Permitted development rights are set out in the Town and Country Planning (General Permitted Development) (England) Order 2015, Schedule 2, Part 1. They allow common house extensions to go ahead without a planning application, provided every limit and condition in the relevant class is met. If any one of them is not met, the whole extension needs planning permission. The figures below are a summary of the main limits; the Order and the government's technical guidance give the full detail.
Rear and side extensions (Class A)
| Limit | Detached house | Semi-detached or terraced house |
|---|---|---|
| Single-storey rear extension: maximum depth beyond the original rear wall | 4 m (up to 8 m with prior approval) | 3 m (up to 6 m with prior approval) |
| Maximum height of a single-storey extension | 4 m | 4 m |
| Within 2 m of a boundary: maximum eaves height | 3 m | 3 m |
| Two-storey rear extension: maximum depth | 3 m, and at least 7 m from the rear boundary | 3 m, and at least 7 m from the rear boundary |
| Side extension | Single storey, maximum 4 m high, no wider than half the width of the original house | Same |
Extensions and other buildings together must not cover more than half of the land around the original house, materials must be similar in appearance to the existing house, and nothing can be built forward of the principal elevation facing a highway. Side extensions and two-storey extensions are not permitted development in conservation areas.
Loft conversions and dormers (Class B)
- Additional roof volume of no more than 40 cubic metres for a terraced house and 50 cubic metres for a detached or semi-detached house, including any earlier roof extensions.
- No part of the extension can be higher than the highest part of the existing roof, or extend beyond the plane of the roof slope that forms the principal elevation and faces a highway.
- Dormers should normally be set back at least 20 cm from the eaves.
- Side-facing windows must be obscure-glazed and non-opening unless the opening part is more than 1.7 m above the floor.
- No verandas, balconies or raised platforms.
- Not permitted development in conservation areas.
Hip-to-gable conversions can be permitted development if they meet these limits, but the volume allowance is used up quickly. Measure it properly before you rely on it.
Rooflights (Class C)
Rooflights are generally permitted development provided they do not protrude more than 15 cm beyond the plane of the roof slope, are no higher than the highest part of the roof, and any side-facing rooflight is obscure-glazed and non-opening below 1.7 m.
Garden rooms and outbuildings (Class E)
- Must be incidental to the enjoyment of the house: a garden room, office or gym is fine, but not separate living accommodation.
- Single storey, with eaves no higher than 2.5 m.
- Maximum overall height of 4 m with a dual-pitched roof, or 3 m for any other roof. Within 2 m of a boundary, the overall height cannot exceed 2.5 m.
- Not forward of the principal elevation, and together with other buildings no more than half the land around the house.
- No verandas, balconies or platforms higher than 30 cm.
Why a Lawful Development Certificate matters
A Lawful Development Certificate (LDC) is the council's formal confirmation that a proposal is permitted development. You do not have to get one, but it is the only reliable way to know before you build, and buyers' solicitors will usually ask for one when you sell. If a scheme turns out not to be permitted development after it has been built, the only route is a retrospective planning application, which costs time, money and certainty. We now check the planning route, and ask for the evidence, before any project starts.
Remember building regulations
Planning and building regulations are separate. An extension or loft conversion that is permitted development still needs building regulations approval, and party wall notices may be needed too. See our guides to the Party Wall Act and to fire safety in loft conversions.