Cost Guide · Updated June 2026

Kitchen Extension Cost UK 2026: Single-Storey Rear Extension + Kitchen Fit-Out

Q: What is the difference between a kitchen extension and a kitchen renovation?

A kitchen renovation replaces the kitchen within the existing footprint (7,000 to 25,000 pounds). A kitchen extension adds new floor area and fits a new kitchen, usually creating an open-plan kitchen-diner (42,000 to 85,000 pounds). The decision is whether you want more space or just a better kitchen.

Q: Do I need planning permission for a kitchen extension?

Most single-storey kitchen extensions on semis or detached homes are Permitted Development if no more than 4m deep (detached) or 3m (semi), no taller than 4m, materials match, and the property is not in a conservation area or listed. Larger Prior Approval extensions up to 6m or 8m need neighbour notification.

Q: How long does a kitchen extension take to build?

A standard 20-30 sqm kitchen extension takes 14 to 22 weeks on site after planning. Allow 4 to 8 weeks for drawings and 8 to 12 weeks for planning, or 6 weeks for a Lawful Development Certificate. Full timeline from idea to dinner in the new kitchen is 8 to 13 months.

Q: Should I get the same builder to do the extension and the kitchen?

Usually no — specialise. Get the kitchen priced separately by a specialist (Wren, Howdens, Magnet, JL of Hungerford or local independent), then ask the builder to quote shell plus install of supplied kitchen units. Saves 3,000 to 8,000 pounds versus a single lump-sum quote.

Q: Will a kitchen extension add value to my house?

Usually yes, particularly in London and the South East — a kitchen extension typically adds 60,000 to 140,000 pounds to a 3-bed semi in the South, comfortably more than build cost. Biggest uplift is one 30+ sqm open-plan kitchen-diner-family room. Outside the South, check with a local estate agent first.

Q: Do I need to move out during a kitchen extension?

You do not have to but it is the worst disruption to live through. Many homeowners stay during shell phase with a temporary kitchen in the dining room or garage, then rent for 4 to 6 weeks of plastering, flooring and kitchen install. Budget 1,500 to 4,000 pounds for temporary kitchen plus eating out.

Q: What hidden costs catch people out on kitchen extensions?

Common overruns: drains under footprint (1.5-4.5k relocation), tree roots or poor ground (4-12k engineered foundations), soil pipes or boiler flue reroutes (0.8-2.5k), spec creep on the kitchen (5-15k over budget), and consumer unit upgrade (0.8-2k). Build 12-15 percent contingency from day one.

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.

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Costs

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.

What's Included

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:

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.

Regional Variation

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.

FAQ

Frequently Asked Questions

How much does a kitchen extension cost in the UK in 2026?

A typical single-storey kitchen extension on a 3-bed UK semi costs £42,000–£72,000 fully fitted in 2026 for a 20–30m² rear extension, including a mid-range kitchen (£12k–£22k). Small extensions (15–20m²) start at £34k; large extensions (30–45m²) reach £95k. Premium spec adds £18k–£40k. London & the South East run 20–30% above these figures.

What's the difference between a kitchen extension and a kitchen renovation?

A kitchen renovation replaces the kitchen within the existing footprint — new units, worktops, appliances, flooring (£7k–£25k typically). A kitchen extension adds new floor area (single-storey rear or side-return extension) AND fits a new kitchen, usually with the goal of creating an open-plan kitchen-diner (£42k–£85k typically). The decision usually comes down to whether you want more space or just a better kitchen.

Do I need planning permission for a kitchen extension?

Most single-storey kitchen extensions on a semi-detached or detached property are Permitted Development if no more than 4m deep (detached) or 3m deep (semi), no taller than 4m, materials match the existing house, and the property is not in a conservation area or listed. Larger Prior Approval extensions up to 6m (semi) or 8m (detached) require notifying neighbours under the Larger Home Extension Scheme. Always apply for a Lawful Development Certificate (£100–£250) even when PD — it future-proofs the sale.

How long does a kitchen extension take to build?

A standard 20–30m² kitchen extension takes 14–22 weeks on site after planning is settled: 6–8 weeks for the shell (foundations, walls, roof, doors), 3–5 weeks for first-fix and plastering, and 4–6 weeks for kitchen install and second-fix finishes. Allow 4–8 weeks for architect drawings and 8–12 weeks for planning beforehand (or 6 weeks for a Lawful Development Certificate). Full timeline from idea to dinner in the new kitchen is 8–13 months.

Should I get the same builder to do the extension and the kitchen?

Usually no — specialise. Most main contractors subcontract the kitchen install anyway, marking it up 10–25%. Get the kitchen designed and priced separately by a kitchen specialist (Wren, Howdens, Magnet, John Lewis of Hungerford, or a local independent), then ask the builder to quote the shell PLUS “install your supplied kitchen units”. You save £3k–£8k versus a single lump-sum quote and get clearer accountability when things go wrong.

Will a kitchen extension add value to my house?

Usually yes, particularly in London and the South East. A well-designed kitchen extension typically adds £60,000–£140,000 to a 3-bed semi in the South, comfortably more than build cost. The valuation uplift is biggest when the result is one large open-plan kitchen-diner-family room of 30m²+ with indoor-outdoor flow via bi-fold/sliding doors. Outside the South, uplift is smaller; in some lower-value postcodes it may not exceed build cost — check with a local estate agent before committing.

Do I need to move out during a kitchen extension?

You don't have to, but kitchen extensions are the worst possible disruption to live through — no kitchen for 8–14 weeks of the build, dust everywhere, and the back of the house is open to the elements at various points. Many homeowners stay through the shell phase (with a temporary kitchen set up in the dining room or garage) and rent for the 4–6 weeks of plastering, flooring and kitchen install. Budget £1,500–£4,000 for a temporary kitchen plus eating-out costs if you stay.

What hidden costs catch people out on kitchen extensions?

The common overruns are: drains under the extension footprint (relocate £1,500–£4,500), tree roots or poor ground forcing engineered foundations (£4k–£12k), unexpected soil pipes or boiler flues that need rerouting (£800–£2,500), spec creep on the kitchen (£5k–£15k over original budget), and electrical fuse-board upgrade if the kitchen adds a high load (£800–£2,000). Build a 12–15% contingency into the budget from day one.

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