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Technical Frame


NEW HEIGHTS?


The UK’s tallest timber tower, in Hackney, is a hybrid of cross-laminated timber and steel. But are the gains balanced by sustainability trade-offs? Tom Ravenscroft reports


WHEN ARCHITECT HAWKINS\BROWN’S 10-storey 17-21 Wenlock Road residential scheme in the London Borough of Hackney topped out last November, it took the title of the UK’s tallest cross-laminated timber building from a nearby nine-storey residential block by architect Waugh Thistleton on Murray Grove. But unlike its nearby rival, this latest timber tower is not a pure CLT structure. Instead, it’s a hybrid of steel and CLT – a system the architect says allows for greater structural gymnastics, opening up more complex building forms that go “outside the box”. But introducing steel into the mix


naturally adds embodied carbon and dilutes the sustainability credentials of a pure CLT project. Plus, it’s pointed out that the airtightness benefi ts of CLT are dramatically reduced, while adding more materials and trades on site impacts on the programme benefi ts. So are hybrid structures such as


Wenlock Road an evolutionary cul-de-sac 30 | APRIL 2015 | CONSTRUCTION MANAGER


in the search for more sustainable construction methods? Or, for a city that is seeing a boom in high-rise construction, with 117 towers ready to start on site after winning planning in London, do hybrids offer a practical way to sustainably build tall? Hawkins\Brown’s concept design for


Wenlock Road was not initially designed as a timber project. The starting point was its unique form: a cruciform tower, with fl oor plates that twist every two fl oors, designed to achieve as many high- quality fl ats as possible on the site. Its twisted shape allows daylight, ventilation and views into the depth of the plan and means that all 50 residential units benefi t from at least two or three aspects. Aware that Hackney actively


encouraged the use of timber, Hawkins\ Brown mentioned in its design and access statement that it could potentially be developed in CLT. In fact, as the building progressed through the planning process


Main picture and inset: Hawkins\Brown’s Wenlock Road building continues the London Borough of Hackney’s track record for innovating with timber


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