Replacement Windows and Building Regulations – what you need to know

When replacing any part of your home, building regulations and planning permission are the primary factors you’ll need to bear in mind. The rest of this page is designed to equip you with all the information you need on building regulations for replacement windows within the home.

Building regulations for replacement glazing

All replacement glazing has been covered by building regulations since April 2002, with areas covered including safety, air supply and thermal performance. Here are the key points:

Heat loss. All windows and doors must comply with the requirements of the building regulations, with the relevant U-values, which can be found here.
Safety glazing. Any glass in a critical area must be equipped with safety glazing. Critical areas are regarded as:

• Any glazed area within a window below 800mm from floor level
• Any glazed area within a window with is less than 300mm from a door and up to 1500mm from floor level
• Any glazed door up to 1500mm from floor level


There are rules in place that apply to ventilation, with the type and extent of it depending on the use and size of the room. Rooms that regularly produce steam, for example, will require higher levels of ventilation (mechanical fans or windows) whereas standard rooms with regular windows will usually be unaffected.

Fire Safety

Fire safety consists of two main issues: fire spread through ‘unprotected areas’ and the means of escape in the event of a fire.

• External doors and windows will often need to have fire resistance and depending on their proximity to the property boundary may need to have specified fire resistance as part of the specification.
• Means of escape requires windows to have openings large enough to provide some potential for exiting in the case of an emergency – or at least the same amount as the old windows they’re replacing. Again, it’s essential to check this with the relevant authorities.

Do I need planning permission too?

For a lot of windows, planning permission isn’t necessary. It won’t be required if you’re:

• Carrying out repairs, maintenance or minor improvements (such as repainting the frames)
• Inserting new windows or doors that are similar in appearance to the construction of your home (a bay window, for instance, would NOT be permitted, and would require permission).

If the new windows are in an upper-floor side elevation, they must be obscure-glazed and non-opening or more than 1.7 metres above the floor level.

The one thing to consider is that in some areas, local councils may withdraw permitted development rights under an Article 4 Direction. This will typically be the case in listed buildings, but can also occur elsewhere – it may be worth double checking with your local council before proceeding with the works, just in case.

We’ve also got a guide to planning permission for replacement glazing here which could provide you with more useful information.

Give us a call

If you’re at all unsure about how building regulations will affect your new windows or doors, then give us a call today on 01284 764045. We have years of experience in the industry, and will happily help you manage your new project.