Do I Need Planning Permission for an Extension?

Permitted Development: What You Can Usually Build

Under the Town and Country Planning (General Permitted Development) (England) Order 2015 (as amended), many extensions can be built without a full planning application. The key limits for residential extensions:

Single Storey Rear Extensions

Note: The 6m/8m limits are the default — they were temporarily extended to 6m/8m for detached houses from 2021 to 2025, and some local authorities have adopted different rules. Always verify with your local planning authority.

Double Storey Extensions

Double storey rear extensions on semi-detached or terraced houses almost always require planning permission because they are closer to the boundary at first-floor level and can affect neighbours' light significantly.

When Full Planning Permission Is Required

• Any extension that exceeds the permitted development limits (depth, height, proximity to boundary)
• Side extensions of more than one storey (single storey side extensions are usually permitted)
• Extensions within a conservation area (even single storey rear may need consent)
• Listed buildings (Listed Building Consent is always required, separate from planning)
• Extensions on flats or maisonettes (different permitted development rules apply)
• A property that has already used its PD rights (e.g., a previous rear extension)
• Extensions that would be visible from the road on a designated heritage asset

Prior Approval: A Faster Route

For larger single storey rear extensions that exceed the standard PD limits, you can use the Prior Approval process. This is faster than a full planning application:

• You notify the local authority of the proposed extension
• They consult with neighbours and the highway authority
• The focus is on neighbour notification and impact — not the principle of the extension
• Decision typically in 28 days (vs 8 weeks for full planning)
• Fees are lower: £206 for prior approval vs higher for full application

Other Considerations

• Building Regulations — always required, even if planning isn't. A separate building regulations application must be submitted.
• Party Wall Act — if building within 3m of a neighbour's property (or within 6m where the works affect their structure), you must serve a Party Wall Notice.
• Highway authority — if the extension extends to the front or side of the house and affects a public highway or pavement, additional approvals are needed.
• Article 4 Direction — some local authorities have removed permitted development rights in certain areas. Always check with your local planning authority.

How to Check Your PD Rights

The easiest route is to check with your local planning authority — either via their website or a pre-application advice meeting. Many now offer free or low-cost written confirmation of what you can do.

You can also use the planning portal's permitted development tool, but this is a general guide — always verify with your local authority for your specific property.