Existing dwellings in Wales

Existing dwellings in Wales

Part L Wales

On 24th May 2022, the Welsh government issued new and updated Approved Documents in support of the Building Regulations for residential buildings in Wales.  These changes are expected to have a significant impact on glass and glazing products in new and existing dwellings.

Taking effect on 23rd November 2022, the new Approved Document L Volume 1 Dwellings (conservation of fuel and power) includes provisions to improve the energy performance of existing dwellings in Wales.  For replacement windows, doors and rooflights in existing dwellings, the following standards have been set:

Element Standard
Window or roof window
Maximum U value 1.4 W/m2K or minimum Window Energy Rating (WER) band B
Rooflights (horizontal position) Maximum U value 2.2 W/m2K
Doors (>60% internal face glazed)
Maximum U value of 1.4 W/m2K or minimum Doorset Energy Rating (DER) band C
All other doors
Maximum U value of 1.4 W/m2K or Minimum Doorset Energy Rating (DER) band B

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.

There is an alternative approach in the case of dwellings of architectural and historical interest where special considerations apply or there is a need to maintain the character of a façade.  If the windows or doors are unable to achieve the above U values in such dwellings, 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.

For timber windows, a maximum U value of 1.6 W/m2K or Window Energy Rating band C is permissible before 23rd November 2023 to allow manufacturers additional time to transition to full standard of 1.4 W/m2K or WER band B.  For timber doors, a maximum U value of 1.8 W/m2K is permissible before 23rd November 2023 to allow manufacturers additional time to transition to full standard of 1.4 W/m2K.

To satisfy the above requirements, Pilkington provides a range of low-e glass that can provide thermal insulation.

To access the new Approved Documents on the Welsh government's website, please click here.

If you have any questions on Part L 2021 in Wales and what the implications might be for glass, please complete our online contact form, selecting 'Architect' or 'Trade' as the Nature of Enquiry and 'Part L' as the Enquiry Type.

We value your privacy.

We use cookies on this website for analytics, remarketing, social media (optional) and content (essential) purposes.

By clicking ‘Accept All’ you consent to the use of cookies for non-essential functions and the related processing of personal data. Alternatively you can reject non-essential cookies by clicking ‘Essential Only’. You can adjust your preferences at any time by visiting our Cookie Policy and access the settings on that page.

For more information please read our