July 4th, 2013

Original Source: TheEconomist

WHEN a little-known Canadian architect suggested last year that a skyscraper could be made almost entirely from wood, the head of wood engineering at one of Britain’s biggest builders scoffed. When the architects responsible for the world’s tallest building touted a similar “plyscraper” in May, the idea became harder to dismiss.

Skidmore, Owings & Merrill (SOM) has designed dozens of iconic skyscrapers, including the Willis (formerly Sears) Tower in Chicago, the new World Trade Centre in New York and the current record holder, the 830-metre Burj Khalifa in Dubai. All are made primarily from steel and concrete, the materials of choice for tall buildings for over a century. In its recent Timber Tower research project, however, SOM explored the possibility of recreating a 125-metre-tall reinforced concrete residential building in Chicago using a combination of timber columns, wooden panels and concrete beams and joints.

That the project concluded it was technically feasible, economically competitive with traditional building methods, and could reduce the building’s carbon footprint by up to 75% came as little surprise to Michael Green. The Canadian architect who kick-started the “tall wood” concept in 2012 is currently overseeing the construction of North America’s tallest wooden building in northern British Columbia. Expected to be completed next summer, when it will stand at a relatively modest 30 metres, it is a showcase for Canada’s wood products and building expertise.

The case for wooden high rises is rooted in their environmental benefits. While concrete emits nearly its own weight in carbon dioxide during production, the raw material for plyscrapers literally grows on trees, absorbing carbon from the atmosphere as it does so. Responsibly harvested wood is naturally renewing and, when a building is finally torn down, can be recycled or burned for energy.

Tomorrow’s wooden towers will bear little resemblance to pioneer-style log cabins or the timber-framed McMansions popular across much of America. They rely on engineered wood products called “mass timber” where multiple thin layers of wood are glued or pinned to form solid panels and beams. The production process removes natural variations from the wood, resulting in consistent and interchangeable structural elements. These are then cut to fit in computer-guided mills before being shipped to the building site, dropped into place by crane and bolted together.

Mass timber can be designed to exceed the strength of reinforced concrete and generally resists fire well, charring at its surface instead of catching fire like the planks used in most American homes. The flat-pack nature of its assembly can also dramatically reduce the labour and time required on-site, to the extent that a 25-metre-tall, mostly wooden building was built last year in Austria in just eight days.

Mr Green hopes that his Canadian edifice will not hold the “world’s tallest” title for long. He is making his construction system freely available to other architects and builders under a Creative Commons licence. SOM, although not ready to go fully open-source, has at least not patented the design for its Timber Tower.

But challenges to reaching for the sky remain, especially for the biggest construction market in the West, the United States. There are currently no American manufacturers producing one of the most popular engineered wood products, cross-laminated timber (CLT) panels. This makes it impossible for government-financed building projects, which are obliged to use domestic materials, to make the transition to wood. Moreover, the volumes of wood required might strain sustainable resources. Building the Timber Tower would require the equivalent of 1,700 miles (2,700km) of two foot by four foot (60cm by 120cm) planks. “The lumber industry isn’t organised around delivering this volume of timber to a job site,” says Richard Tomlinson II, SOM’s managing partner.

Yet another drawback is that CLT is unlikely to make an appearance in American building codes until at least 2018. Projects using non-approved products can often still get built, albeit after expensive testing and with liabilities falling on the shoulders of designers, architects and engineers.

None of these issues seems to be preventing some in the construction industry from branching out into wood. SOM is now actively marketing its system to clients and Michael Green is hoping to build a record-breaking 60-metre plyscraper for a university in western Canada. At less than a tenth of the height of the mighty Burj Khalifa, however, wooden skyscrapers still have a long way to grow.

Correction: An earlier version of this article implied that Michael Green is overseeing the construction of the world’s tallest plyscraper. We should have said North America’s tallest. Sorry