Rear extensions
Extensions. Updated 21 September 2026
Most single-storey rear extensions on a house in England can be built without applying for planning permission, under permitted development. The limits are fixed and they are measured from the house as it was first built, or as it stood on 1 July 1948 if older.
The limits
| Terraced or semi-detached | Detached | |
|---|---|---|
| Single storey, depth | 3m | 4m |
| Single storey, depth with prior approval | 6m | 8m |
| Single storey, height | 4m | 4m |
| Two storey, depth | 3m | 3m |
- Eaves no higher than 3m if the extension is within 2m of a boundary.
- Extensions and outbuildings together may cover no more than half the garden and land around the original house.
- Materials must look similar to the house.
- A two-storey extension must be at least 7m from the rear boundary.
When permission is needed
- The house is a flat or maisonette. Permitted development does not apply.
- The house is listed. Listed building consent is needed for almost any change.
- A conservation area, National Park, National Landscape or World Heritage Site: no two-storey rear extensions and no cladding.
- The council has an Article 4 direction on your street. This removes some or all of these rights.
- Rights have been removed by a condition on an earlier permission for the house.
Prior approval
The 6m and 8m depths need prior approval from the council. Neighbours are notified and the council considers the effect on their light and privacy. It takes up to 42 days and is not a full planning application.
Before you build
A Lawful Development Certificate confirms the work is permitted. It is optional, and useful when you sell.
Source: Permitted development rights for householders, technical guidance, Ministry of Housing, Communities and Local Government.
Common questions
Do I need planning permission for a back extension?
Often not. A single-storey rear extension on a house in England is permitted development up to 3m deep on a terrace or semi and 4m on a detached house, and no higher than 4m. Flats, maisonettes and listed buildings need permission.
Can I build a 3m rear extension without planning permission?
Yes, on most houses in England. A single-storey rear extension up to 3m deep is permitted development on any type of house if it is no higher than 4m and meets the other limits. A two-storey one can also be 3m deep if it is at least 7m from the rear boundary.
Can I extend 4 metres without planning permission?
On a detached house, yes: a single-storey rear extension can be 4m deep. On a terrace or semi, 4m needs prior approval from the council, a route that allows up to 6m. Prior approval is not a full planning application.
What is the 50% rule for house extensions?
Extensions and outbuildings together may cover no more than half the land around the original house. The footprint of the original house itself is left out of the sum. Anything beyond that needs planning permission.
How high can you build a single-storey extension?
No higher than 4m under permitted development. Within 2m of a boundary the eaves can be no higher than 3m, and the extension can never be higher than the roof of the house.