Do I need planning permission for an extension?
Many single-storey extensions do not need a planning application because they fall within permitted development. In England that usually means a rear extension of up to 3 m (4 m on a detached house), or 6 m and 8 m through prior approval. Two-storey side extensions, most wraparounds and anything on designated land normally need planning permission.
What is permitted development?
Permitted development rights let you extend a house without applying for planning permission, as long as the extension stays inside national limits on size, height, position and materials. They apply to houses, not flats or maisonettes, and they can be removed by a planning condition or an Article 4 direction, so the property's history matters.
The main limits in England
- Single-storey rear: up to 3 m beyond the original rear wall (4 m for a detached house), no higher than 4 m.
- Larger home extension prior approval: up to 6 m (8 m detached), with neighbours notified and a 42-day decision.
- Within 2 m of a boundary, eaves no higher than 3 m.
- Side extensions: single storey, no more than 4 m high and no wider than half the original house.
- Two-storey rear: no more than 3 m deep and at least 7 m from the rear boundary.
- Extensions and other buildings must not cover more than half the land around the original house.
- Materials of similar appearance to the house (conservatories excepted).
The "original house" means the house as first built, or as it stood on 1 July 1948 if older, so earlier extensions count against the allowances.
When do I definitely need an application?
- Two-storey side extensions and rooms over side garages.
- Most wraparound extensions.
- Anything beyond the permitted development limits.
- Side extensions and two-storey rear extensions on designated land (conservation areas, national parks, National Landscapes, the Broads, World Heritage Sites).
- Listed buildings, which also need listed building consent.
- Flats and maisonettes.
What does planning permission cost in 2026?
In England, from 1 April 2026 the council fee is £548 for a householder planning application, £274 for a lawful development certificate for a proposed extension and £249 for larger home extension prior approval. Drawings and any specialist reports are extra. Fees in Wales, Scotland and Northern Ireland are set separately by each government.
Wales, Scotland and Northern Ireland
Wales: a single-storey rear extension can usually go up to 4 m without an application; two-storey rear extensions need 10.5 m to the rear boundary; there is no prior approval scheme for larger extensions.
Scotland: householder permitted development (Classes 1A and 1B) allows some smaller extensions, and a building warrant is needed before almost any extension is built.
Northern Ireland: single-storey rear extensions up to 3 m (4 m detached) can be permitted development; larger, side and two-storey extensions normally need planning permission from the council.
Should I get a lawful development certificate?
It is not compulsory, but a lawful development certificate confirms in writing that the extension is permitted development. Buyers' solicitors often ask for one, so it can save time when you sell. See our guide to lawful development certificates.
This guide is general information, not legal or professional advice for your property. Rules can change; we check the current position for your address at the survey.