An extension or addition to your house is considered to be permitted development, not requiring an application for planning permission, subject to the following limits and conditions:

• No 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.
• Single-storey rear extension must not extend beyond the rear wall of the original house* by more than three metres if an attached house or by four metres if a detached house.
• In addition, outside Article 1(5) designated land* and Sites of Special Scientific Interest the limit is increased to 6m if an attached house and 8m if a detached house until 30 May 2016.
• These increased limits (between 3m and 6m and between 4m and 8m respectively) are subject to the neighbour consultation scheme.
• Maximum height of a single-storey rear extension of four metres.
• Extensions of more than one storey must not extend beyond the rear wall of the original house* by more than three metres.
• 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.

For more information please follow the link below to the UK Government’s Planning Portal.

http://www.planningportal.gov.uk/permission/commonprojects/extensions/

Typically, the fee for enlarging, improving or altering an existing dwelling will now be £172 and the cost of obtaining outline planning permission for a dwelling will be £385.

• approving development proposals that accord with the development plan without delay; and
• where the development plan is absent, silent or relevant policies are out‑of‑date, granting permission unless:
  • any adverse impacts of doing so would significantly and demonstrably outweigh the benefits, when assessed against the policies in this Framework taken as a whole; or
  • specific policies in this Framework indicate development should be restricted.