Existing Dwellings

Existing Dwellings (England)

What is Part L 2021?
Changes to the Building Regulations for existing dwellings in England are expected to have an impact upon glass and glazing products in residential buildings.

Published on 15th December 2021 and coming into force on 15th June 2022, the government has set out its new requirements for Part L (conservation of fuel and power) of the Building Regulations and the supporting Approved Document for existing dwellings in England.

The 2021 edition of Approved Document L Volume 1 has made changes to the standards for fabric performance of building elements in existing dwellings.  For replacement windows, doors and rooflights in existing dwellings, the following standards have been introduced:

Fabric element
Maximum U-value (W/m2K)
Window (including roof window or curtain walling)
1.4 or minimum WER Band B
Doors with greater than 60% on internal face glazed
1.4 or minimum Door Set Energy Rating (DSER) Band C
Other doors
1.4 or minimum Door Set Energy Rating (DSER) Band B

For timber windows, a maximum U-value of 1.6 W/m2K is permissible. For external fire doorsets, a maximum U-value of 1.8 W/m2K is permissible.

WER, Window Energy Rating, is generally considered a better indicator of the energy performance of a window because it considers a range of parameters, including the useful solar heat gain.  The U-value is the total U-value of the window, taking into account both the glass and frame.

The U-value of a rooflight should be based on the outer developed surface area, which is often greater than the area of the roof opening.

The proposals include an alternative if windows or fully glazed external pedestrian doors cannot meet the above requirements because of the need to maintain the character of the building.  In such cases, they should achieve or better a centre pane U value of 1.2 W/m2K or be upgraded to low emissivity (low-e) secondary glazing.

Pilkington manufactures a range of low emissivity glass for thermal insulation that can help windows and doors to achieve low U-values.

The 2021 editions of Approved Document L Volumes 1 and 2 can be downloaded from here.

If you have any questions on the new regulatory requirements and what the implications might be for glass, please complete our online contact form, selecting 'Architect' or 'Trade' as the Enquiry Type and 'Part L' as the Nature of Your Enquiry.