Do you need planning permission for a house extension?

Rules called permitted development rights let you extend a house in England without a planning application, as long as specific limits and conditions are met. Go beyond them and you will most likely need householder planning permission. This guide follows the Planning Portal's summary of the limits (Planning Portal). It covers England only. The Planning Portal says policy in Wales may differ, and Scotland and Northern Ireland have their own systems, so ask your local planning authority there.

First check that permitted development applies to your home

The rules summarise Schedule 2, Part 1, Class A of the Town and Country Planning (General Permitted Development) (England) Order 2015, as amended. They do not apply to:

• flats and maisonettes
• houses that were converted, or created through certain permitted development rights such as changes of use and new dwellinghouses
• other buildings
• areas where a planning condition, an Article 4 direction or another restriction limits or removes permitted development rights

An Article 4 direction is issued by a local planning authority. It removes some or all permitted development rights, for example in a conservation area or around a listed building. Your council can tell you whether one covers your street (Planning Portal).

Limits that apply to every extension

These conditions apply to every type of extension. They are measured against the original house. That means the house as first built, or as it stood on 1 July 1948. Earlier extensions count towards the limits, including ones a previous owner built. The list below is the Planning Portal's summary of the conditions (Planning Portal).

• Extensions and other buildings can cover no more than half the area of land around the original house.
• An extension cannot be higher than the highest part of the existing roof, or higher at the eaves than the existing eaves.
• Within two metres of a boundary, the eaves height cannot exceed three metres.
• It cannot be built forward of the principal elevation (the main front of the house) or, where the house fronts a highway, the side elevation.
• It cannot include verandas, balconies or raised platforms, a microwave antenna, a chimney, flue or soil and vent pipe, or any alteration to the roof of the existing house.
• Materials must look similar to those on the existing house.

Single-storey rear extensions

A single-storey rear extension cannot be more than four metres high. How far it can project from the original rear wall depends on the house type. It also depends on whether you use the prior approval route.

Prior approval is not available on designated land or on a Site of Special Scientific Interest. You apply to the local authority, which consults the adjoining neighbours. If they object, the authority decides whether the effect on their amenity is acceptable (Planning Portal, prior approval). The application fee is £249 (fees guide).

As a worked example using only these limits: a semi-detached house on ordinary land wants a single-storey extension that goes 5 metres back. That is over the 3 metre standard limit and inside the 6 metre prior approval limit, so the prior approval route is the one to look at. At 7 metres it would need a full householder application.

Side extensions and extensions of more than one storey

A side extension that goes beyond the side elevation of the original house must meet three tests:

• a single storey only
• no more than four metres high
• no wider than half the width of the original house

All side extensions of more than one storey need householder planning permission (Planning Portal). An extension of more than one storey has its own limits:

• It must not extend more than three metres beyond the rear wall of the original house.
• It must not come within seven metres of any boundary opposite the rear wall.
• The roof pitch must match the existing house as far as practicable.
• Any upper-floor window in a side elevation must be obscure-glazed and non-opening, unless the opening part is more than 1.7 metres above the floor.

Conservation areas, National Parks and other designated land

The Planning Portal calls this Article 2(3) designated land (Planning Portal). It covers conservation areas, areas of outstanding natural beauty, areas specified by the Secretary of State to protect the countryside, the Broads, National Parks and World Heritage Sites. On that land:

• all side extensions need householder planning permission
• all rear extensions of more than one storey need householder planning permission
• the work cannot include cladding of the exterior
• prior approval for the larger single-storey rear extension is not available

Five checks before you rely on permitted development

1. Is it a house, not a flat or maisonette?
2. Is it free of planning conditions and Article 4 directions that remove the rights? Ask your council.
3. Is it on designated land? If so, all side extensions and all rear extensions of more than one storey need householder planning permission, and prior approval is not available.
4. Does the total, counting every earlier extension, stay within the half-the-land limit?
5. Does each dimension stay within the limit for its type of extension?

When you do need to apply

If your plans go beyond any limit or condition, the Planning Portal says a householder application is likely to be required. In England the fee is £548 for an application to enlarge, improve or alter a single dwellinghouse (not flats), applying from 1 April 2026 (fees guide). You pay it to the council. It is separate from what you pay a designer or architect; our guide to what an architect costs explains how those fees work. A design change can sometimes bring a scheme back inside the limits, so it is worth asking an architect before you apply. You can browse architects who take on extensions in the directory.

Getting certainty with a Lawful Development Certificate

A Lawful Development Certificate is a legal document, granted by the local planning authority, stating that a proposal would be lawful. Apply for one when you are not sure whether a permitted development proposal is lawful. It is not a replacement for planning permission, and any development it does not cover still needs permission separately (Planning Portal). For a proposed use or operation the fee is half the full application fee (fees guide). If you are in London, FixedFeePlans, which is part of the same network as this site, lists certificate of lawfulness drawings from £950 on its price list as at 11 October 2026.

Planning permission is only one of the permissions

Even where no planning application is needed, other rules can still apply. Building regulations approval is a separate process, and the Planning Portal describes the building notice route as often used for alterations or extensions on a home (Planning Portal). The Party Wall etc. Act 1996 is also separate from planning permission and building regulations (GOV.UK); our loft conversion guide explains how its notices work. If the work adds over 100 square metres of floor space, it may also be liable for the Community Infrastructure Levy (Planning Portal).

Once you know what you are allowed to build, you can get prices against the same drawings. You can compare local builders on published prices and verified reviews.