Cost Guide · Updated September 2026
Kitchen Extension Cost UK 2026: Single-Storey Rear Extension + Kitchen Fit-Out
A single-storey kitchen extension costs £42,000–£85,000 fully fitted in 2026 for a typical 20–30m² rear extension on a 3-bed semi, with the shell at £28k–£55k and the kitchen fit-out at £14k–£30k. This guide covers cost by size, the split between extension and kitchen, regional variation, and what the build actually delivers when the goal is one big kitchen-diner.
Get Free Quotes →Kitchen Extension Cost — UK 2026
| Extension Size | Shell Only | Fully Fitted (incl. kitchen) |
|---|---|---|
| Small (15–20m², 3m deep) | £22,000–£36,000 | £34,000–£55,000 |
| Standard (20–30m², 4–5m deep) | £28,000–£48,000 | £42,000–£72,000 |
| Large (30–45m², 6m deep) | £42,000–£68,000 | £58,000–£95,000 |
| Wrap-around (rear + side return) | £55,000–£80,000 | £72,000–£115,000 |
| Premium spec (steel-frame glazing, large rooflights, marble worktops) | Add £18,000–£40,000 over the figures above | |
Figures assume a typical 3-bed UK semi with straightforward ground conditions, no underpinning, no basement, a single-storey flat-roof build with 2–3 rooflights, bi-fold or sliding doors, knock-through to the existing rear room, and a new mid-range kitchen of £12k–£22k installed.
Last updated 2026-05-18. London & South East run 20–30% above the figures shown. Within the figures, the kitchen fit-out is typically 30–40% of total cost.
The Two-Part Quote: Extension Shell + Kitchen Fit-Out
A kitchen extension is really two projects in one. Reputable builders quote them separately so you can see where the value goes. Popular upgrades such as underfloor heating and premium worktops sit in the fit-out half:
Extension Shell (~60% of cost)
- Architect drawings & planning — £2,500–£6,500
- Structural engineer — £900–£1,800
- Building Control & Party Wall — £1,200–£4,500
- Foundations & substructure — £4,500–£12,000
- Brick / blockwork & steels — £8,500–£18,000
- Warm flat roof + rooflights — £5,500–£12,500
- Bi-fold or sliding doors — £4,500–£10,500
- Knock-through + new steel to existing — £3,500–£7,500
Kitchen Fit-Out (~40% of cost)
- Kitchen units & doors — £6,500–£16,000 (mid-range)
- Worktops — £1,800–£5,500 (quartz / granite / Dekton)
- Appliances — £2,500–£8,500
- Sink, taps, splashback — £600–£1,800
- Kitchen fitter labour — £2,200–£4,500
- Flooring (porcelain or engineered timber) — £2,500–£5,500
- Underfloor heating — £1,800–£3,800 (wet UFH for 25m²)
- Lighting, electrics, plumbing 2nd-fix — £1,800–£3,800
Tip: most builders subcontract the kitchen fit to a specialist (Wren, Howdens, Magnet, John Lewis of Hungerford). Get the kitchen designed and priced separately, then ask the builder to price the shell and the fitting only — you'll save £3k–£8k versus a single lump-sum quote.
Kitchen Extension Cost by UK Region (Standard 25m², Fully Fitted)
| Region | Typical Cost | vs UK Average |
|---|---|---|
| London | £58,000–£90,000 | +30% |
| South East | £52,000–£82,000 | +20% |
| South West | £46,000–£72,000 | +8% |
| Midlands | £42,000–£68,000 | Baseline |
| North / Yorkshire | £38,000–£60,000 | −10% |
| Wales | £40,000–£62,000 | −7% |
| Scotland | £40,000–£64,000 | −5% |
Materials are nationally priced; regional variation is driven by builder day rates, scaffold hire and kitchen-fitter labour. London & the South East are consistently 20–30% above baseline. Conservation areas or listed buildings add 10–20% nationally for planning and material constraints.
On a kitchen extension the shell is only half the budget: the fit-out of units, worktops, appliances and flooring often costs as much again as the building work, which is why two identical footprints can land thousands apart. Bi-fold or sliding doors, a roof lantern, and moving drainage or the boiler are the usual cost jumps. Size the build with our kitchen extension cost calculator, then price the kitchen itself separately with the kitchen cost calculator so neither surprises you.
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