From 1 October 2008 an extension or addition to your home will be considered to be permitted development, not requiring an application for planning permission, subject to the following limits and conditions:

• More than half the area of land around the "original house"* would be covered by additions or other buildings.
• No extension forward of the principal elevation or side elevation fronting a highway.
• No extension to be higher than the highest part of the roof.
• Maximum depth of a single-storey rear extension of three metres for an attached house and four metres for a detached house.
• Maximum height of a single-storey rear extension of four metres.
• Maximum depth of a rear extension of more than one storey of three metres including ground floor.
• Maximum eaves height of an extension within two metres of the boundary of three metres.
• Maximum eaves and ridge height of extension no higher than existing house.
• Side extensions to be single storey with maximum height of four metres and width no more than half that of the original house.
• Two-storey extensions no closer than seven metres to rear boundary.
• Roof pitch of extensions higher than one storey to match existing house.
• Materials to be similar in appearance to the existing house.
• No verandas, balconies or raised platforms.
• Upper-floor, side-facing windows to be obscure-glazed; any opening to be 1.7m above the floor.
• On designated land* no permitted development for rear extensions of more than one storey.
• On designated* land no cladding of the exterior.
• On designated* land no side extensions.

* The term "original house" means the house as it was first built or as it stood on 1 July 1948 (if it was built before that date). Although you may not have built an extension to the house, a previous owner may have done so.

* Designated land includes national parks and the Broads, Areas of Outstanding Natural Beauty, conservation areas and World Heritage Sites.

The Planning Portal has a useful tool which allows you to work out whether you need planning permission.