Render gets in the frame
Thirlestone Homes, part of the Berkeley Homes group, has recently completed two London steel frame developments. One is a Thames-side scheme by architect HM2, part of Harper Mackay. This development is six four-bedroom, four-floor houses arranged around a gated courtyard. The houses have a staircase tower and one double-height window on the front elevations with full-height glazing to the rear elevation overlooking the river and wetlands beyond. Interiors are, says the housebuilder, 'a chic fusion of contemporary minimalism and Art Deco'. The Notting Hill scheme is of five four-storey houses with fashionable curving roofs and, as at Fulham, white rendered walls.
The render is a Weber sbd Expomet system. At the Fulham project, Thirlestone Homes used 80mm thick sheets of mineral wool fixed on to a calcium silicate medium-density sheathing board screwed to the steel frame. The curved towers were insulated with expanded polystyrene board cut to the contour. A 3mm thick Troweltex coating was applied over a reinforcing mesh and two layers of adhesive. At Notting Hill the finish is Trowelcoat, a 1.5mm acrylic coating which allows a drag finish instead of the light granular effect of Tr ow e l t e x .
Thirlestone decided to use Surebuild II steel frame for both developments, not least because Surebuild claims it can have a house up and weather-tight in four days.
Originally an Australian system, Surebuild II is one of the latest steel alternatives to timber frame for houses. Corus Framing in South Wales provides the facility for turning architects' drawings into CAD fabrication drawings and for cutting the steel frame elements needed for the building.
The system is based on 75mm deep galvanized steel C section framing braced at appropriate points. In the fabrication shop steel elements are assembled together into panels using self-piercing rivets, a technique transferred from the automotive industry. Standard floor joists are 150mm deep sigma sections. The design also allows for very flexible plans deploying long-span joists of up to 6m. Sureframe construction is based on the warm frame concept in which insulation is located outside the frame to eliminate cold bridging and surface condensation. Usually, Celotex R insulation is attached to the outside of the frame with fire resisting-plasterboard inside.
The system has the usual BBA and ISO9001 accreditation. Surebuild party walls pass fire tests of one hour for party walls and 30 minutes for floors, and the frame has passed salt spray and sulphur dioxide corrosion tests. U values of brickclad Surebuild walls have U values in excess of projected UK standards and the company's houses routinely achieve SAP ratings of more than 80.