Award-winning timber window manufacturer Mumford & Wood is proud to announce a U-value of 1.1 W/m²K for the market-leading Conservation™ box sash. This product is the highest specification window in the comprehensive range of traditional and contemporary-style sash windows, casements, bi-fold, French doorsets and entrance doors and is designed to directly retro-fit in place of original box sash windows in older properties, or to create a traditional appearance in new builds.

Measurements have been tested in accordance with the new British Board of Agrément (BBA) and British Woodworking Federation (BWF) software tool in compliance with BS EN ISO 10077-1:2006. Test criteria is based on a timber density of 500 kg/m³, frame thickness of 160mm and casement thickness of 57mm. Using a 16mm double glazed argon gas filled cavity, low emissivity coated glass and warm edge spacer, the thermal transmittance of 1.1 W/m²K is certificated to BBA-BWF-0261772. The Conservation™ box sash is operated with traditional weights and pulleys and combines enviable period styling and features together with the very latest timber window technology to provide superb thermal and acoustic performance and improved security.

Owen Dare. Technical Director for Mumford & Wood, said "Going forward the company will continue to submit all products in the extensive Conservation™ range for BBA-BWF measurement and compliance results, and with products that achieve exceptional U-values in the new Part L Building Regulations, we are confident that the results will be equally impressive.”