Wooden skyscrapers are an ambitious and innovative solution to the problems posed by urbanisation. Not only are they faster to build, they have smaller carbon footprints than high-rises made of concrete and steel. <br /><br />Click here to subscribe to The Economist on YouTube: http://econ.st/2GCblkl <br /><br />By 2050 the world’s population is expected to soar to almost 10 billion people and two-thirds of us will live in cities. <br /><br />Space will be at a premium.<br /><br />High-rise offers a solution. But concrete and steel – the materials we currently use to build high – have a large carbon footprint. <br /><br />An answer might lie in a natural material we’ve used for millennia.<br /><br />Throughout history buildings have been made of wood. <br /><br />But it has one major drawback. It acts as kindling. <br /><br />Fire destroyed large swathes of some of the world’s great cities.<br /><br />But by the early twentieth century, the era of modern steelmaking had arrived. <br /><br />Steel was strong, could be moulded into any shape and used to reinforce concrete. It allowed architects to build higher than ever before.<br /><br />So why, after more than a century of concrete and steel, are some architects proposing a return to wood?<br /><br />Concrete and steel are costly to produce and heavy to transport. <br /><br />Wood however can be grown sustainably and it’s lighter than concrete.<br /><br />And crucially, as trees grow, they absorb carbon dioxide from the air, locking it into the timber.<br /><br />One study showed that using wood to construct a 125-metre skyscraper could reduce a building’s carbon footprint by up to 75%<br /><br />Regular timber isn’t malleable like steel or concrete, and isn’t strong enough to build high. <br /><br />But engineers have come up with a solution. It’s called cross-laminated timber, or CLT for short.<br /> <br /><br />CLT is light and it’s comparable in strength to concrete and steel. <br /><br />But how does it cope when burnt with a high heat source? <br /><br />London architects Waugh Thistleton are already designing buildings with this new kind of timber. <br /><br />Andrew and his colleagues designed Britain’s first high-rise wooden apartment block and have recently completed the world’s largest timber-based building.<br /><br />Behind these bricks is a timber core, made from more than 2000 trees, sourced from sustainable forests.<br /><br />And this London practice is not alone in advocating the use of CLT.<br /><br />Ambitious wooden high-rise buildings are also being constructed in Scandinavia, central Europe and North America.<br /><br />As yet, nobody has used CLT to build beyond 55 metres. <br /><br />But Michael Ramage’s research centre in Cambridge, working with another London practice, has proposed a concept design of a 300-metre tower, that could be built on top of one of London’s most iconic concrete structures – the Barbican.<br /><br />Making that jump in height will be a difficult sell.<br /><br />The cost of building wooden skyscrapers is largely unknown, but those costs could be reduced by prefabricating large sections of buildings in factories.<br /> <br />And city-dwellers will need to be persuaded that CLT does not burn like ordinary wood. <br /><br />As an attractive, natural material, wood is already popular for use in low buildings. <br /><br />If planners approve, it could rise to new heights.<br /><br />Daily Watch: mind-stretching short films throughout the working week.<br /><br />For more from Economist Films visit: http://econ.st/2GCbm7T <br />Check out The Economist’s full video catalogue: http://econ.st/20IehQk <br />Like The Economist on Facebook: http://econ.st/2GCbnIZ <br />Follow The Economist on Twitter: http://econ.st/2GAXgUa <br />Follow us on Instagram: http://econ.st/2GAXhrc <br />Follow us on LINE: http://econ.st/1WXkOo6 <br />Follow us on Medium: http://econ.st/2GAXivg
