The Short Answer
On our estimates, a single-storey kitchen extension of about 18m², opened up into the existing kitchen and fitted with a mid-range kitchen, costs about £60,500 to £94,400 including VAT. That's four bills in one: the extension (£43,200 to £57,600), the fees (£4,100 to £11,800), taking out the back wall with a steel beam (£3,250 to £5,000) and the kitchen (£10,000 to £20,000).
Prices you see quoted for "a kitchen extension" often leave out one or two of those, which is why they range so widely. Bifolds add £3,600 to £5,400; a premium kitchen can double the kitchen line.
Kitchen extension cost calculator
The extension, the opening into the house, the doors and the kitchen itself, priced as separate lines so you can see where the money goes.
Estimated total
£70,550 to £109,820
| Single-storey extension, 18m², standard | £43,200 to £57,600 |
| Design, engineer and building control | £4,100 to £11,800 |
| Opening up the back of the house (steel, making good) | £3,240 to £5,040 |
| Aluminium bifolds, up to 3m (instead of a standard door) | £3,600 to £5,400 |
| New medium kitchen, supplied and fitted | £10,000 to £20,000 |
| Contingency (10%) | £6,410 to £9,980 |
Kitchen extension cost breakdown
| Part | Typical cost (18m²) |
|---|---|
| Extension, standard finish (£2,400 to £3,200 per m²) | £43,200 to £57,600 |
| Design, structural engineer, building control | £4,100 to £11,800 |
| Opening up the back wall: steel, propping, making good | £3,250 to £5,000 |
| Mid-range kitchen, supplied and fitted | £10,000 to £20,000 |
| Aluminium bifolds up to 3m (optional) | £3,600 to £5,400 |
| Contingency (10%) | £6,100 to £9,400 |
The kitchen part
| Kitchen | Supplied and fitted |
|---|---|
| Small or budget | £5,000 to £10,000 |
| Medium (about 12 units) | £10,000 to £20,000 |
| Large or premium | £22,000 to £45,000 |
I'd order the kitchen early and decide on any island before the floor slab goes down, because power, water and drainage to an island run under the floor. More on kitchen prices on our new kitchen page.
Drains under the extension
Kitchen extensions often land on top of the drains. Approved Document H covers building over, or within 3m of the centreline of, any drain or sewer on the water company's sewer records: you consult the owner (usually the water company), the extension mustn't damage the pipe or block access to manholes, and there has to be a way to replace it. I'd check the sewer map before the design is fixed, because moving a manhole or diverting a drain adds cost.
Planning and building regulations
Most kitchen extensions are single-storey rear extensions. On a house in England, a single-storey rear extension up to 3m deep (4m detached) and 4m high is permitted development, or more through prior approval; designated areas and flats are different. The full rules and a checker are on our house extension page.
Building regulations always apply. The glazing limit catches a lot of kitchen extensions: windows, doors and rooflights over 25% of the floor area (plus the openings the extension covers) mean an energy calculation and usually better glass or more insulation elsewhere. And Approved Document F expects extract ventilation in a kitchen: a cooker hood extracting outside, or a fan.
Why other prices look lower
Prices quoted for "a kitchen extension" often cover only one or two of the four bills above. Read them as part of the bill, not the whole of it.
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Frequently asked questions
How much should I budget for a kitchen extension?
On our estimates, about £60,500 to £94,400 for an 18m² single-storey extension opened up into the house with a mid-range kitchen, including VAT and fees.
How much does a 2m kitchen extension cost?
It depends on the width. 2m deep across a house 6m wide, say, is 12m², or £28,800 to £38,400 to build on our estimates, before the fees, the steel and the kitchen.
How much does it cost to knock through for a kitchen extension?
On our estimates, about £3,250 to £5,000 to take out a wide section of the back wall with a steel beam, propping and making good.
Do I need planning permission for a kitchen extension?
Not if it's within permitted development: on a house in England, a single-storey rear extension up to 3m deep (4m detached) and 4m high, with other limits.
How long does a kitchen extension take?
Usually three to six months on site, with the kitchen fitted towards the end. I'd plan a temporary kitchen for part of that.
How we priced thisView sources (8, 4 official)
Rules come from the legislation and official guidance, read at source. Prices are our estimates: we check them against trade price data, retailer shelf prices and specialists' price lists, then build them up from their parts so the totals add up. Below are the sources behind the page; the trade price guides we only compare against aren’t listed. Where sources disagreed, we've said so. More on our method.
- OfficialApproved Document H: Drainage and waste disposal (2015 edition), GOV.UK. Checked 15 Oct 2026.
- OfficialApproved Document F: Ventilation, Volume 1 Dwellings (2021 edition; 2026 edition from 24 March 2027), GOV.UK. Checked 14 Oct 2026.
- OfficialThe Town and Country Planning (General Permitted Development) (England) Order 2015, Schedule 2 Part 1, legislation.gov.uk. Checked 16 Oct 2026.
- OfficialApproved Document L: Conservation of fuel and power, Volume 1 Dwellings (2021 edition incorporating 2023 amendments), GOV.UK. Checked 16 Oct 2026.
- Trade guideKitchen extension cost breakdown, Checkatrade. Checked 15 Oct 2026.
- Trade guideHouse extension cost breakdown, Checkatrade. Checked 15 Oct 2026.
- Trade guideLoad-bearing wall removal cost breakdown, Checkatrade. Checked 15 Oct 2026.
- Trade guideBifold door costs, Checkatrade. Checked 15 Oct 2026.
