A single-storey rear extension is the most common house extension in London, and many can be built under permitted development rights, which means a full planning application is not needed. Those rights come with limits, and they do not apply to every home. This guide sets out the main ones so you know what to check first.
The main size limits for a rear extension
- Depth. A single-storey rear extension can usually extend up to 3 metres beyond the back wall of an attached house (a terraced or semi-detached house) and up to 4 metres for a detached house.
- Height. The extension cannot be taller than 4 metres, and the eaves cannot be higher than 3 metres if any part of the extension is within 2 metres of a boundary.
- Coverage. Together, all extensions and outbuildings cannot cover more than half the land around the original house.
- Materials. They need to be similar in appearance to the existing house.
- Position. The extension cannot extend beyond the wall that faces a road at the front of the house.
These are summaries. The full conditions, including how the “original house” is defined, are in the government’s technical guidance linked at the end.
Going deeper: the larger home extension scheme
For single-storey rear extensions deeper than those limits, there is a route called prior approval for larger home extensions, which allows up to 6 metres for an attached house and 8 metres for a detached house. You notify the council, neighbours next door are consulted, and the council decides whether it objects on the grounds of impact on neighbours. It is not a full planning application, but it is a formal process with a fee and a decision.
When permitted development does not apply
- Flats and maisonettes do not have these householder rights.
- Some homes have had permitted development rights removed by an Article 4 direction, and listed buildings have their own rules.
- Extra restrictions apply in conservation areas and other designated land.
- Rights were used up if the house has already been extended, because earlier extensions count towards the limits.
- A planning condition on the original permission can remove them.
Confirming it before you build
Your council will not stop you building something that really is permitted development, but if you are unsure, you can ask for a formal answer by applying for a lawful development certificate. It is also helpful when you later sell. Permitted development covers planning only: the extension still needs Building Regulations approval, and a shared wall may need a party wall notice.
This guide is general information for homes in England and is not legal or planning advice. Rules can change and differ between properties and local authorities, so always confirm the position with your council or a qualified professional.
Read about house extensions or request a quote to talk through your own house.