Class A
Do I need planning permission for a rear extension?
Anatolie Chiriac · Graduate Architectural Technologist
Last reviewed August 2026. Relates to England. General guidance, not advice on a specific property.
For most houses in England, a single-storey rear extension can be built without a planning application. It falls under what's called permitted development — rights granted nationally by the General Permitted Development Order, Schedule 2, Part 1, Class A. But those rights come with hard limits, and going a few centimetres over any one of them takes the whole scheme out of permitted development.
The limits that matter most
- Depth: a single-storey rear extension can project up to 4m from the original rear wall for a detached house, or 3m for a semi-detached or terraced house.
- Height: no more than 4m to the highest point. If any part sits within 2m of a boundary, the eaves height must not exceed 3m.
- Coverage: extensions and outbuildings together must not cover more than half the land around the original house.
- Position: nothing may project beyond a wall forming the principal elevation, or a side wall fronting a highway.
- Materials: the exterior must be of similar appearance to the existing house.
The word ‘original’ does a lot of work
Limits are measured against the house as it was originally built, or as it stood on 1 July 1948 for older properties — not as it stands today. If a previous owner already added a rear extension, that volume counts against your allowance. This is the single most common reason a scheme people believed was permitted development turns out not to be.
Going deeper: the prior approval route
Deeper single-storey rear extensions — up to 8m for a detached house or 6m for others — are possible under the larger home extension provisions, but they require a prior approval application to the council first, with neighbours given the chance to object. It is not a formality, and it is not the same as permitted development.
When permitted development doesn’t apply at all
Flats and maisonettes have no householder permitted development rights. Listed buildings, and houses subject to an Article 4 direction, lose some or all of them. In conservation areas, national parks, AONBs and World Heritage Sites — collectively ‘Article 2(3) land’ — side extensions and cladding are excluded and other limits tighten.
The safest way to be sure
If a scheme is close to any limit, or the property’s history is unclear, a Lawful Development Certificate from the council gives you a formal, legally binding confirmation that the work is lawful. It costs a fraction of a planning application and it is what a buyer’s solicitor will ask for when you sell.
This article is general guidance on the position in England and is not advice on a specific property.
Whether these rules let you build what you have in mind depends on measured dimensions and your property’s planning history — neither of which can be settled from an article. If you want a view on your own house, send us the details.
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