Permitted development or planning permission?
Many houses have permitted development rights — a set of national limits within which you can extend without a full planning application. If your project goes beyond those limits, you need householder planning permission. Councils aim to decide householder applications within 8 weeks.
The 50% rule
Under permitted development, extensions and outbuildings together must not cover more than half the area of land around the original house — the house as it was first built (or as it stood on 1 July 1948). Previous extensions count, even if a previous owner built them.
When you'll usually need planning permission
- Two-storey and wraparound extensions
- Extensions forward of the front of the house (other than small porches)
- Side extensions in conservation areas or the Chilterns National Landscape
- Anything on a listed building (which also needs listed building consent)
- Flats and maisonettes, which don't have householder permitted development rights
Getting certainty: Lawful Development Certificates
If your project is permitted development, you can apply to the council for a Lawful Development Certificate. It isn't compulsory, but it proves the work was lawful — useful when you sell.
Building regulations are separate
Even without planning permission, almost every extension needs building regulations approval for structure, fire safety, insulation and drainage.
This guide summarises rules for houses in England at the time of writing and is for guidance only. Rules differ for flats, listed buildings and designated land, and can be changed by Article 4 directions. Always check the Planning Portal or ask us — we confirm the route for your home before design starts.