The short answer
Many loft conversions on houses in London do not need a full planning application, because they can be built under permitted development rights. But those rights come with limits, they do not apply to every property, and every loft conversion – with or without planning – needs Building Regulations approval.
Permitted development: the main conditions
A loft conversion on a house is usually permitted development if it meets conditions including:
- The extra roof space created is no more than 40 m³ for terraced houses, or 50 m³ for semi-detached and detached houses (including any previous roof extensions).
- No part of the extension is higher than the highest part of the existing roof.
- Nothing extends beyond the plane of the existing roof slope at the front of the house facing the road.
- Materials are similar in appearance to the existing house.
- There are no verandas, balconies or raised platforms.
- Side-facing windows are obscure-glazed and non-opening below 1.7 m from the floor.
- Dormers are set back, as far as practicable, at least 20 cm from the original eaves.
When you will need planning permission
- Flats and maisonettes – permitted development rights for houses do not apply.
- Conservation areas – roof extensions are not permitted development, so an application is needed.
- Article 4 directions – some councils remove permitted development rights on particular streets.
- Listed buildings – listed building consent is required.
- Mansards and other designs that exceed the limits above, such as front dormers.
A Lawful Development Certificate
Even when planning permission is not needed, we usually recommend applying to your council for a Lawful Development Certificate. It confirms in writing that the work is permitted development – reassuring for you, and very useful when you come to sell.
Building Regulations are always required
Every loft conversion must meet Building Regulations, covering structure, fire safety (including a protected escape route and fire doors), insulation, ventilation, stairs and headroom. A Building Control inspector checks the work at key stages and issues a completion certificate at the end. We coordinate this on every project.
The Party Wall Act
If you live in a terraced or semi-detached house, work such as inserting steel beams into the shared wall falls under the Party Wall etc. Act 1996. You must serve notice on your neighbours before starting – typically two months ahead for work to a party wall. Neighbours can agree, or appoint a surveyor. We explain the process and help you plan the timing.
Not sure where your home stands?
Rules depend on your exact address, so the quickest way to know is a free survey. We will check your property's planning position and recommend the best type of conversion – see our pages on dormer, hip-to-gable, mansard and rooflight conversions.
This guide is general information about the rules in England, not legal advice. Always check your specific property with your local council.
