The Big Story

Could skyscrapers soon be made of wood?

Could skyscrapers soon be made of wood?

Posting in Architecture | From Issue 11 February 17 & 24, 2014

Concrete's large carbon footprint and the expected rise in urban populations have architects looking for sustainable alternatives to steel and concrete.

In the world of skyscraper men, Bill Baker is the dean of the “supertalls.”

Baker, a man who favors sleek black suits and nerdy round spectacles, specializes in vertigo-inducing towers of steel and concrete that exceed 1,000 feet (that’s 90 stories to you elevator jockeys) and that are often found in oil-rich kingdoms or with names like Trump on them. As chief structural engineer at Skidmore, Owings & Merrill, the famed Chicago architecture firm, Baker is the brains behind dozens of landmarks: the pincer-like 1,824-foot Lotte World Tower in Seoul; the 1,361-foot Trump International Hotel and Tower in Chicago; and his masterstroke, the Burj Khalifa in Dubai. At 2,683 feet (that’s 247 stories, or half a mile high) it is the tallest structure ever built by man.

But on a recent afternoon, in his airy Chicago office, Baker was busy talking up something of a runt: a 42-story residential building that currently has no address, no one to build it, and is only a paper dream of his and his creative staff. That’s because, instead of building it out of the usual steel and concrete, Baker wants to build it almost entirely out of wood.

“We have been working on a lot of climatic issues, trying to improve climatic issues through urban planning,” Baker said. “We said, ‘We can do tall buildings, but can we do them with wood as a way to reduce the carbon impact and create something fully new.’”

If you haven’t been up on these things, Baker’s idea — to build an urban structure made of wood — has been gaining momentum for a few years. Architects looking for an eco-friendly alternative to steel and concrete have been building small apartment towers made of wood. But they haven’t been really tall. The highest in the world topped out at 10 floors in January, with Melbourne’s Forte Development in Victoria Harbour. It only modestly eclipsed the 2009 world record-holder: the nine-floor Stadthaus in London. Both are important successes and both were built with a new class of extra-strong fabricated wood called cross-laminated timber. But they haven’t reached a critical mass, the 40-plus stories that would cover 90 percent of all residential urban habitats. And they haven’t been brought to market by a well-known powerhouse like Baker and SOM.

“Up to now, these buildings have reached eight or nine stories. And while that’s good, it doesn’t change a city, where high-rises around the world rule and are increasingly where urban dwellers live,” said Richard Tomlinson, a managing partner at SOM who oversees strategy. “We haven’t even built one and it’s already a game changer out there.”

In May 2013, the firm released a trailblazing study — the Timber Tower Research Project. It proved, through engineering and mathematics, that you could build a high-rise made of wood that would reduce its carbon footprint and create a sustainable alternative for a booming urban market. Rather than using steel and concrete, which release loads of greenhouse gasses into the atmosphere during production, you use wood, which absorbs carbon while it grows. But not just any wood. You use laminated wood composites like glulam and cross-laminated timber. These are solid panels, similar to plywood in look, engineered for strength through layers of lamination. They are large and dense and more stable than traditional timber. The smaller wood buildings in Melbourne and London use these as well. But SOM’s innovation is to deploy them in a unique way, by cantilevering each floor off of a main trunk, or core, that runs 42 stories up the center of the building. 

“We didn’t want this to be about shape and design, which is why you’ll see that the report doesn’t use any skin on the building,” said Baker, who oversaw the project. “It’s all about the structural system that’s underneath the skin.”

Baker’s team based its study on one of its own groundbreaking buildings — the 1966 Dewitt-Chestnut apartments in Chicago, which pioneered the tree-trunk construction, with steel at its core and reinforced concrete slabs for its floors. It is the same structural system they later used on Chicago’s Sears Tower and the new One World Trade Center.

Will woodscrapers work?

The Timber Tower calls for cross-laminated timber slabs for the trunk, floors and walls, but it will use concrete beams on each floor to offset the floor’s deflection (the point at which it naturally begins to bend). It will also use a two-floor concrete base, making the final tower 70 percent wood. “In some ways, it’s about using the right wood in the right spots,” Baker said, “which is something we’re just getting our heads around.”

Cross-laminated timber is engineered for strength by stacking panels at right angles and bonding them together. They can be as strong as concrete in some cases. It can be made with high-quality finishes, pre-fabricated with window and door cutouts at the factory, and, of particular concern, can reportedly withstand fire. Rather than burning, laminated timber will char quickly in a fire, preventing the wood underneath from igniting. “The analogy we use,” Baker said, “is that it’s hard to start a camp fire with one log. Heat radiates from one log to another. Charring is like kicking a burning log out of the fire.”

But the use of massive amounts of wood in skyscrapers — or what are being called “woodscrapers” — raises an inevitable environmental concern: if it becomes widespread, won’t it devastate forests? The folks at SOM say no. Because the laminated-wood panels are engineered, they don’t need to come from trees in old-growth forests. They can come from smaller species, with smaller trunks, in agriculturally managed forests and even from the millions of fir trees killed by beetle infestation each year in North America.

As with many green-minded efforts — whether putting solar panels on your home or driving an electric car —laminated wood costs more than steel and concrete. However, it allows for saving during the construction process. For instance, the Stadthaus architects conducted a case study that found a similar nine-story building would take 72 weeks to build compared with 49 weeks for the one built with the lighter timber. Builders also used a cheaper mobile crane rather than a tower crane used in a typical concrete structure.

Like other materials, laminated wood can be shipped across continents and oceans. But that, said SOM’s Brian Lee, would erase the carbon-reducing benefits. “You’d want to look and see if you are using within a 500-mile limit, like you might do with LEED guidelines,” for green buildings, Lee said. “This type of building will have more legs in places where you are able to be closer to sustainable forests, not just shipping it halfway around the world.”

It is estimated that some 5 percent of all global greenhouse gas, or carbon dioxide, emissions come from making and transporting concrete, a material that fueled post-war boom years construction. That’s more than the airline industry generates. With 2 billion more people expected to inhabit cities — where tall buildings are jammed together for more housing — in the next 20 years, mass timber high-rises could help offset billions of pounds of greenhouse gases.

According to an estimate by Vancouver architect Michael Green, who designed an eight-story wood building in Prince George that will be the tallest in North America when it’s completed this year, a 30-floor wood laminate building could store 300 metric tons of carbon dioxide. That’s the same amount of gas given off by 118 cars in just a single year of driving.

'Qualities of home and hearth'

Much of the technological innovation and interest in sustainability is coming from an unlikely quarter: the timber industry. SOM’s Timber Tower Report was funded by the Softwood Lumber Board, a trade group based in forest-rich British Columbia that looks to promote and expand its market. The Prince George tower will be a monument to wood in its own backyard. Architects like Green and the guys at SOM say qualities of wood, like its natural warmth, flexibility and connection to nature, are key features for design.

“It’s more relatable to human sensibilities,” Lee said. “People respond to it in a way that has to do with the qualities of home and hearth and the sense of authenticity.”

Laminated-wood floors and walls, for instance, can be exposed, stained to bring out its natural colors. And because it is pliable, it can be warped to create dramatic curves in either the interior or exterior walls of the building, creating a niche market for developers.

“If it gives you a different look and it’s cost effective, then people will build it,” said Ed Woodbury, president of McCaffrey Interests, a Chicago developer that is turning a 500-acre industrial site on Lake Michigan into a new residential and retail community. “There are all these great old heavy-timber buildings in New York and Chicago and Philly, and those are cool buildings. But not everyone can live in one of those. This will deliver a different product that could satisfy people looking for that sort of authenticity.”

The biggest hurdle going forward will be regulatory. Whoever decides to build a 42-story woodscraper (no one has yet stepped forward, though Woodbury said one would fit in with the Lakeshore project) will have to convince local officials to drastically change their building codes. “Building codes in the U.S. only allow for wood structures up to about 45 feet” or about four stories, said SOM's Baker. But SOM is no stranger to convincing regulators to change codes to suit their innovations. They did it, in fact, with their landmark Chestnut building and its unique trunk-and-cantilever structural system.

“Once a developer steps forward and says, ‘OK, let’s do this,’ that’s going to jump start a lot more interest,” said SOM’s Tomlinson. “There’s no better way of getting something validated than to have a real project in the works. People are intrigued and open minded about getting over the technical hurdles. But we want to see the real thing.”

Photo: Flickr/Karen and Brad Emerson

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Kevin Gray

Contributing Writer

Kevin Gray is a freelance writer based in New York. His work has appeared in The New York Times Magazine, New York, The Washington Post, Newsweek, Details and Men's Journal. Disclosure