How much does a house extension cost in the UK?
A house extension costs £2,000 to £3,200 in the UK, typically around £2,500 per m². What moves the price most is floor area in square metres and single versus double storey, so a simpler job sits near the bottom of that range and a larger or higher-spec one near the top. Prices reviewed June 2026.
Extensions are priced by floor area, then by finish. A single storey extension is the common project, and the kitchen or bathroom fit-out inside it can add a lot.
House extension cost calculator
Use the calculator to price your house extension in 2026. Adjust the options and area for a UK cost range. Nothing is sent anywhere.
To price the whole job, use the extension cost calculator, loft conversion cost calculator, garage conversion cost calculator or conservatory cost calculator.
House extension cost breakdown
House extension costs £2,000 to £3,200 per m² for a standard job, so a 20 m² job comes to about £52,000. Add-ons and upgrades take it higher, up to £3,200 per m².
| What | Typical UK cost |
|---|---|
| Per m², supplied and fitted | £2,000 to £3,200 per m² |
| + Fit a kitchen in the new space | add £8,000 to £20,000 |
| 10 m² | £20,000 to £32,000 |
| 20 m² (typical) | £40,000 to £64,000 |
| 40 m² | £80,000 to £128,000 |
What's included in the price?
Typical house extension prices include:
- Foundations, structure, roof and shell
- Windows, doors and basic electrics
- Plastering and standard finish
- Building control
What changes the price?
The things that move house extension prices most:
Floor area in square metres and single versus double storey
Kitchen, bathroom or bi-fold doors inside the new space
Ground conditions and foundation depth
Finish level and any structural openings into the existing house
How the price is built up
Most builders price an extension on a rate per square metre of floor area, which is why the headline runs from 2,000 to 3,200 per m². The lower end covers a plain single storey shell with a standard finish, while 2,500 per m² is closer to what a real kitchen or living extension costs once you include foundations, a watertight roof, plastering, basic electrics and decoration. You move toward 3,200 per m² when the room carries expensive items inside it, such as a fitted kitchen, a bathroom, underfloor heating, large structural openings into the existing house, or bi-fold doors, and these are charged on top of, not within, the per m² shell figure. On a typical extension labour is roughly 55 to 65 per cent of the build cost, with materials and fixed items like windows, doors and the kitchen making up the rest, so a quote that looks cheap on materials but light on labour days is usually under-scoped.
Ways to keep the cost down
- Keep the kitchen, bathroom and any wet rooms close to existing drainage and the soil stack, because moving them adds plumbing runs and labour for no extra floor space.
- Get the ground checked early, since a sloping plot, trees nearby or made-up ground can force deeper foundations that add several thousand pounds you cannot see in a per m² rate.
- Settle the design, the kitchen layout and the door and window sizes before work starts, as changes once the builder is on site are where budgets quietly run over.
- Get at least three itemised quotes on the same drawings and specification, so you are comparing the same scope rather than a thin number against a complete one.
Does where you live change the cost?
In London, a house extension typically costs around £3,300 per m², about 30% above the UK average of £2,500. In the North, Scotland and Wales the guide figure is nearer £2,300.
| Region | From | Typical | Up to |
|---|---|---|---|
| Midlands / East (UK average) | £2,000 | £2,500 | £3,200 |
| London | £2,600 | £3,300 | £4,200 |
| South East / South West | £2,300 | £2,900 | £3,700 |
| North / Scotland / Wales | £1,800 | £2,300 | £2,900 |
Guide prices per m², scaled with the same regional multipliers as the calculator. Not quotes.
House extension cost in major UK cities
| City | From | Typical | Up to |
|---|---|---|---|
| Belfast | £1,700 | £2,100 | £2,700 |
| Birmingham | £2,000 | £2,500 | £3,100 |
| Bristol | £2,200 | £2,800 | £3,500 |
| Cardiff | £1,900 | £2,400 | £3,000 |
| Edinburgh | £2,000 | £2,500 | £3,100 |
| Glasgow | £1,800 | £2,300 | £2,900 |
| Leeds | £1,900 | £2,300 | £3,000 |
| Liverpool | £1,800 | £2,300 | £2,900 |
| London | £2,600 | £3,300 | £4,200 |
| Manchester | £1,900 | £2,400 | £3,100 |
| Newcastle | £1,800 | £2,300 | £2,900 |
| Sheffield | £1,800 | £2,300 | £2,900 |
City guide estimates, scaled by local labour costs. Indicative averages for house extension, not quotes.
In London and the South East, figures run 20 to 40 percent above the national rate per square metre.
Common questions
How much is a single storey extension?
A typical single storey extension costs around £2,000 to £3,200 per square metre for the build, so a 20 square metre extension is roughly £40,000 to £64,000 before a kitchen fit-out, with about £50,000 the typical figure at the mid rate.
Do I need planning permission for an extension?
Many single storey rear extensions are permitted development within size limits, but larger extensions, two storey work and conservation areas usually need planning permission.
How much does a double storey extension cost compared to a single storey?
A double storey extension usually costs a little less per square metre than a single storey one, often around £2,000 to £2,700 per m², because you are adding a second floor over the same foundations and roof. The total bill is still higher because you are building far more floor area. As a rough guide, doubling up on a 20 m² footprint gives you about 40 m² of space, so expect a typical figure in the region of £80,000 to £110,000 before the kitchen, bathroom and finishes inside are added.
What hidden costs should I budget for on top of the build price?
Hidden costs sit outside the per m² rate, which covers the shell and basic finish rather than the full project. Budget separately for design and drawings at roughly 7 to 15 per cent of the build, a structural engineer for any beams, building control fees, and a party wall surveyor at around £700 to £1,500 per neighbour if you build near a boundary. Large items inside the room, such as a fitted kitchen at £10,000 to £25,000 or bi-fold doors at £4,000 to £12,000, sit on top of the headline figure, and VAT applies to most extension work.
How much does a 20m2 kitchen extension cost?
A 20 m² single storey kitchen extension typically costs around £50,000 at the £2,500 per m² mid rate for the building work, then more once the kitchen itself goes in. A new fitted kitchen runs from about £10,000 to £25,000, and bi-fold or sliding doors add roughly £4,000 to £12,000 for a 3 to 4 metre span. A realistic all-in figure for a finished kitchen extension is therefore commonly in the £64,000 to £87,000 range, higher in London and the South East.
Is £30,000 enough for an extension?
£30,000 covers a small single-storey extension of roughly 9 to 15m² at a basic finish, once you allow for the £2,000 to £3,200 per m² build rate. That size suits a compact utility room, porch or study, not a large kitchen-diner. The figure usually excludes design fees, planning, structural work and any fitted kitchen or bathroom, so hold some budget back for those.
Can I build an extension for £20,000?
£20,000 stretches to a very small extension of about 6 to 10m² at a plain finish, based on the £2,000 to £3,200 per m² build rate. A modest porch, small utility or single-room addition is realistic; a kitchen or bathroom fit-out is not, since fittings, appliances and tiling sit on top of the build price. Ground conditions and any opening into the existing house can push the figure higher.
Can I build an extension myself to save money?
You can take on some of it, but not all. Labour is roughly 55 to 65 per cent of the build cost, so managing the project or doing the decorating and second-fix yourself saves a real amount at £2,000 to £3,200 per m². The catch is the structural work, which needs a structural engineer's sign-off and building control, and the groundwork and roof, which are hard to get right. Most people self-manage rather than self-build.
Does an extension add value to your house?
Often yes, more than most improvements. A well-built extension that adds a bedroom or opens up the kitchen can add value, and in many areas the uplift covers a good part of the £2,000 to £3,200 per m² build cost. It is not guaranteed to return every pound, and over-extending for the street can cap the gain, so build for how you will live in it as well as resale.
Official guidance and sources
The rules and schemes referenced on this page come from these official UK sources. The price figures are Costwise's own; see how we price.
- Planning permission: common projects Planning Portal · Many single-storey extensions are permitted development within size limits; check before you build.
- When you need planning permission GOV.UK · When a home project needs planning permission; building regulations apply either way.
These are independent guide prices based on typical UK jobs in 2026. Your actual cost depends on your property, spec, access and where you live. Always get at least three written quotes before committing.