Four Oaks Builders / Sutton Coldfield

Extension planning checker

Explore which planning route may suit your extension in England.

Your home & proposed extension

Permitted development means some extensions can be built without a full planning application, if all the rules are met. Larger rear extensions may need a council check called prior approval. Other proposals may need planning permission.

Start with what you know. Use your drawings for measurements, or choose “Not sure” where needed — you do not need to guess.

What sizes are typical?

Most single-storey rear extensions are about 3–5 metres deep and 4–5 metres wide — roughly 12–25 square metres of new floor space. A 4m × 4m extension (about 16 square metres) is a common starting point: enough for a kitchen table and a small seating area. Around 5m × 5m (about 25 square metres) suits a full open-plan kitchen and dining space.

No drawings yet? Use the quick-pick sizes under each measurement below — they are sensible starting points, not rules, and you can change them at any time.

What type of home do you have?

Detached means no shared walls. Semi-detached shares one side; terraced shares walls in a row. Flats and maisonettes have different planning rules.

Where will your extension go?

Rear means behind the house. Side means beside it; wraparound covers both. Two-storey adds space on two floors.

Is your home in a protected area?

This includes conservation areas, National Parks, National Landscapes, the Broads, World Heritage Sites and Sites of Special Scientific Interest (SSSIs). Your council’s planning map can help; choose Not sure if you haven’t checked.

Are there special restrictions on your home?

A listed building is legally protected. An Article 4 direction or a condition on an earlier planning permission can remove some rights to extend. Check council records, or choose Not sure.

How far will it extend behind the original house?

Measure in metres from the original rear wall to the furthest new wall. Original means as first built, or as it stood on 1 July 1948 if older — not the back of a later extension.

metres

Not sure yet

How high will the extension be?

Measure from the ground beside the extension to its highest roof point. Your proposed drawings should show this.

metres

Not sure yet

How high will the bottom edge of the roof be?

This is the eaves height: from the ground to where the outside wall meets the roof, usually near the gutter. For a flat roof, use the eaves measurement on your drawings rather than guessing from the parapet.

metres

Not sure yet

How close will it be to the edge of your property?

Use the shortest gap between the extension and the boundary of your property — often a fence, wall or hedge. If the gap is exactly 2 metres, choose Within 2m.

Permitted development or full planning?

In England, a single-storey rear extension may project up to 4m on a detached house or 3m on other houses, with a maximum height of 4m. Within 2m of a boundary, eaves must not exceed 3m. The larger-home route can allow 8m / 6m respectively, subject to prior approval and other conditions.

This simplified check does not assess previous extensions, original-house limits, garden coverage, materials, roof geometry, highways, protected sites or all planning history. Side, wraparound and two-storey proposals require separate assessment. Flats do not have the same householder rights. Listed-building consent may be needed separately.

Building Regulations, party-wall matters and other approvals remain separate. Confirm the full position before starting work; a lawful development certificate can provide formal confirmation where appropriate.

Planning Portal: extension guidance ↗Government householder guidance ↗