U-values for doors and windows in new housing and refurbishment have been reduced in new guidance for Part L (energy efficiency) of the Building Regulations.

The British Woodworking Federation (BWF) welcomed the changes as tightly defined guidance was “logical in its approach”, but said some window manufacturers would find it challenging to meet reduced U-values without compromising their profit margins.

For the first time, U-values for windows and doors in new dwellings are permitted to be calculated in accordance with BR 443 (conventions for U-value calculations). The area-weighted average U-value required has been reduced to be no worse than 2.0W/m²K.

For existing dwellings where extension/conversion work is undertaken, windows should now have a U-value no worse than 1.6W/m²K (currently 2.0 for replacement windows and 1.8 for windows in extensions). Doors should be 1.8W/m²K or better.

The BWF said it was particularly pleased the Part L update had maintained more than one route to demonstrating compliance – window energy ratings or U-values.

“Offsetting or absorbing any increase in production costs as a consequence of these new regulations is going to be a challenge, although the whole fenestration sector is in the same boat,” added BWF chief executive Richard Lambert.