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.
These are specific to "the enlargement of a dwellinghouse consisting of an addition or alteration to its roof" as detailed in Schedule 2, Part 1, Class B of the The Town and Country Planning (General Permitted Development) (England) Order 2015 (as amended).
There are different rules for "any other alteration to the roof of a dwellinghouse" (Schedule 2, Part 1, Class C) which are detailed in our 'Roof' section.
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 original eaves
The roof enlargement cannot overhang the outer face of the wall of the original house.
Please note: For an explanation of how to apply the 20cm set back condition please see pages 35-36 of 'Permitted development for householders - Technical guidance', see below.
*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.
**Designated areas include national parks and the Broads, Areas of Outstanding Natural Beauty, conservation areas and World Heritage Sites.
Please note: The permitted development allowances described here apply to houses and not to:
Flats and maisonettes (view our guidance on flats and maisonettes)
Converted houses or houses created through the permitted development rights to change use (as detailed in our change of use section)
Areas where there may be a planning condition, Article 4 Direction or other restriction that limits permitted development rights.