In most cases, a loft conversion is considered to be Permitted Development, not requiring planning permission, provided certain limits and conditions are met. However, householders should be advised to apply for a certificate of lawfulness to confirm that the proposed works are lawful.
To fall within Permitted Development, any additional roof space created must not exceed these volumes:
- 40 cubic metres for terraced houses
- 50 cubic metres for detached and semi-detached houses
Any previous roof space additions must be included within this volume allowance.
No part of the extension is to be higher than the highest part of the existing roof.
No extension beyond the plane of the existing roof slope of the principal elevation that fronts the highway.
Side-facing windows to be obscure-glazed; any opening to be 1.7m above the floor.
Roof extensions, apart from hip to gable ones, to be set back, as far as practicable, at least 20cm from the original eaves.
The roof enlargement cannot overhang the outer face of the wall of the original house.
Planning permission is required for a Loft Conversion:
- In certain Conservation Areas (see Conservation area guidance document)
- Where the property is subject to an Article 4 Direction
- Listed Building
- Designated Land