Do You Need Planning Permission for an Extension or Loft?

Rear extensions

Under permitted development, a single-storey rear extension is limited to 3 m beyond the rear wall of the original house for most houses and 4 m for detached houses. The larger-home-extension prior approval route allows up to 6 m for most houses and 8 m for detached houses, but this route is not available on designated land.

The maximum height of a single-storey rear extension is 4 m.

Two-storey rear extensions must not extend more than 3 m beyond the original rear wall and must be at least 7 m from the rear boundary.

Side extensions and total site coverage

A side extension must be single storey, no more than 4 m high and no wider than half the width of the original house.

Extensions and outbuildings together cannot cover more than half the land around the original house.

Loft conversions

For loft conversions under permitted development:

• The volume allowance is 40 cubic metres for terraced houses and 50 cubic metres for other houses.
• The work must not extend beyond the existing roof slope on the front of the house.
• It cannot exceed the height of the existing roof.
• Materials must look similar to those already used on the house.
• Balconies and raised platforms are not allowed.

When permitted development is restricted

Permitted development rights do not apply to flats and maisonettes. They are also more restricted in conservation areas and other designated land.

Building Regulations approval is normally needed even when planning permission is not.

Not sure? Ask your council for a Lawful Development Certificate before you build.

Check the current rules on the Planning Portal or speak to your local council.