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.
Fuente:economist.com
July 2013
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 the world’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 planning 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.