Does a rear extension need planning permission?

Some rear extensions in England can use permitted development rights. Others need prior approval or a planning application. The answer depends on the house, the complete design and any restrictions on the property, not just how far the extension projects into the garden.

Check the whole scheme, not one measurement

For a qualifying house, the usual single storey rear projection limits are 4 metres for a detached house and 3 metres for other houses, measured from the original rear wall. These are only part of the permitted development rules.

Height, boundaries, materials, previous enlargements and the amount of land covered also matter. Householder rights do not apply to flats, and some houses have restricted rights. Read the government's householder technical guidance before treating any measurement as permission to build.

Larger extensions have a separate process

Eligible single storey rear extensions can project up to 8 metres from a detached house or 6 metres from another house through the larger home extension process. Additional conditions apply, and the route is unavailable on certain protected land.

You must notify the council before building. It consults adjoining neighbours and may need to assess the effect on their amenity. A neighbour objection is not, by itself, an automatic refusal. Follow the official prior approval guidance and establish the outcome before starting work.

When to apply for planning permission

If the scheme falls outside permitted development, a planning application lets the council assess it against relevant policy and other material considerations. Falling outside the permitted development limits does not itself mean a scheme will be refused.

Start with the council's current planning policies and the site's planning history. A nearby extension can offer a useful comparison, but its permission does not transfer to your property. Compare the design and circumstances, then read the actual decision and any conditions.

When a lawful development certificate helps

For proposed work that meets permitted development rules, a lawful development certificate provides a formal council determination of lawfulness. It is a different question from whether a planning application has an acceptable design.

The evidence must describe the actual proposal clearly. Keep the certificate and its drawings together, and check any later design change against them. See the government's lawful development certificate guidance.

Use local decisions as evidence

Explore single storey rear extension decisions in Wandsworth, or find your own planning authority. Look at the decision count and period alongside each rate. Archived project groups may mix application routes, and a historical approval share is not your personal chance of success. Our planning data methodology explains those limits.

Move from a check to drawings

Our rear extension drawings service starts with a free address check. Phase 1 planning starts from £995 for a standard single-storey rear extension, with the scope and fixed fee agreed before instruction. It is paid only on approval; council and Portal charges are separate and paid at submission. Building regulations is a separate optional stage, quoted individually and paid on instruction if you go on to build.

Planning and building regulations are separate requirements. Check the government's building regulations guidance before construction, even if the extension does not need a planning application.

For other home improvements, see our permitted development rights overview and lawful development certificate guide.