Do I need planning permission for an extension?

Q: Do I need planning permission for an extension?

Not always. In England many single-storey rear extensions are permitted development: broadly up to 3 metres deep on a semi or terrace and 4 metres on a detached house, no higher than 4 metres. Two-storey side extensions, most double-storey extensions and flats need a planning application, listed buildings need consent, and conservation areas have narrower rights.

What is permitted development?

Permitted development is a national grant of planning permission for certain small works, so you do not need to apply to the council. It only applies to houses, not flats or maisonettes, and it can be removed by a planning condition or an Article 4 direction. In conservation areas, National Parks and National Landscapes the rights are narrower.

The main limits for extensions in England

Single-storey rear: up to 3 m deep (attached house) or 4 m (detached), maximum 4 m high.
Larger home extension: up to 6 m or 8 m through the prior approval process, where the council considers neighbours’ comments.
Two storeys: rear only, no more than 3 m deep and at least 7 m from the rear boundary.
Side: single-storey only, up to 4 m high and no wider than half the original house.
Eaves within 2 m of a boundary no higher than 3 m, and no more than half the garden covered.
Materials similar in appearance to the house.

Lofts and porches

Rear dormers can be permitted development within 40 m³ of extra roof volume on a terraced house and 50 m³ on others, as long as they do not face the road. Porches up to 3 m² in ground area and 3 m high, at least 2 m from a road boundary, are also covered.

Getting certainty

A lawful development certificate from the council confirms that a project is permitted development. It is optional, but buyers’ solicitors often ask for one when you sell.

Wales, Scotland and Northern Ireland

Each nation has its own rules. Wales allows single-storey rear extensions of up to 4 metres under its own rules but has no larger home extension route. Scotland’s householder rights for extensions and dormers date from 2012 (current guidance: Circular 1/2024), and a building warrant is usually needed before an extension starts. Northern Ireland’s 2015 order allows rear extensions of 3 metres (4 metres detached) and controls dormers by set-backs rather than a volume limit. See our guide to the differences.

Sources and further reading

This guide is general information, not legal or tax advice. Rules change and depend on your property; we confirm what applies to your project at the survey.