Do you need planning permission for a house extension?

In England, you often do not need planning permission for a house extension, because permitted development rights cover many extensions. The extension must stay within set limits, and the house must not be somewhere those rights have been restricted (Planning Portal, read October 2026). If you go beyond the limits, or the rights have been removed, you need to apply for householder planning permission.

Check three things first. Whether the property is a flat or maisonette, whether it is on designated land such as a conservation area, and whether an Article 4 direction applies. A yes to any of them changes the answer, so confirm with your council before you measure anything.

This guide covers England. Scotland, Wales and Northern Ireland have their own rules, linked near the end.

What can you build without planning permission?

The Planning Portal summarises the rules in Schedule 2, Part 1, Class A of the General Permitted Development Order 2015. As at October 2026, these are the main limits for a house in England:

The limits count the total enlargement, so earlier extensions use up your allowance. The "original house" means the house as first built, or as it stood on 1 July 1948 if it is older. A previous owner's extension counts against you. The government's technical guidance for householders explains these terms with illustrative examples, and the Planning Portal strongly advises reading it before you rely on a measurement.

What about loft conversions?

Loft conversions have their own permitted development class. As at October 2026, the Planning Portal says a roof enlargement must not add more than 40 cubic metres to the original roof space on a terraced house, or 50 cubic metres on any other house. The house also cannot be on Article 2(3) designated land, which includes conservation areas and National Parks (Planning Portal on loft conversions). If you are weighing up a loft, our page on loft conversion builders is a good place to look for local firms.

What is prior approval for a larger rear extension?

Prior approval lets a single-storey rear extension go further than the 4 and 3 metre limits. The Planning Portal puts the ceiling at 8 metres for a detached house and 6 metres for any other house. The route is not available on Article 2(3) designated land or a Site of Special Scientific Interest (Planning Portal).

You apply to your local planning authority before building, and the council then consults the adjoining neighbours. If they raise concerns, the council must decide whether the effect on the amenity of the adjoining properties is acceptable. That decision determines whether the extension can go ahead (Planning Portal's prior approval guidance). So prior approval is a decision made by the council.

When are permitted development rights restricted or removed?

The householder rules do not apply, or apply in a reduced form, in several cases:

• Flats and maisonettes. The planning rules for flats differ in important ways from those for houses. The permitted development rights for common house projects do not apply to flats (Planning Portal on flats and maisonettes).
• Converted or newly created houses. Houses created through permitted development change-of-use rights usually cannot use householder rights for an extension, so planning permission is usually needed (Planning Portal).
• Article 2(3) designated land. This covers conservation areas, areas of outstanding natural beauty, National Parks, the Broads and World Heritage Sites. On this land every side extension needs planning permission, and so does any rear extension of more than one storey (Planning Portal).
• Article 4 directions. A council can issue a direction removing some or all permitted development rights. The Planning Portal says they are made where the character of an area of acknowledged importance would be threatened, and are most common in conservation areas (Planning Portal).
• Planning conditions. A condition attached to the original planning permission for your house can restrict the rights. The Planning Portal lists planning conditions alongside Article 4 directions as limits on permitted development.
• Listed buildings. The Planning Portal says different requirements apply if the property is listed, so contact the council before you plan anything (Planning Portal).

How do you check before you build?

Start with your council. The Planning Portal's general advice is to discuss a proposal with the local planning authority before any work begins. It notes that councils may charge for pre-application advice. Ask whether your home is in a conservation area, whether an Article 4 direction applies and whether the house has a planning condition that limits extensions.

For written confirmation, apply for a Lawful Development Certificate. It is not compulsory. You apply to the council through the Planning Portal, pay a fee, and can appeal if the application is refused or not decided within eight weeks (Planning Portal on Lawful Development Certificates). Government guidance says work carried out in accordance with a granted certificate must be presumed lawful. The exception is a material change before the work starts, such as a new Article 4 direction (GOV.UK).

An architect can measure your house, set the design against the limits above and tell you which route it falls under before you ask builders to price it. In London, fixed-fee planning and building regulations drawings for extensions and conversions are available from FixedFeePlans. That service covers London only.

What else do you need besides planning permission?

Planning is one of three separate checks, and the other two apply even when no planning application is needed.

• Building regulations. The Planning Portal says most extensions need building regulations approval, with some exempt classes (Planning Portal on building regulations for extensions). A Lawful Development Certificate does not remove that requirement (GOV.UK).
• Party wall. The Party Wall etc Act 1996 covers new building at the boundary of two properties, work to a party wall and excavation near a neighbour's foundations. The owner doing the work must give the neighbour notice, and the Act is separate from planning and building regulations (GOV.UK). It applies in England and Wales.
• Community Infrastructure Levy. Work adding over 100 square metres of floor space may be liable for the levy (Planning Portal).

Once you know the route, you can search for builders near you or browse builders who specialise in extensions. Our guide to house extension costs is a place to start on budget.

What about Scotland, Wales and Northern Ireland?

Everything above applies to England. As at October 2026, the other nations publish their own householder rules:

• Scotland: mygov.scot sets a different test. For example, a single-storey rear extension must not go back more than 3 metres on a terraced house or 4 metres otherwise. It must also be outside a conservation area.
• Wales: the Welsh Government publishes a householder guide and technical guidance, last updated 29 May 2020. The Planning Portal notes that Welsh policy may differ from England's.
• Northern Ireland: nidirect says permitted development has dimension limits for extensions and is restricted in designated areas such as conservation areas.

Common questions

What happens if I build without the right permission?

A planning breach is not in itself illegal, and a council will often accept a retrospective application. If the breach involves a development that was previously refused, or the retrospective application fails, the council can serve an enforcement notice requiring you to put things back. It is illegal to disobey an enforcement notice unless you successfully appeal it (Planning Portal on planning breaches).

Do my neighbours get a say?

A permitted development extension within the standard limits needs no application, so there is nothing for the council to consult on. Under prior approval for a larger rear extension, the council consults the adjoining neighbours. If you make a householder planning application, the council asks your neighbours for their views (Planning Portal on neighbours). The Planning Portal also suggests telling neighbours before you apply or start work.

Can I extend a flat or maisonette?

Not under the householder permitted development rights, which are written for houses. Ask your council whether you need planning permission, and check your lease for what it allows.