Do I need building regulations for a like-for-like replacement?

Yes. There is no exemption for replacing a window with a similar one. The work is notifiable either way, which is what the competent person schemes exist to handle.

What about repairing rather than replacing?

Repairs such as replacing a failed sealed unit in an existing frame, or refurbishing a sash, are generally not notifiable. Replacing the whole frame is.

What happens if the work does not comply?

The local authority can require it to be put right, and the lack of a certificate will surface when you sell. In practice it usually becomes a price negotiation or an indemnity policy at the point of sale.

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Do I need building regulations approval for new windows?

Yes. Replacing a window or an external door in England and Wales is notifiable building work. In practice a FENSA, CERTASS or Assure registered installer self-certifies it and sends you a certificate, so you do nothing. If your installer is not registered, you have to apply to building control yourself.

People often assume a like-for-like replacement is exempt. It is not, and the certificate is the thing a buyer’s solicitor asks for years later.

What the regulations require of a replacement

A replacement window has to be at least as good as the standard set in Approved Document L. Since the 2021 edition that means a U-value no worse than 1.4 W/m²K, or Window Energy Rating band B. Replacement doors have their own equivalent threshold.

Other parts apply too. Approved Document F covers ventilation, which is why trickle vents now appear on most replacements. Approved Document K covers safety glazing in critical locations, and Approved Document B covers means of escape from habitable rooms.

A window frame seated in a brick opening mid-installation, with packers at the jamb and a spirit level across the frame. — A frame packed and levelled in the opening. A registered installer self-certifies this work against the regulations and sends you the certificate. Illustrative. Not work carried out by TrustedGlazing.

Where people get caught out

Removing an escape window. If the window you are replacing serves as a means of escape, the replacement must too. Reducing the number of openers to save money can quietly break this.
Leaving off trickle vents. An installer offering to omit them is offering to make the work non-compliant on your behalf.
Safety glazing. Glass low to the floor, beside a door or in a door has to be toughened or laminated. This is not optional and not an upgrade.
Enlarging the opening. That is structural work and a separate matter from the window itself.

Scotland and Northern Ireland differ

Scotland operates building warrants through local authority verifiers rather than the competent person schemes used in England and Wales, and the technical standards are set out separately. Northern Ireland has its own building regulations too.

We only match installers in England, so everything on this page is written for England and Wales. If your property is elsewhere, check with your local authority rather than relying on this.

Questions

Do I need building regulations for a like-for-like replacement?: Yes. There is no exemption for replacing a window with a similar one. The work is notifiable either way, which is what the competent person schemes exist to handle.
What about repairing rather than replacing?: Repairs such as replacing a failed sealed unit in an existing frame, or refurbishing a sash, are generally not notifiable. Replacing the whole frame is.
What happens if the work does not comply?: The local authority can require it to be put right, and the lack of a certificate will surface when you sell. In practice it usually becomes a price negotiation or an indemnity policy at the point of sale.

Note This guide is general information about England and Wales, not advice about your specific property. TrustedGlazing is an introducer and does not install, survey or quote. Rely on your installer's survey and your local authority for decisions about your own home.