What size extension can I build without planning permission?
Under permitted development, a single-storey rear extension can be up to 3m deep on a terraced or semi-detached house, or 4m on a detached house — doubling to 6m and 8m under the prior approval process. These rights do not apply in conservation areas or to flats, which covers a significant part of Fulham.
The standard permitted development allowance for a single-storey rear extension is 3m beyond the original rear wall for a terraced or semi-detached house and 4m for a detached one. The Larger Home Extension scheme doubles those to 6m and 8m, but it requires a prior approval application to the council, which notifies your neighbours and gives them 21 days to object. It is not automatic, though it is faster and more certain than a full planning application.
Several other limits apply simultaneously, and breaching any one of them removes the right entirely. The extension must not exceed 4m in height, must not be higher than the highest part of the existing roof, must use materials similar in appearance to the existing house, must not extend beyond the side elevation fronting a highway, and — with all other extensions and outbuildings combined — must not cover more than 50 percent of the land around the original house.
For Fulham the critical caveat is designation. Several parts of the borough, including the Peterborough Estate around Parsons Green, are conservation areas where permitted development rights are restricted, and some streets carry Article 4 directions removing them altogether. Flats and maisonettes never have permitted development rights at any location. We check the specific address against the council's designation map before any design work, because it is the difference between a two-week certificate and a three-month application.
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