The short answer
Most London loft conversions do not need planning permission. They are permitted development under Class B (roof enlargements) and Class C (rooflights) of the General Permitted Development Order, provided they stay inside the limits below. Every loft conversion still needs building regulations approval.
The limits that matter in 2026
- Added roof volume: 40 m³ for terraced houses, 50 m³ for semi-detached and detached. Previous roof enlargements count.
- No part higher than the existing ridge.
- No enlargement on the principal elevation that faces a highway — no front dormers.
- Rear dormers set back at least 20 cm from the original eaves.
- Materials similar in appearance to the existing house.
- No verandas, balconies or raised platforms.
- Side-facing windows obscure-glazed and non-opening below 1.7 m.
Where it does not apply
- Flats and maisonettes — no householder PD rights.
- Conservation areas — Class B is removed; dormers need planning.
- Article 4 directions — check the exact wording; many West London streets have them.
- Listed buildings — listed building consent for almost everything.
Is a Lawful Development Certificate worth it?
Yes, almost always. The application fee is around £270 in England, the council has eight weeks to decide, and the certificate is what a buyer's solicitor will ask for when you sell. Without it you are relying on your own interpretation of the rules — and so is your buyer.
What Plan Check adds
We run your house and project through the Class B rules, check the conservation and Article 4 position at your address, pull the dormers approved and refused on your street, and tell you whether to go LDC, prior approval or full planning — with a cost band for the build.
General information for England, not advice on your property. Rules change; we check the current position in every report.