Double glazing regulations

Replacing a window or an external door is building work, so the double glazing regulations in the Building Regulations apply to it. In England, the new window must keep heat in to a set standard, use safety glass where people could fall against it, keep any fire escape route open, and leave the room at least as well ventilated as before. A FENSA or CERTASS registered installer certifies all of this for you.

Double glazing regulations on energy

Replacement windows in England must have a U-value no higher than 1.4 W/m²K, or a Window Energy Rating of band B or better. That is the limit in Approved Document L, and it now applies to timber, aluminium and uPVC alike. Any decent modern double glazed window meets it; single glazing can’t. Our guide to window U-values explains what the numbers mean.

Safety glass in double glazing

Glass that someone could walk or fall into has to be safety glass, which is toughened or laminated. According to the Planning Portal, that covers:

• any glazed panel up to 800mm above the floor;
• any glass in a door up to 1,500mm above the floor;
• side panels within 300mm of a door’s edge, up to 1,500mm.

So low windows, French doors, patio doors and the panels beside a front door all need it. A good quote says which units are toughened.

Fire escape windows

A replacement window must give at least as good a means of escape as the one it replaces. An escape window needs a clear opening of at least 0.33 m², at least 450mm wide and high, with the bottom of the opening no more than 1,100mm above the floor. Upstairs bedrooms are the usual case. Fire-escape hinges, which open the sash fully, help an ordinary casement meet it.

Ventilation

New windows seal far better than old ones. That is good for heat, but bad for damp. The rules expect a replacement to leave the room no worse ventilated than before, so if the old windows had trickle vents, the new ones should too. See window condensation for why this matters.

Doors

The same energy standard applies to replacement external doors. In addition, where a house was built with a level threshold at the main entrance, a new front door has to keep it level, so that wheelchairs and pushchairs still get in.

Who certifies the work

As a result, most homeowners never deal with building control for windows. An installer registered with a competent person scheme such as FENSA or CERTASS self-certifies the job and registers it with the council, and you receive a certificate. Keep it, because your buyer’s solicitor will ask for it when you sell. If your installer isn’t registered, or you fit the windows yourself, you have to apply to building control before the work and pay their fee. See FENSA and CERTASS.

Scotland, Wales and Northern Ireland

These rules are England’s. Wales sets its own Building Regulations, with energy rules that differ from England’s. Scotland works to its own Building Standards and has no FENSA. Northern Ireland has its own regulations, signed off through council building control. In every nation, ask the installer which standard they work to and how they will certify it.

Planning permission is separate

Building Regulations are about how the work is done. Planning permission is about what it looks like, and most replacement windows don’t need it. Read planning permission for windows if you live in a conservation area or a listed building, or are adding a new bay. Then get quotes from registered installers.