Has the wooden skyscraper revolution arrived?

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Written by Oscar Holland, CNN

Surrounded by farmland and with a population of under 10,000 people, the Norwegian town of Brumunddal might seem like an unlikely setting for a record-breaking high-rise.

But soaring above the neighboring Mjøsa lake, more than 100 kilometers north of Oslo, the 280-foot-tall Mjøstårnet tower became the world’s tallest timber building when it opened last year.

The 18-story structure contains apartments, office space and the aptly-named Wood Hotel. And beyond putting a small town on the world map, it has added to a growing body of evidence that timber can provide a sustainable alternative to concrete and steel.

Reaching 280 feet in height, Mjøstårnet became the world’s tallest timber building upon opening last year.
Credit: Voll Arkitekter AS / RicardoFoto

“To get attention, you have to build tall,” said Øystein Elgsaas, a partner at the architecture practice behind the record-breaking tower, Voll Arkitekter, in a video call.

“And when you have the world’s tallest building made of timber, everybody says, ‘Wow, what’s going on in Norway?'”

“People are interested, and that is actually the most important part of this building — to showcase that it is possible, and to inspire others to do the same.”

The record-breaking feat was realized thanks to a type of engineered wood called cross-laminated timber, or CLT. Part of a larger group of materials known as mass timber, it is produced by gluing strips of laminated wood together at 90-degree angles to one another, before they’re compressed into huge beams or panels under extreme pressure.

The resulting wooden towers — sometimes dubbed “plyscrapers” — were once the preserve of conceptual designers. But thanks to changes in building regulations and shifting attitudes towards the material, they are quickly becoming a reality.

The tallest tower of the HoHo Vienna project in Austria reaches up to 276 feet.

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

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

Climate economics

Advocates for mass timber claim that, compared to existing alternatives, these towers are quicker to construct, stronger and, perhaps most surprisingly, safer in the event of a fire. It may, however, be their green credentials that explain wood’s rising popularity in recent years.

The construction and operation of buildings accounts for 40% of the world’s energy consumption, and approximately one-third of greenhouse gas emissions. But while concrete emits a huge amount of carbon, trees instead absorb it throughout their lifetime.
Designed by Acton Ostry Architects, the University of British Columbia's student residence Brock Commons Tallwood House, in Vancouver, stands at 174 feet tall.

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

If those trees are then turned into mass timber, that carbon is “locked in,” or sequestered, rather than returned to the atmosphere when the tree dies. Studies suggest that 1 cubic meter of wood can store more than a ton of carbon dioxide.
The developers of Milwaukee’s Ascent apartment complex, for instance, claim that its use of timber 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 further, then it’s a better solution to use them as a building material,” said Elgsaas, adding that, if buildings are designed with longevity in mind, they could keep the carbon out of the atmosphere for generations. “It prolongs the trees’ lifespans (before they decompose) by maybe 100 or 200 years, if done correctly.”

Counting cost

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

So why the recent surge in interest?

According to architect Michael Green, a longstanding advocate for — and designer of — wooden buildings, there are “a whole bunch of things converging right now.” But since his 2013 Ted talk, in which he predicted a coming “revolution” in timber construction, there has been one especially significant shift: cost.
A digital visualization of a 35-story prototype timber building, Proto-Model X, developed by Michael Green Architecture and Sidewalk Labs.

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

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

“There’s more knowledge in the marketplace, more competition, more supply chains … At the time of my Ted talk there was no real infrastructure,” Green said over the phone. “Incrementally, as were seeing more competition, the cost is coming down.”

Price had always been “a barrier,” Green said. Take SHoP Architects’ 10-story design, which won a government competition to occupy a site in New York’s Chelsea district, only to be dropped due to worries over its market feasibility. Or Framework, an ambitious 148-foot-tall timber tower in Portland, Oregon, that was set to be the USA’s tallest wooden tower before was canceled amid cost concerns last year.

However, the cost of cross-laminated timber has fallen in recent years and is now “at par” with traditional materials, Green said. Likewise, Elgsaas reported that the developer behind Norway’s Mjøstårnet tower found the final sum to be “about the same” as a steel and concrete alternative.

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

A prefabricated panel is lifted into place during the construction of Brock Commons Tallwood House in Vancouver. Credit: Acton Ostry Architects/Pollux Chung

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

“If you can make it quicker and open the building quicker, you don’t need to loan the money for as long and can get a return on investment quicker,” said Oldfield, who also authored the 2019 book “The Sustainable Tall Building: A Design Primer, adding: “What we’re finding is driving timber is less the sustainability benefits, and more the benefit to the contractors and clients.”

For Green, the real tipping point will come not when timber is just as cheap — but when it’s cheaper.

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

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

Legal restrictions

Designers like Green are now daring to dream big. Together with Sidewalk Labs, a firm owned by Google parent company Alphabet, the Canadian architect has proposed a “wooden skyscraper city” — consisting of 31 high-rises between 25 and 35 stories tall — that would transform a riverside neighborhood in Toronto.
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 mark its 350th anniversary.
A digital rendering of PLP Architecture's bold proposal for a 984-foot-tall tower in the heart of London.

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

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

The latest update to the International Building Code (IBC), which many countries and US states use as a base model for their own regulations, will allow timber buildings to rise to 18 stories for the first time. The decision is significant given that, before 2018, when Oregon became the first US state to allow 18-story wooden buildings, nowhere in America permitted anything higher than six.

The changes will come into effect in 2021 — though they are only advisory. Some countries, such as Norway, already has looser height restrictions in place, while other countries and US states may opt for tighter building codes than those outlined in the IBC.

And there remains limited data about how large wooden towers will respond, in the long-term, to a variety of risks, from extreme weather to termites and damp.

The most contentious question remains fire risk. The National Association of State Fire Marshals, for instance, opposed the recent update to the International Building Code, citing a lack of requisite fire testing, 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 proper testing and justification” was “premature and would impact the fire suppression environment significantly.”
The concrete industry has also been a vocal critic. According to Build With Strength, a US coalition formed by the National Ready Mixed Concrete Association, cross-laminated timber is “an unproven material that poses major fire risks, especially in high-rise construction.” In addition to concerns about deforestation, the group says sprinklers are ineffective at preventing blazes from spreading through wood buildings. It also cites research suggesting that exposed CLT panels can lead to the “re-flare and re-growth” of fires.

Supporters of mass timber, however, contend that it’s not only safe — it’s actually preferable, as wood burns in a more predictable way.

Studies have also shown that a seven-inch-thick CLT floor has a fire resistance of two hours, which the US Department of Agriculture’s Forest Department says “will address concerns about the fire performance of wood buildings and help take them to new heights.” Steel, on the other hand, is prone to sudden collapse, said Elgsaas. At certain temperatures it can “lose its load-bearing capacity and turn to spaghetti.”
The main tower of the Sara Cultural Centre in Skellefteå, Sweden, will become one of the world's tallest mass timber structures when it opens in 2021.

The main tower of the Sara Cultural Centre in Skellefteå, Sweden, will become one of the world’s tallest mass timber structures when it opens in 2021. Credit: White Arkitekter

Green compares mass timber to a big log placed on a campfire — it doesn’t catch light immediately, and it burns slowly once it does.

“In a big catastrophic fire, generally, if you ask firefighters to go into a heavy timber building versus a steel building, they would much rather go into (the former),” he said. “Because although the beams are charred, they can quickly tell how much char, and therefore how much leftover wood, there is.”

Regulations invariably lag behind technology, Elgsaas added, with each completed tower helping to ease concerns around efficacy and safety.

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

Shifting culture

With shifts in regulation, will come a transformation in cultural attitudes toward wood, Green argues. While a move to timber architecture could represent the most fundamental change in how we construct skyscrapers since the early 20th century, in places with long tradition of wooden buildings, such as northern Europe or North America, it may be less a revolution and more a renaissance.

“We used to build big, giant wood buildings in North America and around the world, but we really stopped when concrete came about,” Green explained, adding that large city fires dampened enthusiasm for the material. In the 1840s, the decade that reinforced concrete was invented, New York, Pittsburgh, St. Louis and Toronto were all devastated by blazes that quickly spread through densely-packed timber-frame buildings.

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

Related video: Japan’s wood-roofed National Stadium opens ahead of Tokyo 2020 Olympics

In hyper-modern cities with little history of building with wood, like Shenzhen or Dubai for instance, there may be limited enthusiasm about its return. Winning developers and architects over, Green argued, should revolve around what he sees as timber’s design advantages.

“Reframing the notions of what modernity is, what forms should be, what makes people more comfortable and what makes the quality of space better, has to be related to human issues — of feeling less stressed, being healthier, being more productive, learning quicker,” he said. “These have to be the defining principles of good design.”

Research has suggested that being in organic environments can have a number of health benefits. A 2010 Austrian study, for instance, found that students in timber classrooms were more relaxed and slept better than those in rooms constructed using traditional materials.

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

“The people living, staying and working there say it feels much cleaner, in a way,” he said.

Challenges ahead

Despite growing enthusiasm for wooden high-rises, long-term environmental challenges remain. For one, if mass timber is to deliver its purported carbon savings, the trees used must be sourced from sustainable forests, said UNSW’s Oldfield.

“If CLT is going to be a major building material for us in the next 30 years, we need to start planting the trees now,” he added. “We looked at how much timber we would need if, by 2050 say, 30% of new buildings were made from CLT — and we’re talking about growing a brand-new forest of 100-by-100-kilometers.

“And there are big questions about whether you should even build forests like that, as they are mono-cultures, whereas 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 addressing: What happens to the sequestered carbon when the building is eventually knocked 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 timber elements and they decompose — or if you burn the building at the end of its life — you leak that carbon dioxide back into the atmosphere,” he said.

Tackling these questions are for the years and decades to come. For now, however, it appears that cost-shy developers are considering the material’s many possibilities. Architect Elgsaas said timber proved itself the best fit for Mjøstårnet — but he keeps an open mind about how the skyscrapers of the future might be built.

“I’m not taking sides — I’m not pro-wood, or pro-concrete,” he said. “I think it’s important that we use the right material for the right job.”

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