Not always. In England many single storey extensions to houses are permitted development, so no planning application is needed, provided they stay within national limits on depth, height, width, position and materials. Most extensions beyond those limits, homes in conservation areas, flats and listed buildings need an application. Building regulations approval is almost always needed.
The rules below come from the government’s permitted development rules for householders and the Planning Portal, checked on 13/10/2026. Miss a single limit and the whole extension needs an application.
What extensions can you build without planning permission?
Under permitted development you can build a single storey rear extension up to 4 metres deep on a detached house, or 3 metres on any other house, within height, width, position and materials limits. Larger single storey rear extensions, up to 8 or 6 metres, are possible through prior approval. Two storey extensions have tighter limits again.
The main limits, as the Planning Portal states them:
- Coverage. No more than half the area of land around the original house can be covered by extensions or other buildings.
- Height. No higher than the highest part of the existing roof, and no higher at the eaves than the existing eaves.
- Near a boundary. Within 2 metres of a boundary, the eaves cannot exceed 3 metres.
- The front. Nothing forward of the principal elevation or, where it fronts a highway, the side elevation.
- Single storey rear. No more than 4 metres beyond the rear wall of the original house if detached, 3 metres otherwise, and no more than 4 metres high.
- Side extensions. Single storey, no more than 4 metres high, and no wider than half the width of the original house.
- Two storey or more. No more than 3 metres beyond the rear wall of the original house, and not within 7 metres of any boundary opposite the rear wall.
- Materials. Similar in appearance to the existing house.
“Original house” means the house as it was first built, or as it stood on 1 July 1948 if it was built before then. Extensions added since count against these limits. Our house extension service shows the single storey, double storey and wrap around schemes we design and build.
What is the 50% rule for house extensions?
The 50% rule is a permitted development limit: extensions and other buildings around your house must not cover more than half of the land around the original house. The measure excludes the footprint of the original house but includes later extensions, sheds, garages and garden rooms. Exceed it and the new extension needs a planning application.
In the words of the government’s technical guidance, the limit “covers all buildings”, including any later extensions or separate buildings, even those built before 1948.
What is a larger home extension?
It is the prior approval route for bigger single storey rear extensions: up to 8 metres on a detached house or 6 metres on any other house. You notify the council, which gives your neighbours the chance to object. The technical guidance says work cannot start until the council confirms prior approval is not required, grants it, or 42 days pass without a decision.
The route is not available on designated land such as conservation areas, or on a Site of Special Scientific Interest. The official council fee for a larger home extension prior approval is £249, per the government’s planning fees schedule from 1 April 2026.
When does an extension need planning permission?
When it breaks any permitted development limit, or when the property has no permitted development rights:
- Designated land. In conservation areas, National Parks, the Broads and World Heritage Sites, among others, side extensions, rear extensions of more than one storey and cladding of the exterior are not permitted development.
- Flats and some converted houses. The rights apply to houses only.
- Removed rights. Councils can remove rights with an Article 4 direction, and earlier permissions sometimes remove them by condition. Check your property’s planning history.
- Listed buildings. Works affecting character need listed building consent, and often planning permission as well.
Local rules sit on top of the national ones.
How long does planning take for an extension?
The statutory period for deciding a householder application in England is eight weeks from a valid application, unless you and the council agree a longer period in writing, according to GOV.UK’s planning guidance. Before that come the drawings, and any advice you ask the council for first.
The same guidance sets a planning guarantee: if an application that is not major development is still undecided after 16 weeks, with no agreed extension of time, the fee is refunded. The official householder fee in England is £548 from 1 April 2026, per the government’s fees schedule, plus a Planning Portal service charge of £75.83 plus VAT if you apply through the Portal. These are published official fees, not Madisons prices.
Should you get planning before asking builders for prices?
Craig Bellamy, founder of Madisons, says yes in his film on whether planning should be approved before you ask for prices: “you need to make sure your planning is done and awarded.” Without approval there is no engineering pack, and builders end up pricing guesses. His sequence: “architect, planning submission, approval, engineer, take the whole pack, hand that out, tender to the builders”.
The alternative he offers is to start with design and build, where Madisons can “build a project and planning award around what fits your budget”. That is how our turnkey design and build service runs.
Watch the film with its transcript: Should planning be approved before I ask for prices?
Who draws the plans for a planning application?
Usually an architect or designer. Asked whether you need to get an architect, Craig answers in his film: “If you want to, yes. If not, give us a shout. We can manage the whole process from start to finish.” Madisons works with two or three architects regularly, each suited to different kinds of project, and builds the design team around yours.
Watch the film with its transcript: Do I need an architect for an extension?
Does an extension need building regulations approval?
Almost every extension does, whatever the planning position. The Planning Portal says “Most extensions of a property require approval” under the building regulations. We coordinate building regulations compliance as part of the project, so approvals are handled by the team doing the building and you receive the completion paperwork at handover.
Your neighbours are a separate question. Craig answers it in do I need to tell my neighbours? Our party wall guide covers the notices the Party Wall Act requires.
Key points
- Many single storey extensions to houses need no planning application, within the permitted development limits.
- Limits are measured from the original house, and earlier extensions and outbuildings count.
- Bigger single storey rear extensions can use the larger home extension prior approval route, outside designated land.
- Side extensions of more than one storey, flats, listed buildings and restricted properties need an application.
- A householder decision is due within eight weeks of a valid application.
- Building regulations approval is almost always needed, whatever the planning position.
Frequently asked questions
Can I extend a house that has already been extended?
Often, but the earlier work counts. Permitted development limits are measured from the original house, as built or as it stood on 1 July 1948, so a previous extension may have used some or all of the allowance. Older extensions also count towards the 50% coverage limit. Check the planning history before assuming the rights are still there.
Can I build a two storey extension without planning permission?
Sometimes, at the rear, if it extends no more than 3 metres beyond the rear wall of the original house, sits at least 7 metres from the boundary opposite, and meets the other limits. A side extension of more than one storey always needs an application, and on designated land any rear extension of more than one storey does too.
Do I need planning permission for a single storey rear extension?
Not if it stays within the limits: no more than 4 metres deep on a detached house or 3 metres on others, no more than 4 metres high, eaves no higher than 3 metres within 2 metres of a boundary, and the other conditions met. Up to 8 or 6 metres is possible through prior approval, outside designated land.
Does the 50% rule include my garden room or garage?
Yes. The 50% limit covers all buildings around the original house, existing and proposed, including outbuildings, garages and earlier extensions. Only the footprint of the original house is excluded. A garden room built last year can be the reason this year’s extension needs an application.
Is a Lawful Development Certificate worth getting for an extension?
It is not compulsory, but it gives written confirmation from the council that your extension does not need planning permission, which is useful certainty before you build and when you sell. It is most worth having when a design sits close to a limit. The official fee is half the householder fee, so £274 in England from 1 April 2026.
Talk to us about your extension
We advise on the honest planning position at the first site visit and coordinate any application as part of our design and build process. Get a quote, or call 01245 330103. We respond to every enquiry within 24 hours.