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Technical Frame


>to build a pure CLT building. If you can


stiffen something with steel, use less material and make a more effi cient structure, that makes sense.” As a building material, CLT is becoming


increasingly common in the UK, with its sustainable attributes as the main driver for its uptake. The renewable material, sometimes described as super-plywood, is formed from layers of spruce arranged crosswise and glued to create high- strength panels. On site, there are substantial speed


and cost benefi ts as CLT is a prefabricated material. The wood’s compact layering also provides high levels of airtightness, substantially reducing the amount of energy needed to heat buildings compared to concrete-framed buildings. These advantages were exploited


heavily on the Building Schools for the Future (BSF) programme, with the material being ideally suited for low-rise construction with tight timescales and budgets. (Willmott Dixon’s St Agnes primary in Manchester – based on Eurban’s CLT system – is often cited as the UK’s fi rst “fl at-pack” school). CLT construction


is now established in the education sector: Hawkins\Brown won a 2014 RIBA Award for its exposed CLT project at Hilden Grange prep school in Kent, also designed by project architect Smith. The London Borough of Hackney has in fact become a testbed for housing schemes made of timber, with Waugh


Slotting Wenlock Road together 1


Thistleton’s Murray Grove block the tallest CLT building in the world when completed in 2009. It was followed by Karakusevic Carson Architects’ 41-unit Bridport House in 2011 and now there are numerous CLT housing schemes on site in the borough. So, it is no surprise that Wenlock Road – the latest building to be pushing the boundaries of timber construction – is also to be found in Hackney. Externally, the building is clad in


2 3 5 4


western red cedar, with a dark brick grid used to defi ne the street edge. Internally, because of Part B of the Building Regulations, which state that the building’s structure must retain structural integrity for 90 minutes in the event of fi re, the CLT elements have to be completely covered with fi re-retardant dry-lining. With no visible CLT in the fi nished product and its unusual twisting form, Hawkins\Brown has created a complex design that does not have the look or feel of a standard timber building.


6


1 M&E services 2 Suspended ceiling 3 Internal wall linings 4 Connection to reinforced concrete core 5 Central reinforced concrete core 6 CLT wall panel with pre-cut openings 7 Steel frame braced by inset CLT wall panels 8 Windows, tilt turn 9 Metal balustrades 10 Insulation with drainage runs behind cladding 11 Rainscreen cladding in western red cedar


7 8 9 32 | APRIL 2015 | CONSTRUCTION MANAGER 10 11


Non-typical CLT buildings As Smith says, approvingly, “this is not a CLT-driven form”. In his view, hybrid solutions allow for more non-typical CLT-shaped buildings to be created, maintaining a sustainable agenda while allowing the architects and structural engineers latitude to experiment structurally. “Sustainability should not be a restriction on ambitious design. In the future you will fi nd that there will be more hybrid structures,” he concludes.


Above and below: The high-strength spruce panels play a major structural role, allowing the use of comparatively thin steel columns


“To get the full benefi ts of CLT for mass housing, pure CLT is the only solution” Andrew Waugh, Waugh Thistleton Architects


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