Often not. A rear dormer or hip-to-gable conversion on a London house can frequently be built under permitted development, without a planning application. The limits are precise, however, and several common circumstances remove the rights altogether. In practice, the house's designations and planning history decide the route more often than the design does, so we establish them before drawing anything.
The permitted development limits
A loft conversion to a house is normally permitted development where all of the following apply:
- The additional roof volume is no more than 40 cubic metres for a terraced house, or 50 cubic metres for a semi-detached or detached house. Earlier roof extensions count towards the allowance.
- Nothing extends beyond the plane of the roof slope facing the road.
- Nothing is higher than the highest part of the existing roof.
- Materials are similar in appearance to the existing house.
- Side-facing windows are obscure-glazed and non-opening below 1.7 metres above floor level.
- Dormers are set back, so far as practicable, at least 20 centimetres from the eaves.
- There are no verandas, balconies or raised platforms.
When planning permission is required
- Flats and maisonettes. They have no permitted development rights for roof extensions.
- Conservation areas. Roof extensions are not permitted development in a conservation area.
- Article 4 directions. A number of London councils have removed roof extension rights in particular streets.
- Listed buildings. Listed building consent is needed as well.
- Mansards and front dormers. These almost always exceed permitted development. A mansard is often the better answer on a terrace, and councils judge it against the existing roofline: where a street already has an established pattern of mansards, the case is usually more straightforward.
- Rights removed by condition. An earlier planning permission may have withdrawn permitted development rights, which is common on newer estates.
Obtain a lawful development certificate
Where no permission is needed, we still advise applying for a lawful development certificate before work starts. It is the council's formal confirmation that the conversion is lawful. Buyers' solicitors routinely ask for one, and it settles any later question from a neighbour. Its cost is small against the risk it removes.
Other approvals
Every loft conversion needs building regulations approval, covering structure, fire safety and escape, insulation and stairs. If new beams bear on a shared wall, party wall notices must be served on the neighbours, and their timing can set the earliest start date. See when you need a party wall notice.
If the route for your house is unclear, send us the address. We check planning history, conservation status and Article 4 directions as part of a first visit. More on our loft conversion service.