How big can a rear extension be without planning permission? (England, 2026)

Many single-storey rear extensions in England don't need a planning application, thanks to permitted development rights. These rights come from the Town and Country Planning (General Permitted Development) (England) Order 2015. They have clear size limits, and they do not apply everywhere.

The basic limits for a single-storey rear extension

Measured from the rear wall of the original house (as it was first built, or as it stood on 1 July 1948 if older):

• Attached house (terraced or semi-detached): up to 3 metres deep.
• Detached house: up to 4 metres deep.
• Maximum height of 4 metres, and eaves no higher than 3 metres if the extension is within 2 metres of a boundary.
• Extensions and other buildings must not cover more than half the land around the original house.
• Materials should look similar to the existing house.

Going bigger with prior approval

Outside designated land (see below), you can go up to 6 metres on an attached house and 8 metres on a detached house using the prior approval route, sometimes called the larger home extension scheme.

1. You send the council a prior approval application with a plan, the depth, the height and your neighbours' addresses.
2. The council tells your neighbours, who can object.
3. The council has 42 days to decide. It only looks at the effect on neighbours' amenity, such as light and privacy.
4. Don't start building before you get approval, or before the 42 days have passed without a decision.

Where permitted development doesn't apply (or is limited)

• Conservation areas, National Parks, Areas of Outstanding Natural Beauty (National Landscapes), the Broads and World Heritage Sites ("Article 2(3) designated land"): the larger 6 m / 8 m route is not available, and side extensions need planning permission.
• Flats and maisonettes do not have these householder rights.
• Listed buildings need listed building consent.
• Your council may have removed rights with an Article 4 direction, or a condition on an earlier planning permission. New-build estates often have this.

Planning permission is not the only approval you need

Even when you don't need planning permission:

• You will almost certainly need Building Regulations approval: foundations, structure, insulation, drainage, fire safety and electrics.
• If you build on or near a shared wall or boundary, you may need to serve a Party Wall notice on your neighbour.
• If there is a public sewer under the garden, you may need permission from the water company to build over or near it.

Rules can change

The government has consulted on changes to householder permitted development. The limits above are what applies as of the date at the top of this page. Always check the Planning Portal or ask your council's planning team before you start.

Choosing a builder for an extension

Ask to see extensions they have finished, ask who handles Building Regulations and party wall notices, and get a written quote that says what is and isn't included. On Donereel you can watch videos of a builder's real jobs before you contact them.

Sources

• Planning Portal: extensions, permitted development
• Planning Portal mini guide: single-storey extensions
• The Town and Country Planning (General Permitted Development) (England) Order 2015