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A single-storey kitchen extension in England typically costs £3,400 to £6,700 per m² all in, including the kitchen, fees and VAT. That means about £76k to £134k for a 20 m² room outside London and £103k to £172k in London. Use the calculator for your own size and finish.
Enter a floor area to see a range.
Headline "per m²" prices often leave out the kitchen, the fees or the VAT. We keep them apart so you can see what each figure includes. These are the rates inside the calculator, set in November 2026 from published UK price guides by builders, trade platforms and cost consultants, sitting in the middle of their ranges.
| Shell type | Outside London | London |
|---|---|---|
| Rear extension | £1,800 to £2,700 | £2,700 to £3,900 |
| Side return infill | £2,200 to £3,200 | £3,100 to £4,400 |
| Wraparound | £2,100 to £3,000 | £2,900 to £4,200 |
The shell is the finished empty room: foundations, drainage, walls, an insulated roof, one set of doors and one rooflight, steel beams to open up the back wall, wiring and plumbing, plaster, screed and paint. Side returns cost more per m² because they are narrow, run along a party wall and usually have a long glazed roof. Underfloor heating, usually £60 to £120 per m² for a wet system laid in the screed, sits inside the upper half of these ranges.
On top of the shell the calculator adds: glazing upgrades (£4k to £9k for wide sliders and a second rooflight, £10k to £25k for structural glass), the kitchen, design and structural engineering at 10 to 15% of the build, building control at £900 to £1,800, party wall surveyors at £1,000 to £3,000 per award, the statutory planning fee, a 10% contingency and 20% VAT.
Small extensions cost more per m² because the foundations, steel beam, drainage connection and fees cost almost the same at 8 m² as at 15 m². The calculator raises the shell rate by 2% for every m² below 15, up to 20%.
| New floor | Example footprint | Outside London | London | All-in per m² |
|---|---|---|---|---|
| 8 m² | 2 m × 4 m side return | £48k to £89k | £60k to £108k | £5,950 to £13,500 |
| 10 m² | 2.5 m × 4 m | £53k to £97k | £68k to £119k | £5,250 to £11,900 |
| 15 m² | 3 m × 5 m | £63k to £113k | £83k to £142k | £4,200 to £9,500 |
| 20 m² | 4 m × 5 m | £76k to £134k | £103k to £172k | £3,800 to £8,600 |
| 25 m² | 5 m × 5 m | £89k to £154k | £122k to £201k | £3,550 to £8,050 |
| 30 m² | 5 m × 6 m | £102k to £174k | £142k to £230k | £3,400 to £7,650 |
| 40 m² | wraparound size | £128k to £215k | £181k to £289k | £3,200 to £7,200 |
The low end of each range is a plain flat-roofed box with a straightforward kitchen built by a small local firm. The high end is a London-standard finish with a lot of glass and full fees. Most real quotes land in the middle third.
| Line | Low | High |
|---|---|---|
| Shell, 20 m² × £1,800 to £2,700 | £36,000 | £54,000 |
| Glazing upgrade | £4,000 | £9,000 |
| Mid-range kitchen, fitted | £12,000 | £25,000 |
| Design and engineering | £4,000 | £9,450 |
| Building control | £900 | £1,800 |
| Lawful development certificate (no VAT) | £274 | £274 |
| One party wall award | £1,000 | £3,000 |
| Contingency, 10% | £5,200 | £8,800 |
| Total before VAT, rounded | £63,000 | £111,000 |
| Total with 20% VAT, rounded | £76,000 | £134,000 |
Swap to a budget kitchen, basic glazing and no party wall award and the same room comes down to about £61k to £99k. A high-spec kitchen with the same basic glass takes it to £86k to £149k.
In London the all-in cost for a single-storey rear kitchen extension in 2026 typically runs from about £4,500 to £8,600 per m² of new floor, depending on size. A 20 m² extension with a mid-range kitchen is roughly £103k to £172k, and a 30 m² wraparound comes out higher still. The shell alone, before the kitchen, fees and VAT, is typically £2,700 to £3,900 per m² for a rear extension.
It also helps to think about how the room will be used before choosing a shape. Cooking, eating and sitting in one space changes where the island goes, where the doors go and how much light you need at the back of the house. For a practical view from a builder, see how a kitchen extension changes the way a London home is used, then come back and run the numbers here.
Many London streets sit in conservation areas or under Article 4 directions, which take away some permitted development rights. Look at your council's planning map before assuming no application is needed. Flats and maisonettes have no householder permitted development rights at all.
The kitchen is a separate budget from the building, and it is the line people most often forget when they compare per m² prices.
| Level | What you typically get | Typical cost |
|---|---|---|
| Budget | Flat-pack or trade units, laminate worktops, own-brand appliances, fitting | £6,000 to £12,000 |
| Mid | Rigid units, an island, quartz or solid wood tops, mid-range appliances | £12,000 to £25,000 |
| High | Painted in-frame or bespoke units, stone tops, premium appliances | £25,000 to £50,000 |
Units are usually about half of the kitchen figure, with worktops, appliances and fitting making up the rest. If the island is the main reason for the extension, check it fits before the walls go up with the island planner. Moving the room 300 mm wider at drawing stage costs little; finding you are 300 mm short after the build costs a lot.
You will need Building Regulations approval for practically any extension. It is separate from planning and covers structure, fire safety, insulation, ventilation and drainage. Building control from your council or an approved inspector typically costs £900 to £1,800 for a single-storey extension. LABC's homeowner guidance explains the plan check and site inspections.
Under the Town and Country Planning (General Permitted Development) (England) Order 2015, Schedule 2, Part 1, Class A, a single-storey rear extension can usually project up to 3 m from the original rear wall of an attached house, or 4 m for a detached house, without a planning application. The larger home extension prior approval raises this to 6 m and 8 m. The extension can be no taller than 4 m, and where it comes within 2 m of a boundary its eaves are capped at 3 m. A side extension must be single storey and no wider than half the original house. A wraparound counts as both, so it normally needs a householder application. The government's permitted development technical guidance has diagrams for each case.
| Route | When | Fee |
|---|---|---|
| Permitted development | Within the limits above, a house, no Article 4 | £0 |
| Lawful development certificate | Proof that the work is permitted; buyers' solicitors often ask | £274 |
| Prior approval, larger home extension | Rear extension 3 to 6 m deep (4 to 8 m detached) | £249 |
| Householder planning application | Anything outside permitted development | £548 |
| Building control | Every extension | about £900 to £1,800 |
A draft change to the fee regulations, if approved by Parliament, would raise the householder fee to £575 and the larger home extension prior approval fee to £310 from 8 December 2026. The Planning Portal fee guidance shows the fee in force on the day you apply. Applying online through the Portal adds a £75.83 plus VAT service charge; applying direct to your council avoids it. Scotland, Wales and Northern Ireland set their own fees.
Building an extension to an existing home is standard-rated: 20% VAT on labour and materials if the builder is VAT registered. A sole trader under the VAT threshold will not charge it, which is one reason quotes can differ so much. Often missing from first quotes:
Not a kitchen extension. £20,000 including VAT will pay for a mid-range kitchen refit in the existing room, or a small porch or garden room. The smallest extension in our calculator, 8 m² with a budget kitchen, basic glass and no party wall award, still comes to about £33k to £55k.
For a refurbishment, often yes: a new kitchen in the existing room, a bathroom, rewiring and decoration. For a kitchen extension plus anything else, no. Outside London, £50k covers a small 8 to 10 m² extension with a budget kitchen and plain glazing, with little left over.
Outside London, a 20 to 25 m² rear extension with a mid-range kitchen, decent glazing and full fees, with some contingency left. In London, about 15 m² on similar terms, at the lower end of the range (£83k to £142k).
For layout approaches that suit different houses, see kitchen extension ideas.