Do you need planning permission for a house extension?
In England, many house extensions can be built under Permitted Development (PD) rights — meaning you do not need to apply for planning permission. But the rules are more specific than most homeowners realise, and the exceptions are significant.
The key factors that determine whether your extension needs planning permission: the size and height of the extension, where it sits relative to the original house, whether you have a detached, semi-detached, or terraced property, whether you are in a restricted area, and whether your PD rights have been removed.
Permitted development rules for rear extensions
Single-storey rear extensions
Detached houses: up to 6 metres from the original rear wall, or up to 8 metres under the Larger Home Extension scheme (with prior approval). Semi-detached and terraced houses: up to 3 metres from the original rear wall, or up to 6 metres under the Larger Home Extension scheme (with prior approval).
Additional conditions: maximum height at the eaves of 3m (4m at the ridge); maximum height of 4m overall; does not cover more than half the garden; materials must match the existing house.
Double-storey rear extensions
Double-storey extensions are more restricted: up to 3 metres from the original rear wall. The roof pitch must match the existing house. There must be no windows or doors on the upper floor side elevation within 1 metre of the side boundary. A minimum 7 metres must remain between the rear of the extension and the rear boundary.
Side extensions
Single-storey side extensions are permitted development if they do not exceed half the width of the original house. Extensions on the principal elevation (front of the house) always need planning permission.
The Larger Home Extension scheme
For single-storey rear extensions that exceed the basic 3m or 6m thresholds, homeowners in England can apply under the Larger Home Extension scheme. This allows extensions up to 6m (semi/terraced) or 8m (detached) provided: prior approval is obtained from the local authority, neighbours are notified and given the opportunity to object, and the authority assesses impact on amenity.
Prior approval applications take 42 days. This is different from planning permission.
When you always need planning permission
Planning permission is always required for: extensions that exceed the PD volume or dimension thresholds; extensions on listed buildings (which also need Listed Building Consent); extensions in National Parks, AONBs, World Heritage Sites, or Conservation Areas that alter the external appearance from the road; properties where permitted development rights have been removed by an Article 4 Direction; flats and maisonettes (PD rights apply to houses only).
How to check whether PD applies to your property
The most reliable method: apply for a Lawful Development Certificate (LDC) from your local planning authority. This is a formal confirmation that your proposed works are permitted development and do not need planning permission. An LDC costs £103 (England, 2026) and provides legal certainty.
Building Regulations always required
Even if your extension does not need planning permission, Building Regulations approval is always required for: structural work, thermal insulation to Part L standards, fire safety, electrical work, plumbing and drainage connections, and means of escape from upper floors.