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  • By 2050, the world's population is expected to soar to almost 10 billion people, and two-thirds of us will live in cities.

  • Space will be at a premium.

  • High-rise offers a solution, but concrete and steel, the materials we currently use to build high, have a large carbon footprint.

  • An answer might lie in a natural material we've used for millennia.

  • Our view is that all buildings should be made of timber.

  • We think that we should be looking at concrete and steel like we look at petrol and diesel.

  • I think it's very realistic to think that someone will build a wooden skyscraper in the coming years.

  • There's a lot of potential that's unrealized for using timber at a very large scale.

  • Throughout history, buildings have been made of wood.

  • But it has one major drawback: It acts as kindling.

  • Fire has destroyed large swathes of some of the world's great cities.

  • But by the early twentieth century, the era of modern steelmaking had arrived.

  • Steel was strong; could be molded into any shape and used to reinforce concrete.

  • It allowed architects to build higher than ever before.

  • So, why, after more than a century of concrete and steel, are some architects proposing a return to wood?

  • If concrete were to arrive as a new material on "Dragon's Den",

  • if you were to pitch it and then say, "I've got this brand-new material; it's liquid, and you can pour it into any shape and it'll solidify."

  • That sounds great.

  • But then, when you say, "We need a whole new fleet of trucks to move it around."

  • "And actually, when it solidifies, it's not strong enough; we have to stick this other stuff in it, called steel."

  • I don't think it would be a compelling case.

  • Concrete and steel are costly to produce and heavy to transport.

  • Wood, however, can be grown sustainably, and it's lighter than concrete.

  • And crucially, as trees grow, they absorb carbon dioxide from the air, locking it into the timber.

  • One study showed that using wood to construct a 125-meter skyscraper could reduce the building's carbon footprint by up to 75%.

  • Regular timber isn't malleable like steel or concrete, and it isn't strong enough to build high.

  • But engineers have come up with a solution: It's called cross-laminated timber, or CLT, for short.

  • It's basically a new material, even though the underlying material is something we've used for millennia.

  • It's cross-laminated, so the layers of wood are glued at 90 degrees to each other.

  • And that makes for a very, very stable material.

  • CLT is light, and it's comparable in strength to concrete and steel, but how does it cope when burnt with a high heat source?

  • Charred wood is extremely insulating; that's the tree's natural protection against a forest fire.

  • It chars, it loses some of its structural mass, but when you remove the source of flame, it extinguishes itself.

  • When steel gets hot, it gets a bit softer.

  • We've actually seen some steel roofs collapse in fires where wooden roofs have not.

  • London architects Waugh Thistleton are already designing buildings with this new kind of timber.

  • There's a CLT building behind, where the timber building sits behind timber clad, and then there's a really simple galvanized steel walkway.

  • Cross-laminated timber is a material we work with a lot.

  • Once these panels arrive on site, we're building, you know, a floor a week, at least.

  • So, this is incredibly fast; this is maybe twice as fast as concrete.

  • Because when you build a concrete buildingwhat we call concrete buildings are actually floor slabs and columns.

  • When we build a cross-laminated timber building, it's building floor slabs, all the external walls, all the internal walls, the lift cores, the stairs, the stair cores

  • everything is made of timber, so these are like honeycomb structures.

  • Andrew and his colleagues designed Britain's first high-rise wooden apartment block, and have recently completed the world's largest timber-based building.

  • Behind these bricks is a timber core made from more than 2,000 trees, sourced from sustainable forests.

  • And this London practice is not alone in advocating the use of CLT.

  • Ambitious wooden high-rise buildings are also being constructed in Scandinavia, central Europe, and North America.

  • As yet, nobody has used CLT to build beyond 55 meters.

  • But Michael Ramage's research center in Cambridge working with another London practice has proposed a concept design of a 300-meter tower,

  • to be built on top of one of London's most iconic concrete structures, the Barbican.

  • The way we've engineered the Oakwood Tower is to look at the global structure.

  • And is it stable, and would it stand up?

  • We believe the answer is yes.

  • The columns at the base of the Oakwood Tower would be about 2.5 meters square, so that's solid timber made of small elements glued together.

  • I think we'll probably see incremental increases from the current height of about 50 meters.

  • And, at some point, someone will make a step change, probably to about 100 meters.

  • Making that jump in height will be a difficult sell.

  • The cost of building wooden skyscrapers is largely unknown, but those costs could be reduced by prefabricating large sections of buildings in factories.

  • And city-dwellers will need to be persuaded that CLT does not burn like ordinary wood.

  • As an attractive, natural material, wood is already popular for use in low buildings.

  • If planners approve, it could rise to new heights.

By 2050, the world's population is expected to soar to almost 10 billion people, and two-thirds of us will live in cities.

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Wooden skyscrapers could be the future for cities | The Economist

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    Rachel Kung posted on 2018/02/07
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