Any major modification or extension to your home may require formal approval from your local authority planning department to ensure it complies with local guidelines. However, since a change to the national planning guidelines in late 2008, the majority of loft conversions comprising Velux-style roof windows and many types of dormer have become exempt from requiring planning permission — provided they conform to the revised rules set out under the national legislation. The legislation, known as permitted development (PD) rights, allows modifications to properties without the need for planning permission, subject to the following limits and conditions:
- A volume allowance of 40 cubic metres for terraced houses
- A volume allowance of 50 cubic metres 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
Full details can be found on the UK Planning Portal.