Saint-Gobain Weber external wall insulation cuts BISF U-values by 70%

Saint-Gobain Weber external wall insulation system cuts BISF U-value by an Impressive 70% for Cambridge BISF homes

The BISF house is a steel framed house, designed and produced by the British Iron & Steel Federation and erected around the country from 1946. In Cambridgeshire these homes, constructed in 1950, are still lack adequate insulation. This is being remedied with the application of the BBA certified weber.therm XM External Wall Insulation (EWI) system by Saint-Gobain Weber, the leading UK formulator and manufacturer of innovative, high performance materials for the construction industry.

byron square

These BISF homes, owned by Cambridge City Council (CCC),were constructed with a modular steel frame on which the upper storey is clad with corrugated steel sheeting; the lower half of the building is formed with steel reinforced concrete blocks and render. Replacement windows have been installed in past years, fitted within the original steel outer frames which are part of the building framework. Surveys have calculated that the U-value of the properties, which vary slightly due to construction type, are between 0.72 – 0.79 W/m²K.

CCC prioritised the funding of a thermal improvement programme for 20 of the houses around Byron Square, an attractive memorial green space area on the outskirts of the City. The Council has a framework contract in place with main contractor Apollo, based in Essex, for the maintenance and refurbishment of the properties in the Byron Square programme. The Saint-Gobain Weber approved specialist EWI applicator, Sustain Services Limited, of Bury St Edmunds, Suffolk, was brought in to carry out the insulation and render operations. Sustain Services was established as a specialist energy efficiency contractor in 2006 and provides energy reduction and management systems through five divisions: External Wall  installation, housing insulation, commercial insulation, energy efficient M&E systems and a full range of renewables  technologies including solar and heat pumps nationally for RSL, Public Sector and  corporate including Tesco, Asda and M & S.

Saint-Gobain Weber made system calculations for the Cambridge properties with the aim to achieve a U-value as low as 0.23 W/m²K, a massive 70% improvement that will radically reduce energy costs and enhance tenants comfort. For the upper floor steel cladding, 20mm of grey expanded polystyrene (EPS) infills have been fixed between the corrugations to provide a flat surface before a further 80mm of grey EPS is fixed across the panels. On the lower storey, 110mm of grey EPS was installed leveling the wall surfaces at top and bottom which provides a more modern appearance. Insulation is installed around the deep window frames to protect against thermal bridging through the steel.

The weber.therm XM EWI system features a 6mm coat of weber.rend LAC, a low density, polymer modified cement based mortar which acts as an adhesive to bond the insulation onto the original render with additional mechanical fixings. An initial 3mm coat is applied to the surface of the insulation and the reinforcing meshcloth is laid in to the wet mortar. The application of a second coat of render creates the 6mm thick protective skin. When this is dry it is primed with weber PR310 low viscosity primer and coated with weber.plast TF150, an acrylic composite decorative finish, that is applied with a steel float and hawk and finished with a thin plastic float, to deliver a very fine granular textured surface.

Further information about Saint-Gobain Weber’s award-winning and Energy Saving Trust recommended EWI systems and render products is available on 08703 330 070, or 028 9335 2999 in Ireland, or visit and register online for a copy of the Render Solutions Handbook. Alternatively a free download of the new for iPhone and iPad users is available from the iTunes app store.