Many single-storey extensions in England can be built without a planning application, using permitted development rights. Whether your project qualifies depends on your house, where it is, and the size of what you want to build.
Check your house has permitted development rights
Flats and maisonettes do not have householder permitted development rights. Listed buildings need listed building consent for most works. Homes in conservation areas, National Landscapes and National Parks have reduced rights, and councils can remove rights in an area with an Article 4 direction. Some newer homes had their rights removed by a condition on the original planning permission, so it is worth checking the planning history of your house.
The main size limits for rear extensions
A single-storey rear extension can usually extend 3 metres beyond the original rear wall of an attached house, or 4 metres for a detached house, up to 4 metres high. A larger extension of up to 6 metres (attached) or 8 metres (detached) is possible through prior approval, a quicker process in which the council considers only the impact on neighbours.
Two-storey rear extensions are limited to 3 metres in depth and must be at least 7 metres from the rear boundary. Extensions and outbuildings together must not cover more than half the garden around the original house.
Side extensions
A side extension under permitted development must be single storey, no more than 4 metres high, and no wider than half the width of the original house. Anything extending beyond the front of the house needs planning permission.
Get it confirmed in writing
Permitted development needs no application, but a Lawful Development Certificate from your council confirms your extension is lawful. Buyers’ solicitors often ask for one when you sell, so it is worth applying before you build.
If your project falls outside permitted development, you will need a householder planning application with existing and proposed drawings.
This guide is general information about the rules in England, not advice on your property. Always check with your council before you build.