Planning permission is not normally required. However, permission is required where you extend or alter the roof space and it exceeds specified limits and conditions.
Under new regulations that came into effect from 1 October 2008 a loft conversion for your house is considered to be permitted development, not requiring an application for planning permission, subject to the following limits and conditions:
· A volume allowance of 40 cubic metres additional roof space for terraced houses*
· A volume allowance of 50 cubic metres additional roof space 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 obscure-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 gable ones, to be set back, as far as practicable, at least 20cm from the eaves
*Bear in mind that any previous roof space additions must be included within the volume allowances listed above. Although you may not have created additional space a previous owner may have done so.