Many single-storey rear extensions fall under permitted development: in England, up to 3m beyond the original rear wall on an attached house and 4m on a detached one, with 6m and 8m possible through the prior approval process. It does not apply to flats or maisonettes, and listed buildings, conservation areas and Article 4 directions all restrict or remove it.
- Permitted development is a set of limits, not a blanket right. Exceed one and you need an application.
- "Original" means as built or as at July 1948 — not as you bought it.
- Prior approval is a neighbour consultation, not a planning application, and it has its own timetable.
- A lawful development certificate is the document a buyer's solicitor will ask for.
The main limits
These are the householder permitted development limits in England for extensions. They apply to houses — not flats or maisonettes — and only where the rights have not been removed.
| Limit | Attached house | Detached house |
|---|---|---|
| Single-storey rear projection | 3m | 4m |
| Same, via prior approval | 6m | 8m |
| Maximum height, single-storey rear | 4m | 4m |
| Eaves height within 2m of a boundary | 3m | 3m |
| Two-storey rear projection | 3m, and 7m from rear boundary | 3m, and 7m from rear boundary |
| Side extension width | Half the width of the original house | Half the width of the original house |
| Side extension storeys | Single storey only | Single storey only |
| Coverage of land around the original house | No more than 50% | No more than 50% |
| Maximum height overall | Not higher than the existing roof | Not higher than the existing roof |
Materials must be similar in appearance to the existing house, no verandas or balconies, and side-facing upper windows must be obscure-glazed and non-opening below 1.7m. Exceed any single limit and the whole thing needs an application.
The word that catches people out: "original"
Permitted development is measured from the original house, which means as it was first built, or as it stood on 1 July 1948 if it predates that.
It does not mean as you bought it. If a previous owner added a conservatory or a small rear extension, that counts against your allowance even though you did not build it.
This is the single most common reason a project someone was confident about turns out to need permission. Before relying on permitted development, establish what has already been added since the original build — old planning records, the title plan, aerial imagery over time, and what the neighbours remember all help.
It applies to the 50% land coverage test too: everything added since the original house counts, including outbuildings.
The prior approval route for larger rear extensions
For a single-storey rear extension beyond the standard 3m or 4m — up to 6m on an attached house and 8m on a detached one — there is a route that is not a full planning application.
You notify the council with details of the proposal. They write to the adjoining neighbours, who have 21 days to object. If nobody objects, the council confirms and you may proceed. If a neighbour does object, the council considers the impact on amenity and decides.
It is quicker and cheaper than a planning application, and the grounds on which it can be refused are narrower — it is specifically about the effect on neighbouring amenity rather than the full range of planning considerations.
The practical implication is worth stating: your neighbours get a formal opportunity to object. Talking to them beforehand is not a legal requirement and it is sensible, because an objection that arrives as a surprise is harder to resolve than one you anticipated.
When permitted development does not apply at all
- Flats and maisonettes. No householder permitted development rights; any extension needs permission.
- Listed buildings. Listed building consent is required in addition to any planning permission, and it covers the fabric itself.
- Conservation areas. Side extensions and cladding lose their permitted development rights, and other limits tighten.
- Article 4 directions. Specific rights have been formally withdrawn for that area.
- National parks, AONBs and World Heritage Sites. Tighter limits apply.
- Where a previous permission removed the rights. New-build estates frequently have a condition doing exactly this, and owners rarely know.
That last one is worth checking on any house built in the last few decades. Conditions attached to the original estate permission commonly remove permitted development rights, and it will not be obvious from the property itself.
Planning is not Building Regulations
These are separate systems and you can need one, both or neither. Confusing them is extremely common.
Planning is about whether you may build it: size, siting, appearance, impact on neighbours and the area.
Building Regulations are about whether it is built safely and performs adequately: structure, insulation, fire, ventilation, drainage.
An extension built under permitted development still needs Building Regulations approval. Inspections happen at defined stages — foundations before concrete, drainage before backfilling — and the output is a completion certificate.
Keep that certificate with the deeds. It is what a buyer's solicitor asks for, and an extension without one causes real friction at sale.
The lawful development certificate
Where you believe your extension is permitted development, you can apply for a Lawful Development Certificate confirming it. It is not permission; it is formal confirmation that permission was not needed.
It costs a fraction of the build and the value shows up years later. Selling a house with a sizeable extension and no paperwork means answering enquiries from a position of "we were told it did not need permission", which satisfies nobody. A certificate settles it in one document.
It is most worth having where the project sits anywhere near a limit — close to the 3m or 4m projection, near the 50% coverage test, or on a property where the original footprint is debatable.
What extensions cost
These are the extension figures published across this site:
| Job | Typical Coventry guide price | Notes |
|---|---|---|
| Build cost | £1,500–£2,500 per m² | Spec dependent |
| Single-storey extension | £20,000–£60,000 | Size & finish dependent |
| Double-storey extension | £100,000+ | Larger projects |
| Average project | ~£30,700 | Across typical jobs |
Planning and Building Control fees sit outside these figures, as do design and structural engineering fees. Where prior approval or a full application is needed, allow for the timetable as well as the fee.
We check the original footprint, what has been added since, and whether the rights have been removed — before any design work.
Frequently asked questions
How far can I extend without planning permission?
In England, a single-storey rear extension may project 3m beyond the original rear wall on an attached house and 4m on a detached one, with 6m and 8m possible through the prior approval process. Other limits apply simultaneously — height, eaves height near a boundary, and the 50% land coverage test — and exceeding any one means an application.
What does "original house" mean?
As the house was first built, or as it stood on 1 July 1948 if it is older — not as you bought it. Anything a previous owner added, including a conservatory, counts against your allowance. This is the most common reason a project someone was confident about turns out to need permission.
What is prior approval for a larger extension?
A route for single-storey rear extensions beyond the standard limits, up to 6m on an attached house and 8m on a detached one. You notify the council, adjoining neighbours have 21 days to object, and if nobody objects the council confirms. It is quicker than a full application and the grounds for refusal are narrower.
Does permitted development apply to flats?
No. Householder permitted development rights apply to houses only, so any extension to a flat or maisonette needs planning permission. There may also be leasehold consents to obtain separately from the freeholder, which is a different process again.
Do I still need Building Regulations if I do not need planning?
Yes. They are separate systems. Planning is about whether you may build it; Building Regulations are about whether it is built safely and performs adequately. An extension under permitted development still needs Building Regulations approval, inspections at defined stages, and a completion certificate at the end.
Should I get a lawful development certificate?
It is optional and usually worth it, particularly where the project sits near a limit. It is formal confirmation that permission was not required, and it is the document that resolves a buyer's solicitor's enquiries in one step years later. The cost is small relative to the build.
Check the status before the drawings
We establish the original footprint, what has been added since and whether the rights still exist — before anyone spends money on design. Free survey.