Do I need planning permission for a rear extension?
Often no, if your extension stays inside permitted development limits. But those limits are tighter than most people expect, and several things can remove them entirely.
The short answer
A single storey rear extension can usually be built without planning permission under what are called permitted development rights. These are national rights set out in the General Permitted Development Order, and they let you build certain things without applying to the council.
The catch is that permitted development is not a general allowance. It is a long list of precise conditions, and your extension has to meet every single one of them. Miss one and you need planning permission for the whole thing.
How deep you can build
For a single storey rear extension, the depth limit depends on your house type.
| House type | Standard limit | With neighbour notification |
|---|---|---|
| Detached | 4 metres | 8 metres |
| Semi-detached or terraced | 3 metres | 6 metres |
The larger depths in the right hand column come from the neighbour notification scheme, sometimes called the larger home extension scheme. It is not automatic. You apply to the council for prior approval, they write to your neighbours, and if a neighbour objects the council decides whether the impact is acceptable. The fee is £120.
A two storey rear extension is different again. It can go up to 3 metres deep, and it has to sit at least 7 metres from your rear boundary.
Height and boundary limits
- Maximum eaves height of 3 metres if any part of the extension is within 2 metres of a boundary.
- The extension cannot be higher than the highest part of the existing roof.
- Materials must be similar in appearance to the existing house.
- Nothing can project forward of the principal elevation, meaning the face of the house that fronts a highway.
- No verandas, balconies or raised platforms.
The 50 percent rule
This is the one people most often miss. Extensions and outbuildings together cannot cover more than half of the land around the original house. The original house footprint itself does not count towards that figure.
Original house means the house as first built, or as it stood on 1 July 1948 if it is older than that. This matters enormously. If a previous owner built a rear extension twenty years ago, that extension counts against your allowance. You do not get a fresh 3 or 4 metres just because you did not build the first one.
When permitted development does not apply at all
Several things remove or restrict these rights entirely.
Listed buildings
Permitted development technically still exists, but any work affecting the character of a listed building needs listed building consent, which is a separate permission. In practice an extension almost always affects character, so consent is required. There is no fee for a listed building consent application, but doing the work without it is a criminal offence, not just a planning breach.
Conservation areas
Rear extensions of more than one storey are not permitted development in a conservation area. Cladding the exterior is not permitted development either. These restrictions apply automatically to every property in the area, listed or not.
Article 4 directions
Councils can strip out specific permitted development rights in specific streets or areas using an Article 4 direction. There is no national list. You have to check with your own local planning authority.
Flats and maisonettes
Householder permitted development rights do not apply to flats. If you own a flat you will generally need planning permission for external alterations.
Conditions on the original permission
Some houses, particularly on newer estates, had permitted development rights removed by a condition when the estate was approved. This is worth checking on the original planning permission for your property.
Should you get a lawful development certificate
If you build under permitted development you do not need to apply for anything. But you can apply for a certificate of lawful proposed development, which is the council confirming in writing that what you plan is lawful.
It costs £130, which is half the householder application fee. It is not compulsory. It is worth it for anything significant, because when you sell the house a buyer's solicitor will ask how you know the extension was lawful, and a certificate is a much better answer than an opinion.
Do not forget building regulations
Planning permission and building regulations are two separate systems. Almost every extension needs building regulations approval regardless of whether it needs planning permission. Permitted development does not exempt you from building regs, and a lot of people find this out late.
Find out what applies to your address
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Check your address freeCommon questions
Can I build a 4 metre rear extension without planning permission?
On a detached house, yes, if every other permitted development condition is met. On a semi-detached or terraced house the standard limit is 3 metres, and going to 4 metres would need prior approval under the neighbour notification scheme.
Does my neighbour's extension mean I can build the same?
Not necessarily. Every site is assessed separately. Your neighbour may have had planning permission, may have a different house type, or may have had more of their original allowance left. Previous extensions on your own property count against your limits.
What happens if I build without permission?
The council can serve an enforcement notice requiring you to alter or remove the work. For a listed building, unauthorised work is a criminal offence carrying an unlimited fine and up to two years in prison. Enforcement action for most breaches must normally begin within a set time limit, but that is not a reason to rely on it.
How much does a householder planning application cost?
The householder application fee in England is £258. A lawful development certificate for proposed work is £130. Listed building consent is free. Fees change periodically, so confirm the current figure with your council or the Planning Portal.
Does a rear extension need permission if I am in a conservation area?
A single storey rear extension can still be permitted development in a conservation area if it meets the standard conditions. Anything over one storey at the rear is not permitted development there, and an Article 4 direction may remove more rights on top of that.