Wooden skyscrapers: Has the revolution come?

Wooden skyscrapers: Has the revolution come?

Written by Oscar Netherlands, CNN

Surrounded by farmland and with a population of less than 10,000, the Norwegian town of Brumunddal may seem an unexpected setting for a record-breaking high rise.

However, the 280-foot-high Mjøstårnet tower, rising above the neighboring Lake Mjøsa, more than 100 kilometers (62 miles) north of Oslo, became the world’s tallest wooden building when it opened last year.

The 18-storey building includes apartments, office space and the appropriately named Wood Hotel. And beyond putting a small town on the world map, he added an increasing evidence that wood can provide a sustainable alternative to concrete and steel.

Reaching a height of 280 meters, Mjøstårnet became the highest wooden structure opened last year.

Reaching a height of 280 meters, Mjøstårnet became the highest wooden structure opened last year.
Credit: Voll Arkitekter AS / RicardoPhoto

“You have to build tall to attract attention,” said Øystein Elgsaas, partner of architectural practice behind the record-breaking tower in the video call.

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

“People are interested and actually the most important part of this building – to show that it’s possible and to inspire others to do the same.”

The record-breaking success was thanks to cross-laminated timber or a kind of treated wood called CLT. Laminated strips of wood, which are part of a larger group of materials known as mass lumber, are produced by gluing them together at 90 degrees angles before being pressed into large beams or panels under extreme pressure.

The resulting wooden towers – sometimes called “plyscrapers” – were once guardians of conceptual designers. However, they quickly become a reality thanks to changes in building regulations and attitudes towards materials.

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

In 2020, a series of new wooden high-rise floors will be broken or opened. Mixed use HoHo Vienna, just five meters shorter than Mjøstårnet opened for business In Austria. While Europe has traditionally led this accusation, North America is growing fast.
In Vancouver – already a city 174 meters tall wooden dormitory – Pritzker Award-winning architect Shigeru Ban, “hybrid” apartment complex It includes a steel-framed steel and concrete core to be opened this year. Meanwhile, working on the 238-meter wooden apartment block Ascent in Milwaukee, Wisconsin will begin in June.

Climate economy

Mass timber advocates claim that these towers are built faster, stronger, and perhaps surprisingly safer in the event of fire, compared to the available options. However, there may be green credentials that explain the growing popularity of wood in recent years.

Construction and operation of buildings 40% of world energy consumptionand about one third of greenhouse gas emissions. But while concrete emits large amounts of carbon, the trees absorb it throughout its lifetime instead.
Designed by Acton Ostry Architects, the University of British Columbia, Vancouver student residence Brock Commons Tallwood House is 174 meters tall.

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

If these trees are then converted into mass timber, this carbon is “locked” or sequestered instead of returning to the atmosphere when the tree dies. Studies show that 1 cubic meter of wood can be stored more than a ton carbon dioxide.
For example, the developers of Milwaukee’s Ascent apartment complex, Allegation indicates that the use of timber is equivalent to taking 2,100 cars off the road.

“Trees store carbon, so if you harvest them at the right age where they can’t absorb or grow more, it’s a better solution to use them as a building material,” Elgsaas said. Designed with longevity in mind, they can keep carbon away from the atmosphere for generations. “If done right, it extends the life of the trees (before separation) maybe 100 or 200 years.”

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Cost calculation

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

So why has interest increased recently?

According to architect Michael Green, a long-time advocate and designer of wooden buildings, “there is a lot going on right now.” But since 2013 Ted talkThere was a particularly important change that predicted an upcoming “revolution” in timber construction: cost.
Digital display of Proto-Model X, a 35-story prototype wooden building developed by Michael Green Architecture and Sidewalk Labs.

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

As mass lumber becomes more and more widespread, more CLT factories are established and economies of scale reduce prices.

“There’s more information, more competition, more supply chains in the market … There was no real infrastructure during my speech,” said Green. “As you see more competition, the cost decreases.”

Green said the price is always “an obstacle”. Get the 10-story design of SHoP Architects, who won a government contest to occupy a site in Chelsea district in New York, but worry on market feasibility. Or Framework, an ambitious 148-meter wooden tower set in Portland, Oregon, previously set as the tallest wooden tower in the USA It is cancelled amid last year’s cost concerns.

However, the cost of cross-laminated timber has dropped in recent years and is now “even” with traditional materials. Similarly, Elgsaas reported that the developer behind the Norwegian Mjøstårnet tower found that the final total was “the same” as the steel and concrete alternative.

Researchers at Australia’s University of New South Wales (UNSW) have recently 18 months of work Comparison of a high wooden building with concrete and steel equivalent. According to Philip Oldfield, an associate professor at the university’s established environmental faculty, the findings showed that the wooden structure remained marginally more expensive in terms of material costs.
A prefabricated panel was removed during the construction of Brock Commons Tallwood House in Vancouver.

A prefabricated panel was removed during the construction of Brock Commons Tallwood House in Vancouver. Credit: Acton Ostry Architects / Pollux Chung

However, he said in the phone call that savings can be found in other ways. In particular, the ability to manufacture wooden parts in a prefab or factory means that other construction costs can be reduced.

“Sustainable High-Rise Building: A Design Primer,” adds: “What we find is timber sustainability, reduced sustainability benefits, and greater benefits for contractors and customers.”

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

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

“We have to solve climate change by making things more economical, we don’t want people to absorb and pay more, because it doesn’t work.”

Legal restrictions

Designers like Green now dare to dream big. Canadian architect with Sidewalk Labs, owned by Google parent company Alphabet, Riverside neighborhood Toronto With a dozen wooden buildings between 10 and 35 floors high.
Elsewhere, the English firm PLP Architecture, for three wooden skyscrapers, 984 foot high tower In the heart of London. Meanwhile, Japanese company Sumitomo Forestry announced that it plans to spend 600 billion yen ($ 5.6 billion) to start a company. 1,148 feet tall wooden skyscraper It celebrated its 350th anniversary in 2041.
A digital representation of PLP Architecture's bold proposal for a 984-foot high tower in central London.

A digital representation of PLP Architecture’s bold proposal for a 984-foot high tower in central London. Credit: PLP Architecture

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However, while these architects clearly believe in the structural potential of mass timber, there are many practical obstacles in the realization of such projects: building arrangements.

Latest update The International Buildings Law (IBC), which is used by many countries and the US states as the basic model for their regulations, will allow the first time to increase the 18th floor of wooden buildings. The verdict is that before Oregon, first US state Nothing higher than six was allowed anywhere in America to allow 18-storey wooden buildings.

The changes will take effect in 2021 – but these are only consulting. Some countries, such as Norway, already have looser height restrictions, while other countries and US countries may prefer stricter building codes than those specified in the IBC.

And there is limited data on how large wooden towers will respond to various risks in the long term, from extreme weather conditions to termites and humidity.

The most controversial question remains the risk of fire. For example, the National State Fire Shalwar Association opposed the latest update to the International Building Code, mention Among other concerns, the lack of necessary fire tests. In a statement, the organization said the changes are the result of “professional judgment” rather than science, and “allowing larger wooden structures” without proper testing and justification is early and will significantly affect the firefighting environment.
The concrete industry has also become a vocal critic. By Build with PowerCross-laminated wood, a US coalition founded by the National Ready-Mixed Concrete Association, is “an unproven material that creates huge fire risks, especially in high-rise construction.” In addition to concerns about deforestation, the group says sprinklers are ineffective in preventing the spread of flames to wooden buildings. Also quotes Research It suggests that exposed CLT panels can lead to “re-flaming and regrowth” of fires.

However, mass lumber supporters claim that this is not only safe, but also preferred because wood burns more predictably.

Work also includes a seven-inch thick CLT floor. two-hour fire resistance“The US Department of Agriculture’s Forest Department will” address concerns about the fire performance of wooden buildings and take them to new heights, “he said. Elgsaas said steel was prone to sudden collapse. At certain temperatures it may “lose its carrying capacity and return to spaghetti”.
The main tower of the Sara Cultural Center in Skellefteå, Sweden, will be one of the longest mass wood structures in the world when it is opened in 2021.

The main tower of the Sara Cultural Center in Skellefteå, Sweden, will be one of the longest mass wood structures in the world when it is opened in 2021. Credit: White Arkitekter

Green compares mass timber with a large log placed in a campfire – it does not shine immediately and burns slowly once.

“In a major disaster fire, they usually prefer to enter (old) earlier if you want firefighters to enter a heavy wooden building against a steel building.” Said. “Although the beams are charred, they can quickly tell how much coal and therefore how much wood is now.”

Elgsaas added that the regulations always lag behind technology and that each completed tower helps reduce concerns about efficiency and safety.

“The more buildings we see when pushing the limit, the easier it will be to suggest new building codes and raise the bar on what is possible,” he said.

Changing culture

Green argues that with changes in regulation, there will be a transformation in cultural attitudes towards wood. While the transition to wooden architecture can represent the most fundamental change in the way we built skyscrapers since the early 20th century, in places with a long tradition of wooden buildings, such as northern Europe or North America, this could be less revolution and more renaissance.

“We would have built huge, massive wooden buildings in North America and the world, but we really stopped when concrete came,” said Green, adding that big city fires have reduced enthusiasm for the material. The decade, reinforced concrete invented in the 1840s, New York, Pittsburgh, St. Louis and Toronto were devastated by flames that quickly spread into densely packed wooden frame buildings.

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

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For example, in hyper-modern cities with little history of wood construction, such as Shenzhen or Dubai, there may be limited enthusiasm for its return. Green should turn around what the winning developers and architects see as design advantages of timber.

“What modernity is, what forms should be, what makes people more comfortable and better the quality of the space should be related to human problems – feeling less stressed, healthier, more productive, faster to learn,” he said. “These should be the defining principles of good design.”

Research has suggested that being in an organic environment can provide various health benefits. one 2010 Austrian studyFor example, they found that students in wooden classrooms slept more comfortably and better than rooms built using traditional materials.

Elgsaas also proves the psychological benefits of wood. Mjøstårnet’s organic appearances and different grain patterns define open wooden columns as having a certain character that uniform concrete cannot achieve.

“People who live, stay and work there say they feel much cleaner in a way.”

The challenges ahead

Despite the growing enthusiasm for high increases in wood, long-term environmental challenges remain. First, if the mass lumber will provide the claimed carbon savings, the trees used must be sourced from sustainable forests, says UNSW’s Oldfield.

“If CLT will be an important building material for us in the next 30 years, now we need to start planting trees.” “We looked at how much timber we would need if 30% of new buildings were built from CLT by 2050 – and we’re talking about growing a brand new forest of 100 x 100 kilometers.

“Also, there are big questions as to whether you can create such forests because natural forests have biodiversity because they are single-cultures.”

Japanese company Sumitomo Forestry plans to spend 600 billion yen ($ 5.6 billion) to build a 1,148 feet high wooden skyscraper to celebrate its 350th anniversary in 2041.

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

Oldfield’s research also raises a long-term question that needs to be addressed: what will happen to the carbon that will eventually be retained when the building collapses, even after thousands or centuries later? And does this eliminate the benefits of using the material in the first place?

“If you bury the timber elements and crumble – or if you burn the building at the end of its life – you will leak this carbon dioxide back into the atmosphere,” he said.

Solving these questions is years and decades. For now, however, shy developers seem to be considering many possibilities of the material. Architect Elgsaas proved that timber is best suited for Mjøstårnet – but said he is open-minded about how to build the skyscrapers of the future.

“I am not taking sides – I am not pro-wood or concrete-pro,” he said. “It is important that we use the right material for the right job.”

This article has been updated with details of the Toronto project of Sidewalk Labs.

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