Can I convert my loft without planning permission?
Often, yes. In England a loft conversion is permitted development if the added roof volume stays within 40 m³ on a terraced house or 50 m³ on a semi-detached or detached house, nothing is higher than the existing ridge, no dormer faces a road on the principal elevation, materials look similar to the existing roof, and side windows are obscure-glazed and non-opening below 1.7 m. Building regulations approval is always needed.
What counts towards the 40 or 50 cubic metre allowance?
Any added roof volume counts, including dormers and the extra space created by a hip-to-gable change. Volume added by previous owners counts too. We calculate it from the measured survey before the design is fixed.
Which houses cannot use loft permitted development?
Flats and maisonettes, listed buildings, houses in conservation areas, National Parks, National Landscapes (formerly AONBs), the Broads and World Heritage Sites, and houses where permitted development rights have been removed. These need a planning application.
Do mansard conversions count as permitted development?
Usually not, because a mansard changes the shape of the roof significantly. Most need planning permission, and many councils publish design guidance for them.
What other rules apply?
Dormers should be set back from the eaves where practical (the guidance uses 20 cm), balconies and raised platforms are not permitted, and the work must not extend beyond the outside face of any wall of the original house. A lawful development certificate is the best proof the work complied.
Is it the same in Wales and Scotland?
No. Wales has its own permitted development rules for roofs, and in Scotland dormers usually need planning permission and always need a building warrant before work starts.
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This guide is general information about building work in the UK, not legal or tax advice. Rules change, so check the current position for your property with the council, HMRC or a qualified adviser before relying on it.