Wooden skyscraper: has the revolution come?

Wooden skyscraper: has the revolution come?

Written by Oscar Holland, CNN

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.

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

A host of new wooden skyscrapers will open or open in 2020. HoHo Vienna, a mixed-use development just five feet shorter than Mjøstårnet, has just open for business in Austria. And although Europe has traditionally led the charge, North America is catching up fast.
In Vancouver, a city that already houses a 174-foot tall wooden student residence – Pritzker Prize-winning architect Shigeru Ban has designed a “hybrid” condo complex comprising a steel and concrete core with a wooden frame that will open this year. Meanwhile, in Milwaukee, Wisconsin, work on a 238-foot wooden apartment block, Ascent, will begin in June.

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.

The construction and operation of buildings represents 40% of world energy consumption., and about a third of greenhouse gas emissions. But while concrete emits a large amount of carbon, trees absorb it throughout its useful life.
Designed by Acton Ostry Architects, the University of British Columbia Brock Commons Tallwood House student residence in Vancouver stands 174 feet tall.

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

If those trees become mass wood, that carbon is “locked up” or sequestered, rather than returning to the atmosphere when the tree dies. Studies suggest that 1 cubic meter of wood can store more than a ton carbon dioxide.
Developers of the Milwaukee Ascent Apartment Complex, for example, Claim that their use of wood represents the equivalent of taking 2,100 cars off the road.

“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?

According to architect Michael Green, a former defender and designer of wooden buildings, there are “a lot of things converging right now.” But since his 2013 Ted talk, in which he predicted an upcoming “revolution” in wood construction, there has been an especially significant change: cost.
A digital visualization of a prototype 35-story wooden building, Proto-Model X, developed by Michael Green Architecture and Sidewalk Labs.

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.”

Price has always been “a barrier,” Green said. Take the 10-story design from SHoP Architects, which won a government competition to occupy a site in the Chelsea district of New York, only to be abandoned due to concerns about its viability in the market. Or Framework, an ambitious 148-foot-tall wooden tower in Portland, Oregon, which would previously become the tallest wooden tower in the USA. USA cancelled amid cost concerns last year.

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.

Researchers at the University of New South Wales Australia (UNSW) recently completed a 18 month study Comparing a tall wooden building with an equivalent of concrete and steel. According to Philip Oldfield, an associate professor at the university’s built environment faculty, the results showed that the wooden building is still marginally more expensive to produce, in terms of material costs.
A precast panel is erected during the construction of the Brock Commons Tallwood House in Vancouver.

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

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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

Designers like Green now dare to dream big. Along with Sidewalk Labs, a company owned by Google Alphabet’s parent company, the Canadian architect has proposed transforming a waterfront neighborhood in Toronto with around a dozen wooden buildings measuring between 10 and 35 stories high.
Elsewhere, British firm PLP Architecture has created proposals for three wooden skyscrapers, including a 984 foot tall tower In the heart of London. Japanese company Sumitomo Forestry, meanwhile, says it plans to spend 600 billion yen ($ 5.6 billion) to build a 1,148-foot tall wooden skyscraper in 2041 to commemorate its 350th anniversary.
A digital representation of PLP Architecture's bold proposal for a 984-foot-tall tower in the heart of London.

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

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 last update The International Building Code (IBC), which many countries and states in the USA. USA Used as a base model for their own regulations, it will allow wooden buildings to reach 18 stories for the first time. The decision is significant given that, before 2018, when Oregon became the first state of the United States Nowhere in the United States is anything higher than six allowed to allow 18-story wooden buildings.

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.

The most controversial question remains the risk of fire. The National Association of State Fire Marshal, for example, opposed the recent update of the International Building Code, quoting lack of required litmus tests, among other concerns. In a statement, the organization said the changes were the result of “professional judgment” rather than science, adding that allowing larger wooden structures “without adequate evidence and justification” was “premature and would significantly affect the extinction environment fire. “
The concrete industry has also been a vocal critic. According to Build with strength, a coalition of the United States formed by the National Ready Mixed Concrete Association, cross-laminated lumber is “an untested material that poses major fire hazards, especially in high-rise construction.” In addition to concerns about deforestation, the group says sprinklers are not effective in preventing flames from spreading through wooden buildings. Also quote investigation suggesting that exposed CLT panels can lead to “re-inflammation and re-growth” of fires.

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

Studies have also shown that a seven-inch-thick CLT floor has a two-hour fire resistance, which according to the Forest Department of the US Department of Agriculture. USA “It will address concerns about the fire behavior of wooden buildings and help take them to new heights.” Steel, on the other hand, is prone to sudden collapse, Elgsaas said. At certain temperatures it can “lose its carrying capacity and become spaghetti.”
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.

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

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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.”

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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.”

Research has suggested that being in organic settings can have a number of health benefits. A Austrian study 2010For example, they found that students in wooden classrooms were more relaxed and slept better than students in rooms built with traditional materials.

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.

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.

Muhammad

About the author: Muhammad

Wayne Ma is a reporter who covers everything from oil trading to China's biggest conglomerates and technology companies. Originally from Chicago, he is a graduate of New York University's business and economic reporting program.

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