Building Sustainable Skyscrapers from Laminated Veneer Lumber
(Page 2 of 3)
Life-cycle analyses comparing the climate impacts of different building materials support Green’s argument, says Ken Skog, a forestry researcher with the USDA Forest Service’s Forest Products Laboratory in Madison, Wisconsin. “Generally the finding has been that if you use wood materials in buildings, you obtain a benefit” over concrete and steel, he says.
But carbon storage in wood products is often less impressive than it first seems, once the entire life cycle of a product is taken into account, notes Ann Ingerson, a Vermont-based economist with The Wilderness Society. “To know whether it actually helps the climate, you’d need to do the accounting, both for the processing chain and in the woods,” Ingerson says. For example, she has found that wood products often get thrown away prematurely, releasing their carbon back into the atmosphere.
Green’s answer is to make tall wood reusable. He compares the large, mass-timber panels that would make up his wooden towers to Lego bricks that can be put together, taken apart, and rearranged—rather than winding up in a landfill at the end of a building’s life. This would ensure that the carbon stored in the panels is truly sequestered for the long term.
Few life-cycle analyses of wood in construction have addressed mass-timber products; most focus on light wood framing, the type of construction used in single-family homes. One recent study, however, by a master’s student at the University of British Columbia, compared construction of a mid-rise office building with concrete to construction with cross-laminated timber and found that the mass-timber building had a 71 percent lower global-warming potential than the concrete version.
Green is quick to add the caution that mass-timber skyscrapers will have environmental benefits only if they’re built of wood from sustainably managed forests. But he says that in some areas of the developing world, increased demand for mass-timber products could actually improve forestry practices by creating an economic incentive for replanting trees—another climate benefit.
To skeptics who question whether wood products can live up to modern fire and earthquake building codes, Green offers a 240-page report that contains detailed technical drawings of his open-source concept. He describes, for example, how in a fire mass-timber panels develop a thin char layer which protects the wood underneath from igniting. And in buildings taller than ten stories, he would add steel cross-beams to provide earthquake and wind resistance.