Wooden skyscraper: has the revolution come?

Surrounded by farmland and with a population of less than 10,000 people, the Norwegian city of Brumunddal might seem like an unlikely scenario for an unprecedented high-rise building.

But flying over neighboring Mjøsa lake, more than 100 kilometers (62 miles) north of Oslo, the 280-foot-tall Mjøstårnet tower became the tallest wooden building in the world when it opened last year.

The 18-story structure contains apartments, offices and the aptly named Wood Hotel. And beyond putting a small city on the world map, it has added to mounting evidence that wood can provide a sustainable alternative to concrete and steel.

At 280 feet tall, Mjøstårnet became the tallest wooden building in the world after it opened last year.
Credit: Voll Arkitekter AS / RicardoFoto

“To attract attention, you have to build high,” said Øystein Elgsaas, partner of the architectural practice behind the record tower, Voll Arkitekter, in a video call.

“And when you have the tallest wooden building in the world, everyone says, ‘Wow, what’s going on in Norway?’ “

“People are interested, and that’s really the most important part of this building: showing that it is possible and inspiring others to do the same.”

The record feat was accomplished thanks to a type of engineered wood called cross-laminated wood, or CLT. Part of a larger group of materials known as lumber, it is produced by gluing laminated wood strips together at 90-degree angles to each other, before they are compressed into large beams or panels under extreme pressure.

The resulting wooden towers, sometimes called “pliscrapers,” were once the exclusive property of concept designers. But thanks to changes in building regulations and changing attitudes towards material, they are quickly becoming a reality.

The tallest tower of the HoHo Vienna project in Austria reaches up to 276 feet. Credit: HoHo Vienna / Michael Baumgartner / KiTO

Climate economics

Proponents of massive lumber say that compared to existing options, these towers are faster to build, stronger, and perhaps most surprisingly, safer in the event of fire. However, it may be his green credentials that explain the increasing popularity of wood in recent years.

Designed by Acton Ostry Architects, the University of British Columbia Brock Commons Tallwood House student residence in Vancouver stands 174 feet tall. Credit: Acton Ostry Architects / Michael Elkan

“Trees store carbon, so if you harvest them at the right age when they can’t absorb much more or grow much more, then it’s a better solution to use them as construction material,” said Elgsaas, adding that if buildings are designed Given longevity, they could keep carbon out of the atmosphere for generations. “The life span of trees (before they decompose) is extended by about 100 or 200 years, if done correctly.”

Counting cost

Cross laminated lumber has been used for low-rise buildings in European countries such as Germany and Austria since the 1990s, and the environmental benefits of using lumber have long been known.

So why the recent surge in interest?

A digital visualization of a prototype 35-story wooden building, Proto-Model X, developed by Michael Green Architecture and Sidewalk Labs. Credit: Sidewalk Labs / Michael Green Architecture

As lumber becomes increasingly common, more CLT factories are built and economies of scale reduce prices.

“There is more knowledge in the market, more competition, more supply chains … At the time of my Ted talk there was no real infrastructure,” Green said by phone. “Increasingly, as we saw more competition, the cost is going down.”

However, the cost of cross laminated lumber has decreased in recent years and is now “on par” with traditional materials, Green said. Similarly, Elgsaas reported that the developer behind Norway’s Mjøstårnet tower found that the final sum was “almost the same” as a steel and concrete alternative.

A precast panel is erected during the construction of the Brock Commons Tallwood House in Vancouver. Credit: Acton Ostry / Pollux Chung Architects

But savings can be found in other ways, he said in a phone interview. In particular, the ability to pre-fabricate, or factory-build, wooden components means that other construction costs may drop.

“If you can do it faster and open the building faster, you don’t need to lend money that long and you can get a faster return on investment,” said Oldfield, who also wrote the 2019 book “The Sustainable Tall Building: A design primer, “adding:” What we are finding is that driving wood is less of a benefit to sustainability and more to contractors and customers. “

For Green, the true turning point will not come when wood is just as cheap, but when it is cheaper.

“We are not at the point where (wood is) cheapest,” he said. “And we want it to be cheaper because, at the end of the day, that is what governs the entire industry: the cheapest solution.”

“We have to solve climate change by making things more affordable, not asking people to absorb it and pay more, because it doesn’t work.”

Legal restrictions

A digital representation of PLP Architecture’s bold proposal for a 984-foot-tall tower in the heart of London. Credit: PLP architecture

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But although these architects clearly believe in the structural potential of mass lumber, there remain very practical barriers to the realization of such projects: building regulations.

The changes will take effect in 2021, although they are only advisors. Some countries, such as Norway, already have more flexible height restrictions, while other countries and states in the USA. USA They may opt for stricter building codes than those described in the IBC.

And there remains limited data on how large wooden towers will respond, over the long term, to a variety of risks, from extreme weather to termites to humidity.

Supporters of mass lumber, however, argue that it is not only safe, but preferable, as the wood burns in a more predictable way.

The main tower of the Sara Cultural Center in Skellefteå, Sweden, will become one of the tallest massive wooden structures in the world when it opens in 2021. Credit: Arkitekter white

Green compares the lumber to a large log set in a campfire: it doesn’t turn on the light right away and it burns slowly once it does.

“In a big catastrophic fire, in general, if you ask firefighters to enter a heavy wood building rather than a steel building, they would rather enter (the first one),” he said. “Because even though the rafters are charred, they can quickly determine how much carbon, and therefore how much wood is left over.”

Regulations invariably lag behind technology, Elgsaas added, with each complete tower helping to alleviate concerns about efficiency and safety.

“The more buildings we see that exceed the limit, the easier it will be to propose new building codes and raise the bar on what’s possible,” he said.

Changing culture

With changes in regulation, there will be a transformation in cultural attitudes toward wood, Green argues. While a shift towards wood architecture could represent the most fundamental change in the way we have built skyscrapers since the early 20th century, in places with a long tradition of wooden buildings, such as Northern Europe or North America, It may be less of a revolution and more of a rebirth.

“We used to build huge, giant wooden buildings in North America and around the world, but we really stopped when the concrete was produced,” Green said, adding that the city’s big fires dampened enthusiasm for the material. In the 1840s, the decade when reinforced concrete was invented, New York, Pittsburgh, St. Louis, and Toronto were devastated by flames that quickly spread through densely packed wooden buildings.

“There were some big city fires, and naturally we said, ‘Well, let’s not build anymore with combustible materials’ (…) We knew we could build these big buildings, but we just stopped talking about it.”

In hypermodern cities with little history of wood construction, such as Shenzhen or Dubai, for example, there may be limited enthusiasm about their return. Green argued that the winning developers and architects should revolve around what he sees as wood design advantages.

“Reframing the notions of what modernity is, what forms it should be, what makes people feel more comfortable and what improves the quality of space, has to be related to human problems: feeling less stressed, being healthier, being more productive, learn faster, “he said. “These should be the defining principles of good design.”

Elgsaas also attests to the psychological benefits of wood. He describes the exposed wooden columns of Mjøstårnet, with their organic appearance and different grain patterns, as possessing a certain character that uniform concrete simply cannot achieve.

“People who live, stay and work there say it feels a lot cleaner, in a way,” he said.

Challenges ahead

Despite the growing enthusiasm for wooden skyscrapers, long-term environmental challenges persist. For one thing, if lumber is to provide its supposed carbon savings, the trees used must come from sustainable forests, UNSW’s Oldfield said.

“If CLT is going to be an important building material for us in the next 30 years, we must start planting the trees now,” he added. “We looked at how much wood we would need if, by 2050, 30% of new buildings were made from CLT, and we are talking about cultivating an entirely new forest 100 by 100 kilometers.”

“And there are big questions about whether even forests should be built like this, since they are monoculture, while natural forests have biodiversity.”

Japanese company Sumitomo Forestry plans to spend 600 billion yen ($ 5.6 billion) to build a 1,148-foot-tall wooden skyscraper in 2041 to mark its 350th anniversary. Credit: Sumitomo Forestry Co., Ltd.

Oldfield’s research also raises another long-term question that needs to be addressed: what happens to the sequestered carbon when the building finally breaks down, even if it’s decades or centuries later? And does this negate the benefits of using the material in the first place?

“If you bury the wooden elements and they decompose, or if you burn the building at the end of its useful life, carbon dioxide escapes into the atmosphere,” he said.

Addressing these questions is for years to come. For now, though, it seems like low-cost developers are considering the material’s many possibilities. Architect Elgsaas said wood proved to be the best option for Mjøstårnet, but he keeps an open mind on how the skyscrapers of the future could be built.

“I am not taking sides, I am not in favor of wood or concrete,” he said. “I think it is important that we use the right material for the right job.”

This article was updated with details of the Sidewalk Labs project in Toronto.