Do Replacement Windows Need Building Regulations?

What the regulations cover

According to the Planning Portal, the main areas that apply to replacement windows and doors are:

• Energy efficiency. New windows and doors have to meet a minimum standard for heat loss.
• Ventilation. Rooms still need enough ventilation once the new windows are in.
• Means of escape. Replacement escape windows must offer at least the same potential for escape as the old ones.
• Safety glazing. Glass in certain low-level areas and in and around doors has to be safety glass.
• Access. On homes built since 1999, the threshold of the main entrance door should stay level.

Energy efficiency

Heat loss through a window is measured as a U-value. The lower the figure, the less heat escapes. In England, Approved Document L sets a limit for replacement windows in existing homes of 1.4 W/m²K, or a Window Energy Rating of band B or better. Replacement doors have a similar limit.

Wales publishes its own version of Approved Document L. The standards for replacement windows are broadly the same, but it is the Welsh document that applies in Wrexham, Chirk, Llangollen and Welshpool.

Ventilation, escape and safety glass

Ventilation

Modern windows are much more airtight than old ones. If the windows you are replacing had trickle vents, the new ones should not leave the room with less ventilation than before. Kitchens and bathrooms usually rely on extractor fans as well.

Means of escape

The Planning Portal sets out the size of an escape window: an openable area of at least 0.33 square metres, at least 450mm high and 450mm wide, with the bottom of the opening no more than 1100mm above the floor. This mainly matters for upstairs bedrooms.

Safety glazing

Safety glass is needed in critical areas, such as glazing within 800mm of the floor, glass in doors up to 1500mm from the floor, and side panels close to a door.

How the work gets signed off

There are two ways to show replacement windows comply:

• The installer is registered with a competent person scheme, such as FENSA or CERTASS. They self-certify the work, the scheme notifies the council, and you receive a certificate.
• If the installer is not registered, the work has to be approved by building control through the council or a registered building control approver, who will inspect and issue a completion certificate.

The Welsh Government lists the competent person schemes that apply in Wales for replacement windows and doors. Either way, ask who is responsible for the sign-off before work starts, and keep the certificate with your house documents. Solicitors often ask for it when you sell.

Do you need planning permission?

Usually not, if the new windows are similar in appearance to the old ones. The exceptions are the same as for most home improvements: listed buildings, flats, conservation areas, and homes where permitted development rights have been removed. If any of these apply, check with Shropshire Council, Wrexham County Borough Council or Powys County Council before ordering.

Questions to ask before you order

• How will the work be signed off, and will I get a certificate?
• Do the new windows meet the U-value or energy rating limit?
• Will the bedroom windows still work as escape windows?
• Where will trickle vents go, if they are needed?
• Is safety glass included where it is required?

If you are still deciding whether your windows need replacing at all, read our guide to the signs your windows need replacing.