Do you need planning permission for an extension?

What is permitted development?

Permitted development rights let you make certain changes to a house without applying for planning permission. In England they come from the General Permitted Development Order 2015, as amended, and they cover extensions, loft conversions, porches and outbuildings, each with its own limits and conditions.

The rights apply to houses only. They do not apply to flats or maisonettes, so any extension to a flat needs a planning application. They can also be removed: a council can do this with an Article 4 direction, often in conservation areas, or through a condition on the original planning permission for your home, which is common on newer estates. Check with your council before you rely on them.

The size limits for extensions in England

The limits are measured from the original house, which means the house as it was first built, or as it stood on 1 July 1948 if it is older. Earlier extensions, even by previous owners, count towards the limits. These are the main rules from the Planning Portal and the government's technical guidance.

• Single-storey rear extension: no deeper than 3 metres from the original rear wall for an attached house, or 4 metres for a detached house, and no higher than 4 metres
• Within 2 metres of a boundary: the eaves can be no higher than 3 metres
• Two-storey rear extension: no deeper than 3 metres, and at least 7 metres from the rear boundary
• Side extension: single storey only, no higher than 4 metres, and no wider than half the width of the original house
• Coverage: extensions and other buildings can cover no more than half the land around the original house
• No extension forward of the principal elevation, or of a side elevation that fronts a road
• Materials of a similar appearance to the existing house, and no verandas, balconies or raised platforms

Larger rear extensions and prior approval

In England, a single-storey rear extension can go further, up to 6 metres for an attached house or 8 metres for a detached house, through the larger home extension route. This is not available on designated land, such as conservation areas, National Parks and Areas of Outstanding Natural Beauty, or on a Site of Special Scientific Interest.

You must notify your council through a prior approval application before work starts. The council tells your adjoining neighbours and gives them the chance to object. If they do, the council considers only the impact on neighbouring homes, such as loss of light or privacy. You can start once the council confirms that prior approval is not needed or is granted, or if 42 days pass without a decision.

Listed buildings and conservation areas

If your home is listed, you will almost certainly need listed building consent for an extension, as well as any planning permission. Consent covers changes that affect the building's character, inside and out. The Planning Portal warns that carrying out work that needs listed building consent without getting it first is a criminal offence.

Conservation areas and other designated land, such as National Parks and Areas of Outstanding Natural Beauty, have tighter permitted development rules in England. Side extensions and rear extensions of more than one storey need a planning application, cladding the outside is not allowed, and the larger home extension route does not apply. Your council's website will show whether you are in a conservation area or covered by an Article 4 direction.

Planning permission and building regulations are different

Planning is about whether you can build something: its size, appearance and effect on neighbours and the area. Building regulations are about how it is built: structure, fire safety, insulation, drainage and ventilation. Permitted development does not remove the need for other approvals.

Almost every extension needs building regulations approval in England and Wales, through your council's building control service or a registered building control approver. In Scotland, you need a building warrant from the council before work starts. If your extension is close to or on a shared wall, the Party Wall etc. Act 1996 may also require you to give your neighbours notice in England and Wales.

How to be sure: a lawful development certificate

Permitted development is something you work out yourself, and the council does not sign it off. If you want certainty, for example to show a buyer's solicitor later, you can apply to your council for a lawful development certificate. It confirms that the work is lawful and does not need planning permission.

The Planning Portal's interactive guides help you check the limits, and many councils offer pre-application advice. Rules can change, so always check the current guidance on the Planning Portal or gov.uk before you commit to a design.

The rules in Scotland, Wales and Northern Ireland

In Scotland, mygov.scot explains that a single-storey rear extension can be permitted development if it goes back no more than 3 metres on a terraced house or 4 metres on other houses, among other limits, and is not in a conservation area. Extensions of more than one storey must be at least 10 metres from the boundaries. You will still need a building warrant.

In Wales, the gov.wales guidance allows a single-storey rear extension of up to 4 metres on any house, with a 4 metre height limit. For a rear extension of more than one storey, the ground floor can project up to 4 metres and the upper floor up to 3 metres, and it must be at least 10.5 metres from the rear boundary. Extensions of more than one storey are not permitted development in conservation areas.

In Northern Ireland, permitted development is set by its own order. Nidirect says flats and maisonettes need planning permission, and so do changes to listed buildings and many works in conservation areas and Areas of Outstanding Natural Beauty. Nidirect advises speaking to your council's planning office before you start.

How AYS can help

When you know what you want to build, describe the project on AYS, add photos, measurements and any drawings, and local builders who cover your postcode can send free, no-obligation quotes. Ask each builder how they handle building control inspections and how they will stage the work.

Questions people also ask