Planning & Regulations
The permitted development limits for rear, side and two-storey extensions, the larger extension route, and the places where stricter rules apply.
Many extensions in England can be built without a full planning application, under what are called permitted development rights. Whether yours qualifies depends on the type of house, how far the extension reaches, how tall it is and where the property is. Here are the limits, and the situations where you will need planning permission.
For a single-storey rear extension to a house, the key limits are:
Other types of extension have their own limits:
| Type of extension | Permitted development limits |
|---|---|
| Single-storey rear | Up to 3m deep (4m detached), up to 4m high. Eaves no higher than 3m within 2m of a boundary. |
| Larger single-storey rear (prior approval) | Up to 6m deep (8m detached), after notifying the council through a prior approval application. Not available on Article 2(3) land or a Site of Special Scientific Interest. |
| Side extension | Single storey only, up to 4m high, and no wider than half the width of the original house. |
| Two-storey rear | No more than 3m beyond the original rear wall, and not within 7m of the boundary opposite the rear wall. Roof pitch should match the house. |
If you want a single-storey rear extension deeper than the standard limits, you can go up to 6m for a semi-detached or terraced house, or 8m for a detached house, through the prior approval process. You notify your local planning authority, which considers the impact on neighbours before you build.
Permitted development rights can also be removed by an Article 4 direction or a condition on an earlier planning permission, so it is worth checking your property's planning history with the council.
Conservation areas and the Cotswolds National Landscape are "Article 2(3) land". There, all side extensions and all rear extensions of more than one storey need planning permission, exterior cladding is not permitted development, and the 6m/8m prior approval route is not available.
Yes, in most cases. Planning permission is about how the extension looks and affects its surroundings; building regulations are about how it is built. Most extensions need building regulations approval even when they do not need planning permission. Building control checks areas including:
| Area | Area |
|---|---|
| Foundations and walls below ground | Drainage |
| External and internal walls | Roofs |
| Doors and windows | Electrics |
| Kitchens and bathrooms | Energy efficiency and ventilation |
If your extension is close to a neighbour's property you may also need to serve notice under the Party Wall Act. See do I need a party wall agreement for my extension?
How we help: before quoting, we check whether your extension falls within permitted development, needs prior approval or needs a full application, and we work with your designer on the building regulations drawings so the build is approved first time.
We can visit the site, explain what your project needs and give you a clear, itemised quote.
A single-storey rear extension can usually reach 3m beyond the original rear wall of a semi-detached or terraced house, or 4m for a detached house. Through the prior approval process this can increase to 6m and 8m, except on Article 2(3) land.
Sometimes. A rear extension of more than one storey can be permitted development if it reaches no more than 3m beyond the original rear wall and is at least 7m from the boundary opposite. Any side extension of more than one storey needs planning permission.
The house as it was first built, or as it stood on 1 July 1948 if it was built before then. Extensions added since count towards your allowances.
Yes, in most cases. Most extensions need building regulations approval even when they do not need planning permission.
No. Householder permitted development rights apply to houses, not flats or maisonettes, so extensions to flats need planning permission.
This article is general guidance for England, correct when last reviewed. Rules differ in Wales and can be changed locally (for example by Article 4 directions or planning conditions), so check with your local planning authority or building control before starting work.