Let’s fill our cities with taller, wooden buildings
Editor's note: The following op-ed by Fellow Frank Lowenstein and colleagues was first published in the New York Times.
Across North America, trees stand ready to help us solve the climate crisis. Trees remove carbon dioxide from the atmosphere and store it in their wood. One way to respond to a challenge from the United Nations secretary general, António Guterres, to seek “bold action and much greater ambition” on climate change is to protect forests from development, improve forest management and use sustainably harvested wood to build tall buildings. This will allow us to pump carbon from the atmosphere and store it both in forests and in cities. It will also support rural economies, improve wildlife habitat and create more affordable housing.
This opportunity arises from cross-laminated timber, or CLT. First introduced in the 1990s, it enables architects and engineers to design tall, fire-safe and beautiful wood buildings. Recent examples in the United States include the eight-story Carbon12 building in Portland, Ore. and a six-story dormitory at Rhode Island School of Design in Providence. In Canada, Norway, Sweden, England and Australia, even taller wooden buildings are already in use. The Mjosa tower in Brumunddal, Norway, is only 25 feet shorter than the Statue of Liberty.
Private industry is gearing up to provide engineered wood for more tall wood buildings here in the United States. This year a highly automated, large CLT plant opened in Washington state. Last week, the first ever CLT plant in New England was announced in Maine.
The energy embodied in the materials for new buildings around the world — mostly steel and concrete — accounts for 11 percent of global carbon emissions. Typically, coal is used to heat these materials to temperatures over 2,500 degrees Fahrenheit in the manufacturing process.
Wood, in contrast, is forged from sunlight. A study by scientists from Yale University and the University of Washington showed that expanding wood construction while limiting global harvesting to no more than the annual growth could produce a combination of emissions reduction and carbon sequestration equivalent to eliminating construction emissions altogether. This could take a big bite out of the carbon problem, roughly equivalent to the present contribution from all types of renewable energy.
One study conducted by researchers in British Columbia found that building a five-story office building with wood had less than a third of the global warming impact when compared with a steel and concrete building of the same size. Beyond taking less energy to produce, wood buildings store carbon that otherwise would have returned to the atmosphere as those trees died and began to decay. The wooden structure of the new 18-story Brock Commons dormitory at the University of British Columbia, for example, stores 1,753 metric tons of carbon dioxide. That carbon will be locked up for decades, if not a century or more, until the building is torn down, and if the wood is reused, perhaps even longer.
Additional benefits come from the fact that these new wood technologies make it affordable to construct mid-rise housing of six to 12 stories. Conventional wood framing is limited to five stories by building codes, or six stories if a concrete first floor is included. The high cost of materials and construction — for example, renting a tower crane and hiring someone to operate it — usually push developers working to construct steel and concrete housing to design and build structures of more than 12 stories to provide a suitable return on investment.
Transportation hubs in the inner suburbs of cities in the United States are often surrounded by multifamily housing of only five or six stories. With CLT, those buildings could be taller, creating more housing close to trains, subways and buses, and a more compact urban development pattern. That would save forests on the urban fringe from being cut to make way for more housing, and cut emissions and congestion on highways. Taller mid-rise wood buildings would also help lower the cost of housing by increasing supply.
To stabilize climate and support the wood building revolution, we need to stop the conversion of forests to other uses — whether to pastures in the Amazon or to shopping malls, houses and solar arrays near Amherst, Mass. When forests are cleared for housing or other land uses, the carbon stored in the forest is typically released to the atmosphere, and the ability of the forest to capture future carbon is lost.