This could include a hip-to-gable conversion, a dormer, forming a mansard roof or any other type of roof addition and/or alteration except a verandah, balcony, raised platform, chimney, flue, or soil or vent pipe. This will not require planning permission provided:
- The highest part of the extension is not higher than the highest point of the original roof;
- It does not project forward of the plane of the existing roof slope on the principal elevation if that elevation faces a highway;
- The total volume of extension added to the roof exceeds 40 cubic metres on a terraced house or 50 cubic metres on a semi-detached or detached house. For purposes of calculating this volume any other addition to the roof must be taken into account, i.e. including any ground- or first-floor extension which has a roof abutting the main roof of the house;
- Except for a hip-to-gable conversion, the extension must be set in at least 20 cms from the eaves, i.e. the bottom of the roof where it overhangs, unless this is not practicable;
- It is not in a National Park, an Area of Outstanding Natural Beauty, a Conservation Area, an area designated under s41(3) of the Wildlife and Countryside Act 1981, the Norfolk Broads or a World Heritage Site;
- It is built using external materials similar in appearance to those on the existing house;
- Any window in the roof slope forming a side elevation is obscure glazed and non-opening unless the parts of the window which can be opened are more than 1.7 metres above the floor of the room in which the window is installed.