Do I Need Planning Permission for an Extension?

Published 3 April 2026

Planning a house extension is one of the most common home improvement projects in the UK. But before you start drawing up plans, you need to answer a crucial question: do you actually need planning permission?

The answer depends on the size, position, and type of extension you're building - plus where your property is located. Many extensions fall under permitted development (PD) rights, meaning you can build without a formal planning application. Others require full planning permission from your local council.

What Is Permitted Development?

Permitted development rights are a set of national rules, defined in the Town and Country Planning (General Permitted Development) (England) Order 2015 (commonly called the GPDO 2015), that allow certain types of building work without needing to apply for planning permission.

For house extensions, the key rules are found in Schedule 2, Part 1, Class A of the GPDO. These set out precise limits on what you can build under PD.

It's important to understand that permitted development is not a free-for-all. You still need to comply with building regulations, and you may still need to notify your council through a prior approval process for larger rear extensions.

Single-Storey Rear Extensions

Single-storey rear extensions are the most common type of home extension. Under permitted development, you can extend:

Detached houses: up to 4 metres from the rear wall (or 8 metres under the larger home extensions scheme with prior approval)
Semi-detached and terraced houses: up to 3 metres from the rear wall (or 6 metres under the larger home extensions scheme with prior approval)

Additional rules apply:

Maximum eaves height of 3 metres
Maximum overall height of 4 metres
The extension must not extend beyond the side wall of the original house facing a highway
Materials must be similar in appearance to the existing house

The Larger Home Extensions Scheme

Since 2019, the larger home extensions scheme has been made permanent. This allows you to extend up to 8 metres (detached) or 6 metres (semi-detached/terraced) under a prior approval process. Your council must consult adjoining neighbours, who have 21 days to raise concerns. The council then decides within 42 days.

Two-Storey Extensions

Two-storey extensions are subject to stricter PD rules:

Maximum depth of 3 metres from the original rear wall
Must be at least 7 metres from the rear boundary
Maximum eaves height must not exceed the existing house eaves
The roof pitch must match the existing house
No upper-floor side-facing windows unless obscure-glazed and non-opening below 1.7 metres

Two-storey extensions are not permitted under PD if your property is in a conservation area, AONB, National Park, the Broads, or World Heritage Site.

Side Extensions

Single-storey side extensions are allowed under PD, but with conditions:

Maximum width of half the width of the original house
Maximum height of 4 metres
Maximum eaves height of 3 metres
Must not extend beyond the front wall of the original house facing a highway

For side extensions on properties that front a highway, the extension must be single storey and no wider than half the original house width. Two-storey side extensions are also possible under PD but must not be closer than 2 metres to any boundary that adjoins the curtilage.

When You Definitely Need Planning Permission

You will need to apply for planning permission if:

Your extension exceeds the PD size limits described above
You live in a conservation area, AONB, National Park, the Broads, or a World Heritage Site (stricter PD limits apply)
Your property is a listed building (PD rights are significantly restricted; you'll also need listed building consent)
Your property is a flat or maisonette (no PD rights for extensions)
An Article 4 direction is in place that removes PD rights in your area
Your property has already been extended and the cumulative additions exceed PD limits
You want to build forward of the principal elevation facing a highway

Article 4 Directions

Some councils impose Article 4 directions that remove certain PD rights in specific areas. These are common in conservation areas, historic town centres, and areas with a particular architectural character. If an Article 4 direction applies to your property, you may need planning permission even for work that would normally be permitted development.

You can check whether an Article 4 direction applies to your property by searching on your local planning authority's website.

How to Check: Lawful Development Certificate

If you're unsure whether your extension falls under PD, you can apply for a Lawful Development Certificate (LDC). This is a formal confirmation from your council that your proposed work is lawful. It costs around £103 (half the planning application fee) and gives you a legally binding document you can show to buyers, mortgage lenders, and building control.

We strongly recommend getting an LDC for any significant extension, even if you're confident it's permitted development. It protects you against future disputes.

How Much Does Planning Permission Cost?

If you do need to apply for planning permission, the current application fee for a householder extension in England is £258 (as of 2025/26). Use our planning fee calculator to check the exact fee for your project type.

Beyond the application fee, you'll likely need architectural drawings (£1,000–£3,000) and potentially other supporting documents. Read our full guide to planning permission costs for a detailed breakdown.

Tips for a Successful Extension

Talk to your neighbours first. Even if you don't need planning permission, a courtesy conversation can prevent complaints and objections.
Check your title deeds. Some properties have restrictive covenants that limit building work regardless of planning rules.
Use a good architect. A well-designed extension that respects the character of your home and neighbourhood is far more likely to succeed. Find a local architect through our directory.
Don't forget building regulations. Even permitted development extensions need to comply with building regulations for structural safety, insulation, drainage, and fire safety.

Summary

Many house extensions in the UK can be built under permitted development rights without needing planning permission. The key is understanding the size limits for your property type and checking whether any restrictions (conservation area, Article 4, listed building) apply to your home.

When in doubt, apply for a Lawful Development Certificate or seek pre-application advice from your local planning authority. It's far cheaper than discovering a problem after you've started building.