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24, Oct 2017 -

Timber advocates reach for the skies

Timber advocates reach for the skies

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Architects are returning to a building material shunned since the Great Fire of London.

Until the Great Fire of 1666, London was made of wood. Half-timbered structures were crammed in, with the eaves of houses and inns on both sides of the narrow streets almost touching as upper storeys were jettied and bay windows poked out to steal every inch of space.

Wood-framed buildings defined both narrow alleys and the broad streets, which meant flames leapt easily from one building to the next. So, when the city was rebuilt, brick and stone were the chosen materials.

Now timber is back. After more than three centuries, a wooden architecture is once more taking shape in the city, which is leading the world in large-scale urban timber construction.

The harbinger of this trend was Shakespeare’s Globe, the recreation of an Elizabethan theatre that burnt down. Once derided as the fanciful dream of American impresario Sam Wanamaker, the timber theatre on the bank of the Thames was opened in 1997.

Although the Globe was a one-off, it forced architects, engineers and planners to rethink the rules applying to timber building for the modern age. It showed that a substantial public building could be built safely.

The next big step came with the development of cross-laminated timber, or CLT. The huge trees that once populated Britain’s forests are long gone but CLT, a manufactured wood product of timber elements glued together at a perpendicular angle to increase strength, has made large-scale timber structures possible again. Its attractiveness to architects lies in its capacity to act as load-bearing wall, external and internal finish, and insulation all in one.

Anyone walking down Dalston Lane in east London now can see a new 10-storey timber building, billed as the world’s largest CLT structure. Designed by Waugh Thistleton Architects, this is a substantial block of 121 apartments entirely made of timber.

At one-fifth the weight of an equivalent concrete structure, it is lighter on the ground and much lighter on the environment. Because of the ease of construction and off-site fabrication, the number of deliveries to the site during construction has been cut by 80 per cent. However, it is being clad in brick: the market might not ready for wooden real estate that looks like what it is.

A common misconception about timber is that it is more susceptible to fire. In fact, it proves very resistant, by charring rather than going up in flame and resisting collapse for as long as other commonly used structures. It does, however, perform less well acoustically and in spanning widths. The noise question is dealt with by adding extra acoustic layers, but the inability to span the distances needed in larger commercial buildings means CLT is likely to be combined with structural steel, at least in the near future.

Europe’s previous biggest timber building is located nearby in London, overlooking Wenlock Basin. The Cube, by Hawkins Brown Architects, is constructed mostly from CLT, but with a concrete core. Partly clad in brick, it also displays a good expanse of timber.

Even if CLT is cheaper to use, few structural engineers have real experience of building with it, which makes contractors wary of adopting it. However, temporary and experimental buildings are starting to nurture that experience. Last year Alison Brooks Architects built the world’s largest CLT tubular structure at site. The Smile, resembling a wooden banana, was a single, simple curve erected for the London Design Festival. Meanwhile, architects firm dRRM, which has championed CLT for two decades, is working on a concept it calls Wood Blocks. Its proposal is for buildings with warehouse loft-like dwellings that would be entirely timber and “ready to camp in”, with heating and bathrooms, but otherwise fitted out by buyers. Alex de Rijke, dRRM founder, says: “Timber has proved itself, it’s the world’s oldest building material — it’s steel that is the recent upstart.”

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Most dramatic of the recent timber proposals, however, is one by PLP Architecture of an 80-storey timber tower for a site in the City.

The proposal has been developed with the architecture department at Cambridge university, with the intention of provoking a conversation about the possibilities of timber. According to Kevin Flanagan, a partner at PLP, “the proposals were developed as a kind of provocation, to understand what the limits of building in timber in the 21st century might be . . . It could be built using an on-site factory to cut components, perhaps even using robots.”

Just as innovations in steel, glass and concrete revolutionised building in the 19th and 20th centuries, developments in timber construction could lead to new approaches to urban fabrication in the 21st century, says PLP.

Mr De Rijke, however, sounds a note of caution on high-rise proposals. “The timber at the lower levels would have to be so thick the floors would be unoccupiable, so the future certainly is hybrid structures using steel and timber.”

CLT is lighter, faster to build with and greener than steel and concrete. As big cities struggle to meet environmental commitments, they might be keen to encourage the use of renewable timber in construction.

London may no longer be surrounded by the forests of the Elizabethan era, but it is at least at the cutting edge of a new timber architecture.

Source: Financial Times

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