The skyscrapers of the future will be made of wood

By Rima Sabina Aouf

Mic is celebrating Earth Day with an entire week of stories. Over the next few days we’ll be rolling out pieces on hyper-urban farming, the future of construction, the catastrophic environmental costs of the dreaded gender reveal, an optimistic imagining of a meat-free world, and much more. All of the stories will be cataloged here, along with the rest of our environmental coverage.

If architecture in 2021 is any indication, future skyscrapers might have less in common with the Empire State Building than they do with the 1,300-year-old Hōryū-ji temple in Japan. Its five-story pagoda is one of the oldest standing wooden buildings in the world. It is a testament to the durability of our original renewable building material, timber — which, tweaked by contemporary engineering, might be key to slashing the world’s carbon emissions.

The last decade has seen the emergence of “mass timber” — an umbrella term for engineered woods. The most common is cross-laminated timber, or CLT. With mass timber, buildings aren’t made of whole pieces of wood like a log cabin or garden shed. Instead, they’re made of panels, themselves created by gluing strips of wood together in a crisscross pattern that makes them strong enough to compete with concrete or steel.

That strength is crucial. Currently, the construction and operation of buildings accounts for nearly 40% of global carbon dioxide emissions, and concrete alone accounts for as much as 8%. There’s no way of averting the climate crisis without a significant change to how we build tall buildings.

Panels of mass timber form high-rises such as Norway’s 18-story Mjøstårnet, currently the tallest all-timber building in the world. And using hybrid techniques that incorporate some steel and concrete, architects are pushing the material into further heights, with the 25-story Ascent tower underway in Milwaukee and the 40-story Earth Tower proposed for Vancouver. There’s even a 70-story, 350-meter-tall hybrid timber “plyscraper” in the works for Tokyo, although it’s a long way from being realized.

A mock up of a timber building by architecture firm Generate. [John Klein/Generate]

But two recent changes mean that mass timber is no longer reserved for prestige projects in the world’s richest postcodes. The building material is coming to ordinary apartment and office blocks across America, where it can make a real difference. (It’s got a slight head start in Europe.) The first change is that the International Buildings Code, which most U.S. jurisdictions follow, now allows mass timber buildings of up to 18 stories, making building permits easier to get. The second is that with the new Biden administration committed to taking action on climate change in Washington, bills like the CLEAN Future Act should push the construction sector to reduce emissions.

“As it stands now, mass timber is the product to use to achieve net-zero,” says Dalton Ho, the senior sustainable building adviser at Perkins&Will, an architecture firm that frequently works with mass timber. “If you look at a high-performance building that’s as close to zero-carbon as possible, mass timber is kind of the only way you can achieve that right now.”

How mass timber cuts carbon emissions — and even reverses them

The main difference between timber and almost any other building material is that timber acts as a carbon sink, storing the carbon dioxide that trees have absorbed in their lifetime rather than releasing it back into the atmosphere when they die and decompose. Scientists are racing to advance new methods of carbon capture, but trees are currently the only version of the technology that we know how to implement at scale.

But that’s just the beginning. Think of the main material that mass timber displaces — concrete — with its steep CO2 emissions. Those emissions come partly from the chemical reaction of making the key ingredient of cement, partly from the high heats required, and partly out of just how laborious the whole process is. First, a mold for the concrete needs to be constructed on site. Then cement mixers carry and pour the mixture in over a span of weeks. Once the cement mixture is dry, the construction waste from the used mold has to be taken away by more heavy vehicles.

Data showing the warming potential of different building materials. When timber is introduced, the emissions potential steadily decreases. [John Klein/Generate]

With mass timber, that pollution is avoided. Architect John Klein, who researches mass timber at the Massachusetts Institute of Technology and heads his own timber-focused architecture practice, Generate, describes the material as being “like Legos.” The panels are cut to size in factories, they are lightweight and easy to transport, and when they arrive on-site, they can be fit together with simple tools in not much time at all. The eight-story LifeCyle Tower in Austria was constructed in just over a week using prefabricated timber modules…


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