What can be built under permitted development rights for loft conversions?

Under permitted development you can make alterations such as small extensions or loft conversions to your house without obtaining planning permission. Due to the rising number of householders planning applications, the Government introduced measures to remove the need for local planning authorities to approve routine loft conversions, house extensions or alterations, which are considered to have minimal impact on neighbours. The rules were updated on the 1st October 2008.
Permitted development is intended to reduce the red tape and encourage home owners to develop their homes. Consequently the good news is that now many loft conversions can be built under permitted development rights.

Allowances:
Under permitted development you are given certain allowances for extending your property. If you live in a conservation area or your house is a listed building your permitted development rights might be restricted under article 4 of the GPDO (General Permitted Development Order Town and Planning Act) if you are unsure you need to check this with your local planning office/council who will be able to advise you.

Loft conversions are considered permitted development subject to the following conditions:

A volume allowance of 40 cubic meters for terraced houses.
A volume allowance of 50 cubic meters for detached and semi-detached houses.
No extension beyond the plane of the existing roof slope of the principal elevation that fronts the highway.
No extension to be higher than the highest part of the roof.
Materials to be similar in appearance to the existing house.
No verandas, balconies or raised platforms.
Side facing windows to be obscured-glazed; any opening to be 1.7m above the floor.
Roof extensions not to be permitted development in designated areas*.
Roof extensions, apart from hip to gables to be set back as far as practicable, at least 20ch from the eaves.
*. Designated areas include national parks and the Broads, Areas of Outstanding Beauty, conservation areas and World Heritage Sites.
Note: You should always contact your local planning authority to discuss your proposal before any work begins to confirm that the development is permitted.