How far can I extend without planning permission?

Under permitted development in England, a single-storey rear extension can usually project up to 3 metres from the original rear wall of an attached house, or 4 metres for a detached house. Larger extensions of up to 6 or 8 metres may be possible through the prior approval process.

Does permitted development mean I don't need building regulations?

No. Planning and building regulations are separate. Most extensions still need building regulations approval even when planning permission isn't required.

Do these rules apply in Scotland, Wales and Northern Ireland?

No. This guide covers England. The other UK nations have their own planning rules, so check the relevant government or council guidance.

Estimate it 3 min read

Do I need planning permission for a rear extension?

The Estimo team · Published 19 October 2026

The short answer

In England, many single-storey rear extensions can be built under permitted development without a full planning application, provided they stay within set size and height limits. Flats, maisonettes, listed buildings and some protected areas have different rules, so always check with your council or the Planning Portal first.

Planning permission and permitted development

Planning permission is the council's approval for a development. Permitted development rights let some smaller changes go ahead without a full planning application, because the government has already granted permission for them nationally, within set limits.

Rear extensions are one of the most common uses of these rights. Whether yours qualifies depends on the size of the extension, the type of property and where it is.

💡 This guide covers England only and is general information. Rules change and local restrictions can apply, so check the Planning Portal and your council before you commit.

The main limits for a single-storey rear extension

Under permitted development in England, a single-storey rear extension generally needs to meet conditions including:

Depth: no more than 3 metres beyond the original rear wall for an attached house, or 4 metres for a detached house.
Height: no higher than 4 metres overall.
Eaves: if within 2 metres of a boundary, eaves no higher than 3 metres.
Coverage: the extension, together with other buildings, must not cover more than half the land around the original house.
Materials: similar in appearance to the existing house.

"Original" means the house as it was first built, or as it stood on 1 July 1948 if older. If a previous owner already extended, that counts against your allowance.

The larger home extension route

Some houses can go further — up to 6 metres for an attached house or 8 metres for a detached one — through a process called prior approval. You notify the council, neighbours are consulted, and the council considers the impact on them before deciding. It is quicker and lighter than a full application, but it is not automatic.

Homes where the rules differ

Permitted development rights may be restricted or removed in several situations:

Flats and maisonettes don't have the same householder rights.
Listed buildings need listed building consent for most works.
Conservation areas, National Parks and Areas of Outstanding Natural Beauty have tighter limits.
Article 4 directions let councils remove specific rights locally.
Planning conditions on newer estates sometimes remove rights entirely.

If any of these might apply, ask the council before designing anything.

A Lawful Development Certificate gives certainty

If you're confident your extension falls within permitted development, you can still apply for a Lawful Development Certificate. It is optional, but it confirms the work is lawful — useful when you come to sell, because buyers' solicitors often ask.

Planning is only one part

Even with no planning application, other approvals usually apply:

Building regulations cover structure, insulation, drainage and fire safety. See GOV.UK's building regulations approval guide.
The Party Wall etc. Act 1996 may apply if you build on or near a shared boundary. See GOV.UK on party walls.
Restrictive covenants in your title deeds can limit building regardless of planning.

How this affects cost

Planning route affects cost and timing. A full application adds fees, drawings and waiting time; prior approval adds a shorter wait; permitted development with a certificate adds a smaller fee. Our guide to what drives the cost of an extension covers the building side.

Next steps

Measure from the original rear wall, check whether your home has any restrictions, and confirm with the Planning Portal or your council. Then use Estimo's extension cost calculator to get a personalised estimate for the size you're allowed to build.

Sources

Frequently asked questions

How far can I extend without planning permission?: Under permitted development in England, a single-storey rear extension can usually project up to 3 metres from the original rear wall of an attached house, or 4 metres for a detached house. Larger extensions of up to 6 or 8 metres may be possible through the prior approval process.
Does permitted development mean I don't need building regulations?: No. Planning and building regulations are separate. Most extensions still need building regulations approval even when planning permission isn't required.
Do these rules apply in Scotland, Wales and Northern Ireland?: No. This guide covers England. The other UK nations have their own planning rules, so check the relevant government or council guidance.

Estimo gives indicative, AI-assisted guidance based on the information provided. It is not a formal quotation, valuation, survey or professional advice. Always confirm with a qualified professional before committing money.