Do you need planning permission for an extension?

Permitted development rights allow householders in England to make certain changes to a house without applying for planning permission, provided the work meets every limit and condition. If your extension goes beyond any one of them, you need a householder planning application instead. The rules below are the Planning Portal's summary for extensions, which covers England only, and GOV.UK's householder technical guidance gives the same depth, height and land coverage limits.

Permitted development is not a loophole or a guarantee, and your local planning authority has the final say on whether a scheme qualifies. Always check your proposal with your council before you commit to drawings or a builder. Some general conditions apply to every extension, whatever its type.

• Only half the area of land around the original house can be covered by extensions or other buildings.
• An extension must not 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 cannot exceed three metres in height.
• Materials must be of similar appearance to the existing house.

The limits are measured against the "original house", so ask your council how any earlier extensions to your home affect what is left. GOV.UK's technical guidance was last updated in September 2019, so check the current position with your council. If your house has been extended before, gather any old plans or approvals before you design anything new.

The larger home extension scheme lets you go deeper than the standard limits with a single storey rear extension, up to eight metres for a detached house or six metres for any other house. It is not available on Article 2(3) designated land or a Site of Special Scientific Interest, according to the Planning Portal. Instead of a full planning application, you make a prior approval application to your local planning authority.

GOV.UK's technical guidance says householders have to notify the local planning authority, and that works cannot commence until the authority notifies the householder that no prior approval is required, or until 42 days have passed without any decision. GOV.UK gives the fee for a prior approval application for a larger rear extension as £249 from 1 April 2026. If you start before either of those points, you risk building without the approval the scheme requires.

The Planning Portal says the extension rules apply to houses only, and not to flats and maisonettes, converted houses or houses created under certain permitted development rights, other buildings, or areas where there may be a planning condition, Article 4 Direction or other restriction. GOV.UK's guidance confirms that a council can remove permitted development rights through an Article 4 Direction. If any of these applies to your home, you are likely to need a planning application for work that would otherwise be permitted.

On Article 2(3) designated land, which covers conservation areas, Areas of Outstanding Natural Beauty, National Parks, the Broads and World Heritage Sites, all side extensions and all rear extensions of more than one storey need householder planning permission, and exterior cladding is not allowed. Listed buildings need listed building consent for any alteration or extension that would affect their character, and the Planning Portal warns that carrying out such work without consent beforehand is a criminal offence. Parts of Sussex lie in conservation areas and protected landscapes, so check with your local council what applies to your property rather than assuming.

Planning permission and building regulations are two different things, and an extension built under permitted development still needs to meet building regulations. GOV.UK says the regulations cover the construction and extension of buildings, and that you can use your council's building control service or a private registered building control approver. A full plans application gets a decision within 5 weeks, or 2 months with your consent, a building notice lets smaller projects start two days after submission, and GOV.UK warns that the person doing the work could be prosecuted and fined if it does not comply.

The Party Wall etc. Act 1996 is also separate from planning and building regulations, and approval under either does not remove the need to follow it. GOV.UK's explanatory booklet says notice must be given at least one month before building a new wall on the boundary line, at least two months before work to an existing party wall, and at least one month before excavating near a neighbour's foundations. A notice is only valid for a year, and if a neighbour does not respond to a notice for party wall work or excavation, a dispute is deemed to have arisen.

Building control charges vary by council, so check your own council's building control page, or ask a private registered building control approver, which sets its own fee. When you are ready to price the work, Sussex Builder can put you in touch with up to 3 checked local builders for free, no obligation quotes through our extensions page or on 01273 115520. Builders and designers can help you understand which route your project needs, but the decision on planning always rests with your council.