Do You Need Planning Permission for an Extension or Loft Conversion?

Rear extensions

A single-storey rear extension can extend up to 4 metres beyond the original rear wall of a detached house, or 3 metres for any other house, and can't be more than 4 metres high. Outside designated land and Sites of Special Scientific Interest, you can go up to 8 metres (detached) or 6 metres (other houses) if you go through the 'prior approval' process, where the council informs the neighbours and considers any objections. These limits come from the Planning Portal's guidance on extensions.

Rules that apply to every extension

Only half the area of land around the original house can be covered by extensions and other buildings. An extension can't be higher than the highest part of the existing roof or higher at the eaves than the existing eaves, and where it comes within 2 metres of a boundary the eaves can't exceed 3 metres. It can't go forward of the front of the house, and it can't include verandas, balconies or raised platforms. Materials must look similar to the existing house. Extensions of more than one storey can't extend more than 3 metres beyond the rear wall or come within 7 metres of the boundary opposite it, and side extensions must be single storey, no more than 4 metres high and no wider than half the original house.

Loft conversions

A loft conversion is permitted development if the extra roof space, including any previous enlargement, doesn't exceed 40 cubic metres for a terraced house or 50 cubic metres otherwise. It can't be higher than the existing roof, can't extend beyond the existing roof slope on the side facing a road, and can't include verandas, balconies or raised platforms, or alter a chimney, flue or soil pipe. Side windows must be obscure-glazed and, if they open, at least 1.7 metres above the floor. The enlargement should be set back at least 20 centimetres from the original eaves where practicable — a rule that is relaxed for hip-to-gable enlargements — and materials must be similar to the existing house.

When you do need to apply

Permitted development doesn't apply to flats and maisonettes, or to homes where a planning condition or an Article 4 direction has removed the rights. Loft conversions aren't permitted development on designated land — conservation areas, Areas of Outstanding Natural Beauty, National Parks, the Broads and World Heritage Sites — and all side extensions on that land need planning permission. A listed building may need listed building consent as well. And any project that goes beyond the limits above needs a householder planning application.

Get it confirmed in writing

If you're relying on permitted development, you can ask your council for a certificate confirming the work is lawful — the FMB puts the fee at around £240 in England. It's optional, but Citizens Advice warns that building without the permission you need can cause problems when you come to sell. Planning permission and building regulations are separate systems, so even a fully permitted project still needs building regulations approval from a building control body.

Cost, timing and the risk of skipping it

The FMB gives the householder planning application fee as £528 in England. The Planning Portal says most householder applications are decided within eight weeks of being validated, and validation takes extra time, so allow at least two months and don't fix a builder's start date until you have a decision. If the work adds more than 100 square metres of floor space it may also attract the Community Infrastructure Levy. Citizens Advice says that if you don't get the permission or approval you need, you might be fined, prosecuted, or made to put things right or undo the work.

Frequently Asked Questions