Planning permission
Do you need planning permission for a rear extension?
- Covers
- rear extension, kitchen extension, back extension, single-storey extension, two-storey extension, conservatory, orangery
- The law
- GPDO 2015, Schedule 2, Part 1, Class A, paragraphs A.1, A.2 and A.3
- Applies to
- England
Short answer
Often not, in England. A rear extension to a house is permitted development under Class A of Part 1 of the General Permitted Development Order 2015 if it stays inside every limit. A single-storey extension can project up to 3 metres beyond the rear wall of the original house, or 4 metres on a detached house, and be up to 4 metres high. An extension of more than one storey can project up to 3 metres and must stay at least 7 metres from the rear boundary.
Break one limit and the whole extension needs planning permission. Flats have no such rights, and on Article 2(3) land, which includes conservation areas, a rear extension of more than one storey always needs permission.
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The limits
| Limit | Single storey | More than one storey | Order |
|---|---|---|---|
| Depth beyond the original rear wall | 3 m, or 4 m detached | 3 m | A.1(f), A.1(h) |
| Height | 4 m, and not above the existing roof | Not above the existing roof | A.1(f), A.1(c) |
| Eaves | Not above the existing eaves | Not above the existing eaves | A.1(d) |
| Any part within 2 m of a boundary | Eaves 3 m at most | Eaves 3 m at most | A.1(i) |
| Rear boundary | No distance set | At least 7 m away | A.1(h) |
| Ground covered by buildings other than the original house | Half the land around it at most | Same | A.1(b) |
| On Article 2(3) land | Same limits | Not permitted | A.2(c) |
Materials must look similar to the house (a conservatory is exempt), upper-floor side windows must be obscure-glazed and not open below 1.7 metres above the floor, and a platform more than 0.3 metres high is excluded (A.3, A.1(k), paragraph I). Where the new work joins an earlier extension, the limits apply to the two together (A.1(ja)). Up to 6 metres, or 8 metres detached, is possible for a single storey through prior approval.
Development is not permitted by Class A if ... the enlarged part of the dwellinghouse would be within 2 metres of the boundary of the curtilage of the dwellinghouse, and the height of the eaves of the enlarged part would exceed 3 metres
Three things that catch people out
The line is the original rear wall. Depth is measured from the rear wall of the house as built, or as it stood on 1 July 1948 if older (article 2(1)). An earlier owner's extension does not move it. See the original house.
The 2 metre rule limits two storeys and flat roofs. A two-storey extension has eaves well above 3 metres, so it must stand at least 2 metres from every boundary. The technical guidance measures a flat roof's eaves where the wall meets the top of the roof, ignoring any parapet, so a flat roof on the boundary is capped at 3 metres there, not 4.
The 7 metres is to your own boundary. Ruling on the same rule in the 1995 Order, the High Court held that it is measured to the boundary of the house being extended, not to the house behind (Royal Borough of Kensington and Chelsea v SSCLG [2015] EWHC 2458 (Admin), paragraphs 51 to 59). The wording substituted into the Order in 2016 says "the dwellinghouse being enlarged".
A worked example
A semi-detached house, not on Article 2(3) land and never extended. The plot is 7 metres wide, with 14 metres from the original rear wall to the rear boundary. The house is 6 metres wide, built against the party boundary, with eaves 5.4 metres high.
| Check | Single storey, 3 m deep, flat roof | Two storeys, 3 m deep |
|---|---|---|
| Depth, limit 3 m | 3 m: passes | 3 m: passes |
| Eaves within 2 m of a boundary, limit 3 m | 3 m: passes (3.2 m would fail) | 5.4 m: fails unless 2 m from both side boundaries |
| Rear boundary, limit 7 m | No limit | 11 m: passes |
The single storey qualifies at full width if its roof is no higher than 3 metres at the walls. The two storeys qualify only if set 2 metres in from each side boundary, which leaves them 3 metres wide.
What this means for you
Measure from the original rear wall, check every row, and run your figures through the permitted development checker. Check that no planning condition or Article 4 direction has removed the rights (articles 3(4) and 4). Building Regulations and the Party Wall Act apply either way.
Getting certainty
The Order does not ask you to tell the council about an extension within these limits. For proof a buyer or lender will accept, apply for a lawful development certificate under section 192 of the Town and Country Planning Act 1990. From 1 April 2026 the fee is £274, half the £548 householder fee, and the council has 8 weeks to decide.
Sources
- GPDO 2015, Schedule 2, Part 1 legislation.gov.uk
- GPDO 2015, article 2, interpretation legislation.gov.uk
- Permitted development rights for householders: technical guidance, September 2019 gov.uk
- Royal Borough of Kensington and Chelsea v SSCLG [2015] EWHC 2458 (Admin) caselaw.nationalarchives.gov.uk
- Planning Portal: application fees in England from 1 April 2026 planningportal.co.uk