Story at a glance
- Cross-laminated wood is becoming a hot new building material with several benefits, including storing carbon dioxide.
- Timber towers are under construction, up to 35 stories.
- Can our forests sustain future timber cities?
An 18-story apartment building in Brumunddal, Norway, is not only the world’s tallest timber building, it’s also the world’s tallest carbon dioxide sink. The building’s timber structure, including elevator shafts, are made entirely from cross-laminated timber with columns made from glued-laminated timber. The same materials will be used for a massive 500,000 square-foot timber office complex on the waterfront of Newark, New Jersey. In Sweden, a new development in Stockholm will see 31 timber towers rise 25 to 35 stories from the waterfront to house 3,000 apartments and 30 shops and restaurants.
Wood, or more specifically cross-laminated timber (CLT), is the hot new building material due to its high strength-to-weight ratio, precise prefabrication in a factory and ease and speed of assembly on building sites. Designers also say timber buildings can be a powerful tool in the struggle to reduce global carbon dioxide (CO2) emissions.
Double benefits for climate protection
Trees absorb CO2 from the atmosphere as they grow and will release it if the tree decays or is burned. However, if the wood is used in a building that CO2 could be locked away for many decades, or even hundreds of years, said Galina Churkina of the Yale School of Forestry and Environmental Studies. Such timber buildings are carbon sinks — a place that keeps CO2 from getting into the air. A second benefit from using wood as a building material is that it reduces the amount of cement and steel production, both of which are large CO2 emitters.
This matters because an enormous number of new buildings will be built as there will be 2.3 billion more people living in urban areas by 2050, according to UN estimates. If these future buildings are made of concrete and steel they may use up 20 percent of our remaining carbon budget to keep global warming below 2 degrees Celsius, according to a study by Churkina and colleagues published Jan. 27 in the journal Nature.
However, if most of these new buildings are made from wood they could store close to 700 million tons of CO2 every year. In addition, this would reduce cumulative emissions from steel and cement manufacturing by half.
“We need to keep CO2 on the land and out of the air. Building timber cities can help,” Churkina said in an interview.
CLT is an engineered wood product that is sometimes called mass timber. It’s prefabricated using several layers of kiln-dried lumber, laid flat-wise and glued together in alternating layers which makes it far stronger while being light. Not only is CLT a better insulator, it is more fire resistant — rather than burning, it chars.
Keeping climate change under 2 degrees Celsius means there can be no CO2 emissions by 2050 without ways to remove it. “We can’t get rid of most of the CO2 from concrete and steel production,” she said. That makes reducing the need for such materials and finding ways to remove CO2 from the air extremely important.
A five-story residential building structured in laminated timber can store up to 180 kilograms (396 pounds) of carbon per square meter, according to the study. That’s three times more than trees in a similar sized area of forest would naturally store. So that 500,000 square-foot timber office complex in Newark, N.J., may end up being a permanent storage site for around 8.4 million kilograms (18.5 million pounds) of CO2.
Impressive as this might be, the world’s forests store thousands of times more CO2 than buildings are ever likely to. Existing forests must be protected to avoid dangerous climate change, a coalition of forest scientists warned in a statement. The world’s forests contain more carbon than exploitable oil, gas and coal deposits, they note.
“Our planet’s future climate is inextricably tied to the future of its forests,” the scientists wrote.
How to prevent timber cities from increasing deforestation
“Protecting forests from unsustainable logging and a wide range of other threats is thus key if timber use was to be substantially increased,” agrees Churkina’s co-author, Christopher Reyer of Potsdam Institute for Climate Impact Research in Germany.
“Our vision for sustainable forest management and governance could indeed improve the situation for forests worldwide as they are valued more,” said Reyer in a statement.
The study used complex simulation modeling to determine that there is enough wood resources available with plantations and the cultivation of fast-growing bamboo by small-scale landowners to construct 90 percent of future buildings out of timber.
Deforestation is almost entirely driven by clearing land for agriculture and for fuel, said Mark Wishnie, global forestry and wood products director at the Nature Conservancy. Very little deforestation globally is for wood products like building material or furniture, according to data from Global Forest Watch, Wishnie said.
“Done right, building future cities out of timber has the potential to cut CO2 emissions and create more forests,” he said in an interview.
Doing it right means managing forests on a landscape scale to ensure they continue to provide habitat for a diversity of species and maintain and clean water flows, among other ecological functions. “To make a significant impact on the climate, timber construction will be needed to be done on a mass scale and there is the potential for large impacts on existing forests,” he said.
Research into the potential impacts of a shift to timber cities is ongoing so that safeguards and appropriate policies can be put in place to protect forests and encourage the use of timber. “These are beautiful buildings with wide open spaces that are wonderful to live or work in.”