Replacement windows and Building Regulations: a homeowner’s guide

Replacing a window or an external door counts as controlled work under the Building Regulations in England. Four sets of rules apply, and the job has to be certified. This guide covers each rule, who signs the work off, and when planning permission comes into it.

Part L: energy efficiency

• Windows: a U-value of 1.4 W/m²K or better, or a Window Energy Rating of band B or above
• Doors more than 60% glazed: 1.4 W/m²K or better, or a Door Set Energy Rating (DSER) of band C or above
• Other doors: 1.4 W/m²K or better, or DSER band B or above

These are whole-window and whole-door figures, frame included. Our energy ratings guide explains U-values and WER.

Part F: ventilation

If the windows you are replacing have trickle vents, the new windows must have them too, and the room’s ventilation must be no worse than before.

Where the old windows had none, trickle vents are still worth considering. New windows are far more airtight than the ones they replace. Without some background ventilation, condensation and mould can follow, especially in kitchens, bathrooms and bedrooms.

Part K: safety glass

Glass in critical locations must be safety glass, either toughened or laminated, so it breaks safely if someone falls against it. The critical locations are:

• any glazing within 800 mm of the floor
• glass in a door, and glass within 300 mm of either side of a door, up to 1,500 mm above the floor

This catches more glass than people expect. Low bay windows, side panels beside a front door and the glass in patio and French doors all count. Toughened glass usually carries a small etched mark in one corner.

Part B: means of escape

In a typical two-storey house, bedrooms and other habitable rooms on the first floor need a window suitable for escape in a fire. Some ground-floor rooms do too, depending on the layout. An escape window needs:

• a clear opening of at least 0.33 m²
• at least 450 mm wide and 450 mm high
• the bottom of the opening no more than 1,100 mm above the floor

A replacement must never make an existing escape route worse. Egress (escape) hinges let a casement window open wider and give a bigger clear opening. A tilt and turn window often gives a generous opening too.

Who signs the work off

There are two routes:

1. Competent Person Scheme. An installer registered with a scheme such as FENSA or Certass can self-certify that the work complies. The scheme then sends you a certificate and notifies your local authority.
2. Local authority building control. You or your installer apply to building control before work starts. They inspect the work and issue a completion certificate. There is a fee for this route.

Either way, keep your certificate with your house papers. Your buyer’s solicitor will ask for it when you sell.

Repairs are not controlled work

Replacing a misted sealed unit in an existing frame, a hinge or a lock is a repair, so no certificate is needed. Glass in a critical location should still be replaced with safety glass. See our misted glass and handles and hinges repair pages.

Planning permission

Replacing windows in a house with ones of similar appearance is normally permitted development, so no planning application is needed. You may need permission or consent for:

• flats and maisonettes
• listed buildings, which need listed building consent
• homes in a conservation area covered by an Article 4 direction
• windows that look substantially different from the existing ones

In a leasehold flat the windows may belong to the freeholder, so check your lease and get written consent before you order. If in doubt, ask your council’s planning department first.

Questions to ask before you sign

• Is the installer registered with a Competent Person Scheme for this work? If not, who applies to building control and who pays the fee?
• What are the U-value or WER figures for the windows quoted?
• Which windows will be escape windows, and which will have safety glass?
• Will trickle vents be fitted, and in which rooms?