How much does a house extension cost in the UK?
A house extension costs £2,000 to £3,200 per m² in the UK, typically around £2,500. 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.
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.
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.
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 £50,000.
| What | Typical UK cost |
|---|---|
| Per m², supplied and fitted | £2,000 to £3,200 per m² |
| + Fit a kitchen in the new space | add £10,000 to £25,000 |
| 10 m² | £20,000 to £32,000 |
| 20 m² (typical) | £40,000 to £64,000 |
| 40 m² | £80,000 to £128,000 |
House extension cost by size
Builders price an extension per square metre of floor area, so these totals are this guide's rates multiplied out. A two storey extension counts the footprint twice, at the lower two storey rate.
| Size | Single storey | Two storey |
|---|---|---|
| 3m by 3m9 m², utility room or study | £18,000 to £29,000 | £36,000 to £48,500 |
| 3m by 4m12 m² | £24,000 to £38,500 | £48,000 to £65,000 |
| 4m by 4m16 m² | £32,000 to £51,000 | £64,000 to £86,500 |
| 5m by 4m20 m², kitchen extension | £40,000 to £64,000 | £80,000 to £108,000 |
| 6m by 4m24 m² | £48,000 to £77,000 | £96,000 to £129,500 |
| 6m by 5m30 m² | £60,000 to £96,000 | £120,000 to £162,000 |
Build only, at this guide's per m² rates: foundations, structure, roof, windows, doors, basic electrics and plastering. Building control fees, a kitchen, design fees and a party wall surveyor are on top. UK averages, including VAT, not quotes.
Building control fees by council
Most councils set their own building control charges. These are the building notice charges, including VAT, in each council's band for a single-storey extension of about 25 m². Of the 39 councils below, the building notice charge runs from £661.20 to £1,875.55, and 20 of them charge £846.77 or less.
| Council | Building notice |
|---|---|
| BoltonOne charge for any single-storey extension. | £764.40 |
| Bristol | £700 |
| BuryRevised charges from March 2026. | £856 |
| Camden (London)Any extension in its band, including basements. | £1,875.55 |
| Cheshire West and Chester | £846.77 |
| Coventry | £750 |
| Cumberland | £711.60 |
| DudleyFrom a document titled proposed charges for 2025. | £720 |
| Enfield (London) | £1,112 |
| Gateshead | £965.35 |
| Havering (London) | £859 |
| Hounslow (London) | £1,240 |
| KirkleesThe council says charges are to rise from May 2026. | £737.19 |
| Knowsley | £848.40 |
| Lambeth (London)Charges from April 2024, which the council says apply until further notice. | £997.18 |
| LeicesterCharges from August 2025. | £780 |
| Lewisham (London)Single-storey extension with no other alterations; no floor-area bands. | £1,500 |
| LiverpoolIts band also covers two-storey extensions; no date on the schedule. | £828 |
| LutonOne band for any single-storey extension under 100 m². | £1,290 |
| Milton KeynesNo date on the schedule. | £922.80 |
| Newcastle upon Tyne | £846 |
| NorthumberlandFor an extension under 30 m². | £780 |
| NottinghamCharges from April 2025. | £802 |
| PlymouthFor an extension of 15 to 40 m²; no date on the schedule. | £1,203 |
| Redbridge (London) | £1,320 |
| RotherhamCharges from April 2025. | £840 |
| Sandwell | £844.78 |
| SheffieldNo date on the schedule. | £661.20 |
| Solihull | £830 |
| South TynesideNo date on the schedule. | £1,005 |
| Southwark (London) | £1,472.76 |
| StockportNo date on the schedule. | £1,470 |
| Sutton (London) | £1,260 |
| Tameside | £892.72 |
| Tower Hamlets (London)No date on the schedule. | £1,551.60 |
| Walsall | £805 |
| West Northamptonshire | £720 |
| Westmorland and FurnessNo date on the schedule. | £696 |
| WiltshireIts band runs from 20 to 40 m² and covers loft conversions too. | £755 |
From each council's own website, checked October 2026. Bands differ between councils, so the note says where a council's is unusual. A full plans application is usually split into a plan charge and an inspection charge instead. A registered building control approver can be used instead of the council and quotes separately. Most councils set new charges each April.
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
- Work built to pass building control inspection
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 with a higher specification and harder structure, such as underfloor heating or large structural openings into the existing house. A fitted kitchen, a bathroom's fittings and bi-fold doors are charged on top of the per m² shell figure, not within it. 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.
Build a whole-project budget for a 20 m² extension
The base £2,000 to £3,200 per m² rate gives £40,000 to £64,000 for a 20 m² build. Selecting the £10,000 to £25,000 kitchen option gives £50,000 to £89,000 for build plus kitchen. Neither figure is a complete professional-fees or exceptional-groundworks budget.
For a budgeting illustration, a £50,000 build and £15,000 kitchen total £65,000 before separate items. Add the actual quotes for drawings, engineering, building-control fees, any required planning or party-wall work, and specification upgrades. Record temporary accommodation and a contingency separately. An unknown item is still a cost to resolve, not zero.
These guide figures include VAT where applicable. Check each supplier’s VAT wording before comparing quotes and do not add VAT twice. The kitchen option should only be added if that work is outside the builder’s base quote; standard doors and premium glazing also need an explicit boundary.
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 £3,000 per m², about 20% above the UK average of £2,500. In the North, Scotland and Wales the guide figure is nearer £2,400.
| Region | From | Typical | Up to |
|---|---|---|---|
| Midlands / East (UK average) | £2,000 | £2,500 | £3,200 |
| London | £2,400 | £3,000 | £3,800 |
| South East / South West | £2,100 | £2,600 | £3,400 |
| North / Scotland / Wales | £1,900 | £2,400 | £3,100 |
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 | £1,900 | £2,400 | £3,000 |
| Birmingham | £2,000 | £2,500 | £3,200 |
| Bristol | £2,100 | £2,600 | £3,400 |
| Cardiff | £1,900 | £2,400 | £3,100 |
| Edinburgh | £1,900 | £2,400 | £3,100 |
| Glasgow | £1,900 | £2,400 | £3,100 |
| Leeds | £1,900 | £2,400 | £3,100 |
| Liverpool | £1,900 | £2,400 | £3,100 |
| London | £2,400 | £3,000 | £3,800 |
| Manchester | £1,900 | £2,400 | £3,100 |
| Newcastle | £1,900 | £2,400 | £3,100 |
| Sheffield | £1,900 | £2,400 | £3,100 |
City guide estimates, scaled by local labour costs. Indicative averages for house extension, not quotes.
In London and the South East, figures run above the national rate per square metre, on labour, access and waste disposal.
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 £80,000 to £108,000 before the kitchen, bathroom and finishes inside are added.
What hidden costs should I budget for on top of the build price?
Some costs sit outside the per m² rate, which covers the shell and a 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 of about £650 to £1,300 for a single storey extension, and a party wall surveyor at around £700 to £1,500 per neighbour if you build near a boundary. In London it runs higher, up to £1,875.55 for a building notice in Camden; the council table on this page lists the charges. 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, also sit on top of the headline figure. The figures on this page already include VAT, which applies to most extension work, so do not add it again.
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. The build, the kitchen and the doors together therefore come to about £64,000 to £87,000, higher in London and the South East, before design fees, building control, a structural engineer and any party wall surveyor.
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.
Cite this data
These figures are free to use in articles, reports and research under a CC BY 4.0 licence. All we ask is a credit to Costwise, and online a link. Where your style allows, please make "Costwise" the linked word so readers can check the figure for their own region.
Costwise (2026): A house extension typically costs £2,500 per m² in the UK, ranging from £2,000 to £3,200 per m². Reviewed June 2026. costwiseuk.co.ukSource: Costwise (costwiseuk.co.uk)Costwise (2026). House extension cost. Costwise UK cost data, version 2026-10-23. https://costwiseuk.co.uk/house-extension-cost/2026-10-23 (158 jobs)Dataset DOI: 10.5281/zenodo.21159943 · also on Kaggle, Hugging Face and Figshare. Method: how we price. Downloadable CSV.
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.