
“There’s no one product that’s inherently more sustainable than any other product,” Johnson said. “Using steel – it’s a great product, it gets lot of points in LEED (the Leadership in Energy and Environmental Design standards). But it has a tremendous amount of embedded energy and it’s never local.”
And according to research cited in the Forest Service report, a house built of wood produced 26 percent less greenhouse gas emissions than a comparable home made with steel framing, after all the harvesting, transportation and refining processes were taken into account. A stick-built house had 31 percent less emissions than one made with concrete framing.
As for carbon, the report cited a study in the journal Environmental Science and Technology that found each ton of carbon in lumber used in place of non-wood products reduced greenhouse gas emissions, by 2.1 tons of carbon. Houses with wood-based walls needed 15 percent less energy for manufacturing than similar houses with steel or concrete structures.
“Existing materials are good and we should be affirming the fact,” Skog said. “We need to be educating engineers, builders and architects, and wood needs to be recognized in various (building) codes.”
The trusty 2×4 stud has been a mainstay of home construction for generations. But steel beams and concrete panel construction dominate commercial and high-rise buildings. While innovations in laminated wood beams and panels have made inroads, Missoula architect Marty Noyd said current practices will be tough to change.
“A lot of older buildings in downtown were all built out of wood and masonry,” said Noyd, co-owner of OZ Architects. “But the building code allows you to build a bigger taller building , and gives you other exceptions when you use materials that are noncombustible. The Garlington (Lohn and Robinson) building couldn’t use wood, because it’s got to be fire-resistant construction. Any hospital over one story needs to be fire-resistant.”
Noyd said the switch to milling lumber out of small-diameter trees has also brought new problems. Those studs are less dense than old-growth lumber, and tend to warp and deform.
“We just had this three-day period of rain,” Noyd said. “Wood absorbs moisture, and when the weather changes it starts to dry out. Then we see a lot of issues. You get shrinkage, cracks in sheetrock, nails pop out. Wood will swell, and steel won’t.”
Kevin Gordon of Missoula-based Gordon Construction said building codes dictated more steel than wood for commercial projects. And over time, steel’s become the go-to material.
“A lot of our guys are used to using steel studs,” Gordon said. “And steel is one of the most recycled products in the world.”
Even so, the report puts particular emphasis on finding markets for beetle-killed forests, which tend to be in small-diameter lodgepole pine stands.
“In the Rockies alone, we have hundreds of thousands of dead trees killed by bark beetles that could find their way into the building supply chain for all types of buildings,” Forest Service Chief Tom Tidwell said in a statement about the report. “Taking a harder look at wood as a green building source could reduce the damages posed by future fires, maintain overall forest health and provide much-needed jobs in local communities.”
Solid wood products supported 350,000 direct U.S. jobs and $12 billion in payroll in 2009, although those figures were down 460,000 jobs and $15.6 billion in 2008. Skog said the national recession drove those numbers down, and a renewed interest in wood could help bring them back up.
Three things the Forest Service plans to do in that regard include:
Perfecting a “life cycle assessment” standard that would show how much energy went into a piece of lumber and how much emissions were released in its manufacture. That could be compared to measurements for steel or concrete, like consumers now use Energy Star ratings in comparing appliances.
A WoodWorks campaign funded by private companies, the Forest Service and other groups, aimed at getting architects and engineers to use more wood. The report estimated that a five-year national effort could increase wood use volume by 5.5 billion board feet and save 30 million metric tons of carbon dioxide.
More research in developing better wood construction materials or techniques like cross-laminated timber.
Some Missoula projects have already experimented with those new technologies, according to Noyd. The Rocky Mountain Elk Foundation’s headquarters used beams made of small-diameter trees bonded together. And Sussex School’s new building earned a gold certification from the national Leadership in Energy and Environmental Design (LEED) rating system for its all-wood construction.
“We used locally grown wood, that was milled here,” Noyd said. “You get points for that, if you can get it within 500 miles of your building site. For small-scale buildings, there are advantages.”