Do I need planning permission for an extension?
Not always. In England many single-storey rear extensions are permitted development, so no planning application is needed, provided they stay within set size limits: up to 3 m deep on an attached house or 4 m on a detached house, and no higher than 4 m. Larger rear extensions need prior approval, and most two-storey and side extensions need full householder planning permission. Building regulations approval is needed either way.
What are the permitted development limits for extensions in England?
- Single-storey rear: up to 3 m deep (attached house) or 4 m (detached), maximum height 4 m.
- Larger single-storey rear: up to 6 m (attached) or 8 m (detached) through the prior approval process, where neighbours are notified.
- Within 2 m of a boundary, eaves no higher than 3 m.
- Side extensions: single storey, no higher than 4 m, no wider than half the width of the original house.
- Two-storey rear: no more than 3 m deep and at least 7 m from the rear boundary.
- Extensions and outbuildings together cannot cover more than half the land around the original house.
- Materials should be similar in appearance to the existing house.
"Original house" means the house as first built or as it stood on 1 July 1948, so earlier extensions count against the allowance.
When is planning permission always needed?
You need a planning application if you live in a flat or maisonette, if the house is listed, if the original planning permission removed permitted development rights (common on newer estates), if an Article 4 direction applies, or if the extension goes beyond the limits above. In conservation areas, National Parks and National Landscapes, side extensions and two-storey rear extensions are not permitted development.
Should I get a lawful development certificate?
It is optional but sensible. A lawful development certificate from the council confirms that an extension was permitted development, which avoids questions when you sell. We prepare the application as part of the design.
What about Wales, Scotland and Northern Ireland?
Each nation sets its own permitted development rules. Wales has broadly similar small-extension rules to England but no larger-extension prior approval route. Scotland has its own householder rules and requires a building warrant before any work starts. Northern Ireland uses the Planning (General Permitted Development) Order (Northern Ireland) 2015. See our guide to building outside England.
How long does planning permission take?
Councils aim to decide householder applications within eight weeks of the application being validated. Prior approval for a larger rear extension has a 42-day decision period in England.
Related projects
- Single-storey extensions
- Double-storey extensions
- Side return extensions
- Architectural design and planning
This guide is general information about building work in the UK, not legal or tax advice. Rules change, so check the current position for your property with the council, HMRC or a qualified adviser before relying on it.