When sash window work needs Building Regulations approval, which rules apply, and what changes for listed buildings and conservation areas. This page covers England. Rules in Wales, Scotland and Northern Ireland differ.
Repair or replacement?
Repairing a sash window, such as replacing cords, splicing in new timber or draught-proofing, does not usually need Building Regulations approval. Replacing a whole window, including the frame, is controlled work, so the new window must meet current standards.
How replacement windows are approved
Most homeowners use an installer registered with a competent person scheme, such as FENSA or Certass. The installer self-certifies the work and you receive a certificate, which you will need when you sell the house. If your installer is not registered, the work must be approved by building control before it starts.
The main requirements
- Energy efficiency (Part L): replacement windows in existing homes need to meet a minimum thermal standard, currently a U-value of 1.4 W/m²K or a Window Energy Rating of band B.
- Ventilation (Part F): replacing windows must not make ventilation worse. Trickle or background vents may be needed.
- Fire escape (Part B): where a window is an escape route, the replacement must still open wide enough to escape through.
- Safety glazing (Part K): glass in low-level or other critical locations must be safety glass.
Listed buildings and conservation areas
If your home is listed, you will normally need listed building consent before altering or replacing windows, and doing the work without consent is a criminal offence. Building control can take a flexible approach to energy standards for historic buildings, so the character of the windows is protected. In a conservation area, an Article 4 direction may mean you need planning permission to change windows that face the street. Always check with your local planning authority first.
Get the right paperwork
Ask your installer which scheme they belong to and keep the certificate with your house documents. For listed buildings, choose a specialist with heritage experience who can help with drawings and consent applications. Find a sash window specialist near you.
This page is general guidance, not legal advice. Check current requirements with your local building control or planning authority.