Do You Need Planning Permission for a Single-Storey Extension?

Planning a single-storey extension is one of the most popular home improvement projects in the UK — and for good reason. A well-designed rear or side extension can add significant living space and value to your home. But before you call a builder, you need to know whether you'll need planning permission. In 2026, the rules haven't changed dramatically, but plenty of homeowners still get caught out. This guide covers everything you need to know.

Permitted Development Rules for Single-Storey Extensions

Under Permitted Development (PD) rights, you can extend your home without applying for full planning permission, provided you meet specific criteria. For single-storey rear extensions in England, the key limits are:

• Detached houses: Up to 4m depth from the original rear wall
• Semi-detached and terraced houses: Up to 3m depth from the original rear wall
• Maximum height: 4m at the ridge; 3m at the eaves if within 2m of a boundary
• Side extensions: Width must not exceed half the width of the original house
• Materials: Must be similar in appearance to the existing house
• No verandas, raised platforms or balconies are permitted under PD rights

The "original house" refers to the building as it was on 1 July 1948, or as it was first built if built after that date. Crucially, any extensions already built since that date count towards your total allowance — so if a previous owner added a 2m rear extension, a detached homeowner only has 2m of PD allowance remaining.

For a deeper dive into all the rules, see our complete guide to Permitted Development rules in the UK.

The Larger Home Extension Scheme

There is also a "Larger Home Extension Scheme" (sometimes called the Prior Approval neighbour consultation scheme) that allows bigger extensions — up to 8m depth for detached houses and 6m for other houses — but this requires a Prior Approval application (see below).

When Planning Permission IS Required

Even if your extension would normally fall within PD limits, you'll need full planning permission in several circumstances:

• Conservation areas, National Parks, AONBs or World Heritage Sites: PD rights are restricted. Side extensions almost always need permission, and even rear extensions may require it depending on the local authority.
• Listed buildings: All works require Listed Building Consent, separate from (and in addition to) planning permission.
• Article 4 Directions: Local councils can remove PD rights in specific areas using Article 4 directions. Always check with your local planning authority (LPA).
• Flats and maisonettes: PD rights for extensions do not apply to flats.
• New-build homes: Some new-build estates have had PD rights removed as a condition of their original planning consent.
• Exceeding size limits: Going beyond the 4m/3m depth or the maximum height automatically requires planning permission.

If your home is in a sensitive area, always check with your local planning department before starting any work. You'll also want to understand your obligations under the Party Wall Act if you're building near a shared boundary.

The Prior Approval Process

If you want a larger extension (up to 8m for detached, 6m for other houses) under the Larger Home Extension Scheme, you need to apply for Prior Approval from your local planning authority before work starts. Here's how the process works:

1. Submit a Prior Approval application to your LPA (usually a simple form and drawings)
2. Your LPA notifies adjoining neighbours, who have 21 days to raise objections
3. If no objections, or objections aren't significant, you get Prior Approval
4. If neighbours object, the LPA assesses the impact on amenity
5. The LPA must decide within 42 days of receipt

Prior Approval is a lighter-touch process than full planning permission, and most straightforward applications are approved. The fee is currently £120. You can only use the scheme for extensions that stay within the larger size limits and meet all other PD criteria.

Wondering what your extension will cost once you have permission? Our guide to single-storey extension costs in the UK covers typical prices in detail.

Extension Scenarios: PD Allowed or Planning Permission Required?

What to Do Before You Build

Even when planning permission isn't required, there are other important steps before starting work on a single-storey extension:

• Building Regulations approval: Almost all extensions need Building Regs sign-off, regardless of planning. This covers structural integrity, insulation, drainage and fire safety. See our building regulations guide for the full process.
• Party Wall Notice: If you're building at or near a shared boundary or excavating close to a neighbour's foundations, you may need to serve a Party Wall Notice.
• Certificate of Lawful Development: Even if you don't need permission, it's worth applying for a Certificate of Lawful Development. This provides formal confirmation your extension is lawful and is very useful when you come to sell.
• Find a reputable builder: Use our guide on how to hire a builder in the UK to avoid costly mistakes.

Frequently Asked Questions