For most houses in England, the answer is 3 metres, or 4 metres if your house is detached — and up to 6 or 8 metres through a notification process called prior approval. Flats get nothing, and conservation areas change the picture considerably.
Here is how the rules actually work.
Permitted development, in one paragraph
Permitted development rights are a national grant of planning permission. If your project stays inside a set of published limits, you can build without applying for planning permission. Go a centimetre beyond them and you need a full application. The rights apply to houses, not flats, and they are reduced in protected areas.
Single-storey rear extensions
| Detached house | Semi-detached or terraced | |
|---|---|---|
| Depth beyond the original rear wall | 4m | 3m |
| Maximum height | 4m | 4m |
| Eaves height within 2m of a boundary | 3m | 3m |
Two details catch people out:
"Original" means the house as first built, or as it stood on 1 July 1948 if it's older. If a previous owner added a kitchen extension in 1995, that counts against your allowance even though you never saw it.
Extensions and outbuildings together can't cover more than half the garden around the original house.
Going deeper: 6m and 8m
You can build a single-storey rear extension of up to 6 metres (semi-detached or terraced) or 8 metres (detached) under the larger home extension scheme. It isn't automatic:
- You submit details to the council with a fee of £249
- The council writes to your adjoining neighbours, who have at least 21 days to comment
- If a neighbour objects, the council decides whether the impact on them is acceptable
- If the council doesn't decide within 42 days, you may proceed
This route isn't available in conservation areas or other protected land.
Two-storey and side extensions
Two storeys at the rear: up to 3 metres deep, and no closer than 7 metres to the rear boundary. Upper-floor side windows must be obscure-glazed and non-opening below 1.7m. Not permitted in conservation areas.
Side extensions: single storey, maximum 4 metres high, and no wider than half the width of the original house. Not permitted in conservation areas.
When you have no permitted development rights at all
- You live in a flat or maisonette. Householder permitted development applies to houses only.
- Your home was created through a permitted change of use, such as an office conversion.
- An Article 4 direction covers your street — councils use these to protect the character of an area.
- A planning condition removed the rights, which is common on newer housing estates.
- Your home is listed, where separate listed building consent is needed and unauthorised work is a criminal offence.
In a conservation area the rights are reduced rather than removed: a modest single-storey rear extension may still be possible, but side extensions, two-storey rear extensions, roof extensions and cladding are not.
Should you get a certificate?
Permitted development doesn't require paperwork, but a Lawful Development Certificate is the council formally confirming your project is lawful. It costs £274 in England.
We recommend it in most cases. Buyers' solicitors ask for it, it settles any argument with a neighbour, and it is far cheaper than discovering a problem after the work is built.
Permitted development isn't always the better answer
It is quicker and more certain, but it is a one-size-fits-all rulebook. A planning application can often produce a better home: a deeper extension suited to your plot, a wraparound combining side and rear, a better roof form, or glazing that permitted development wouldn't allow.
We look at both routes before recommending one.
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