Do I need planning permission for a loft conversion?
Usually not, if you stay within a volume allowance and do not change the front roof slope. Dormers are where most loft conversions run into trouble.
The volume allowance
Loft conversions are covered by permitted development, but the allowance is measured in cubic metres of added roof space, not floor area.
| House type | Additional roof volume allowed |
|---|---|
| Terraced house | 40 cubic metres |
| Detached or semi-detached | 50 cubic metres |
That is the total for the property, not per project. Any previous roof enlargement by any owner counts against it. If a former owner added a rear dormer, the volume it added has already been spent.
The rules that catch people out
- Nothing can extend beyond the plane of the existing roof slope on the front elevation, meaning the side facing a highway. This is why front dormers nearly always need planning permission.
- The conversion cannot go higher than the existing highest point of the roof. A roof lift needs permission.
- Materials must be similar in appearance to the existing house.
- Side facing windows must be obscure glazed, and non opening unless the opening part is more than 1.7 metres above the floor.
- No verandas, balconies or raised platforms. A Juliet balcony fitted inside the opening is usually acceptable, a projecting balcony is not.
Rooflights that follow the line of the roof, such as conservation style windows, are the least likely to cause a problem. A large rear dormer is the most common design that stays within permitted development, provided the volume works.
Conservation areas change the answer
In a conservation area, a roof extension that is visible from a highway is not permitted development. In practice that rules out most front dormers and often rear ones too, depending on the layout of the street and whether the rear is visible from a public road or footpath.
Article 4 directions can go further and remove rights over roofing materials or window types. These vary street by street, so you have to check with your own council.
Listed buildings
If your house is listed, the interior is protected as well as the exterior. A loft conversion involves structural work, new openings, insulation and often the removal of original roof timbers, all of which affect character. Listed building consent will be required.
There is no application fee for listed building consent. Carrying out the work without it is a criminal offence under the Planning (Listed Buildings and Conservation Areas) Act 1990.
Flats are different
Householder permitted development rights do not apply to flats or maisonettes. If you own the top floor flat and want to convert the loft above it, you will need planning permission, and you will also need to check your lease and whether you actually own the roof space.
Building regulations always apply
Every loft conversion needs building regulations approval. The main areas are fire escape, floor loading, stair design and headroom, insulation and structural support. This is separate from planning and is not optional.
Party wall matters also come up frequently. If you are cutting into a shared wall to support new beams, you will usually need to serve notice on your neighbour under the Party Wall etc. Act 1996.
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Check your address freeCommon questions
Do I need planning permission for a dormer?
A rear dormer is often permitted development if it stays within your volume allowance and meets the other conditions. A front dormer facing a highway is not permitted development, because nothing can extend beyond the front roof slope. In a conservation area, any dormer visible from a highway needs permission.
Do rooflights need planning permission?
Usually not, if they do not project more than 150mm beyond the plane of the roof slope and do not sit above the highest part of the roof. Conservation areas and listed buildings are the exceptions.
How do I know how much volume I have left?
You need to know whether the roof has been enlarged before, by any previous owner. Old planning records held by your council, and the building's history in the title deeds, are the usual starting points. If the roof has never been altered you have the full 40 or 50 cubic metres.
Can I raise the roof height?
Not under permitted development. Any increase in the overall roof height needs planning permission.
Is a loft conversion worth applying for a certificate for?
If you are relying on permitted development, a certificate of lawful proposed development at £130 gives you written confirmation. Buyers' solicitors ask about loft conversions frequently, so it is a useful document to have at sale.