The British Fenestration Rating Council (BFRC) is an independent, government-backed initiative set up to enhance the energy performance of buildings. BFRC in conjunction with the UK glazing industry and European partners has developed a Window Energy Rating to assess the energy performance of domestic windows.

The BFRC Rating for windows is now included in the Building Regulation Part L with effect from April 2006. Beside the existing target U-Values for replacement windows, compliance to Part L can be shown using certain Window Energy Ratings.

The standard for replacement windows in an existing dwelling should be an energy rating of 'E' or better and the standard for new windows in extensions should be a 'D' Rating or better. For new dwellings the compliance with Part L is proven via a Target CO² Emission Rate, which needs to be met, without specific BFRC requirements for the windows.