A kitchen extension in 2026 costs between £25,000 and £60,000+ total. The building work runs £1,800–£2,800 per m², and the kitchen fit-out is a separate cost on top — from £5,000 for budget units up to £20,000+ for a premium kitchen with stone worktops and integrated appliances.
Kitchen Extension Costs at a Glance
Small Kitchen Extension
12–15m² · Basic spec build + budget kitchen (£5K). Flat roof, standard windows, basic electrics. Functional but no frills.
Mid-Range Kitchen-Diner
18–25m² · Good spec build + mid-range kitchen (£10–15K). Bi-fold doors, underfloor heating, quartz worktops.
Premium Open-Plan
25–35m² · High spec build + premium kitchen (£20K+). Structural glazing, vaulted ceiling, bespoke cabinetry, full island.
What Makes Up the Cost
Building Work: £1,800–£2,800/m²
This is the structural shell — everything from digging foundations to plastering walls. Your builder handles this and it covers groundwork, blockwork, steelwork, roof, windows, doors, electrics first and second fix, plumbing first fix, plastering, and decoration. On a typical 20m² kitchen extension, the building work alone runs £36,000–£56,000.
The per-metre cost for a kitchen extension tends to sit at the higher end compared to a standard rear extension because you're running more services. A kitchen needs dedicated circuits for the oven and hob, multiple socket runs, water supply and waste for the sink and dishwasher, gas supply if you're running a gas hob, and extraction ducting. That's significantly more first-fix plumbing and electrics than a living room extension.
Kitchen Fit-Out: £5,000–£20,000+
The kitchen itself is almost always priced separately from the building work. This is where costs vary massively depending on your taste and budget:
- Budget kitchen (£5,000–£7,000): Flat-pack or rigid units from the likes of Howdens or IKEA. Laminate worktops, basic handles, integrated oven and hob. Perfectly functional — plenty of people live happily with a £5K kitchen.
- Mid-range kitchen (£10,000–£15,000): Shaker-style or handleless units, quartz or granite worktops, soft-close everything, integrated dishwasher and fridge-freezer, decent extractor hood. This is where most people land.
- Premium kitchen (£20,000–£35,000+): Bespoke or high-end brands (Tom Howley, Roundhouse, Neptune). Solid surface or natural stone worktops, boiling water tap, wine cooler, full-height larder units, island with seating. The kitchen becomes the centrepiece.
Bi-Fold and Sliding Doors
Almost every kitchen extension includes large glazed doors opening onto the garden. This is often the single biggest line item after the kitchen itself:
- 3-panel bi-fold doors (2.4m wide): £2,500–£4,000 in standard aluminium
- 4-panel bi-fold doors (3.2m wide): £4,000–£6,500
- 5-panel bi-fold doors (4m wide): £5,000–£8,500
- Large sliding doors (2–3 panels): £3,000–£7,000 — cleaner sightlines, fewer moving parts
- Premium slim-frame systems (Schüco, Origin): Add 30–50% over standard aluminium
Kitchen Island
If your extension is wide enough (ideally 4m+ clear width), a kitchen island transforms the space. Budget £2,000–£5,000 for a basic island with storage, or £5,000–£12,000+ for an island with integrated sink or hob, waterfall worktop ends, and seating. The plumbing and electrics for an island add £500–£1,500 to the building work because services need to be run under the floor slab.
Additional Costs Inside the Kitchen Extension
- Underfloor heating: £50–£70/m² for water-based UFH laid before the screed. Electric UFH is cheaper at £30–£50/m² but costs more to run. On a 20m² extension, budget £1,000–£1,400.
- Utility relocation: Moving the boiler costs £1,500–£3,000. Relocating the gas meter: £400–£800 (contact your gas supplier). Moving the electrical consumer unit: £400–£700.
- Roof lantern or skylight: A 1m × 1.5m rooflight costs £800–£1,500 installed. A full roof lantern (1.5m × 2m) runs £2,500–£5,000. These make a huge difference in kitchen extensions with flat roofs.
- Extraction and ventilation: A ducted extractor hood or downdraft costs £300–£1,500 for the unit, plus £200–£600 for ducting through the wall or roof.
- Flooring: Porcelain tiles (the most popular for kitchen extensions): £40–£80/m² supplied and fitted. Engineered wood: £50–£80/m². Polished concrete: £80–£130/m².
Regional Pricing (Building Work Per m²)
Kitchen extension building costs vary significantly across the UK. London commands a 30–40% premium over the North due to higher labour rates, material delivery costs, and general demand. These figures cover the building work only — kitchen fit-out costs are broadly similar nationwide.
What Affects the Price
Size of the extension
The biggest single variable. A 12m² galley-style kitchen extension costs roughly half what a 25m² open-plan kitchen-diner does. But the per-m² rate actually drops slightly on larger extensions because fixed costs (steelwork, drainage, setup) are spread across more floor area.
Kitchen specification
A £5K IKEA kitchen vs a £30K bespoke kitchen changes the total project cost by £25,000. Worktops alone range from £500 (laminate) to £5,000+ (natural stone or Dekton). This is the area where you have most control over your budget.
Drainage and soil stack
If the extension sits over existing drains, you'll need diversions (£1,500–£3,500). Moving the soil stack — common on rear extensions — costs £2,000–£4,000. A build-over agreement with the water company is free but takes 6–8 weeks.
Foundation conditions
Standard strip foundations run £150–£200 per linear metre. Near mature trees on clay soil, you may need piled foundations at £1,500–£3,000 per pile. A trial hole (£300–£500) beforehand tells you what you're dealing with.
Steelwork requirements
Opening up the existing rear wall for a wide kitchen-diner needs steel beams. A single RSJ costs £800–£2,500 installed. Wide openings (4m+) may need paired steels or a goalpost frame, pushing to £3,000–£6,000.
Glazing choices
Standard casement windows: £400–£800 each. Bi-fold doors: £2,500–£8,500 depending on width. Large sliding doors: £3,000–£7,000. A full-width structural glass wall can cost £10,000–£20,000. The glazing specification can swing your total by tens of thousands.
Heating system
Extending your existing central heating with radiators: £800–£1,500. Underfloor heating (water-based) on a 20m² extension: £1,000–£1,400. If your boiler doesn't have spare capacity, a boiler upgrade adds £2,500–£4,500.
Roof type and rooflights
Flat roof (EPDM or GRP): cheapest at £80–£120/m². Pitched tile roof: £120–£180/m². Adding a roof lantern (£2,500–£5,000) or multiple flat rooflights (£800–£1,500 each) adds natural light but pushes costs up.
Utility relocation
Boiler relocation: £1,500–£3,000. Gas meter move: £400–£800 (your gas network operator handles this). Electricity meter move: £300–£600. If your extension blocks existing services, these aren't optional.
Site access
If materials can only access through the house (no side gate), expect a £2,000–£5,000 premium for the extra labour and mess. A concrete pump for foundations through restricted access adds £400–£800.
How to Save Money on a Kitchen Extension
💡 Practical ways to cut costs without cutting corners
- Design around the existing drainage. Don't move the soil stack unless you absolutely must. Designing the kitchen layout around existing waste positions saves £2,000–£4,000.
- Buy the kitchen yourself. Builders typically add 15–25% markup on kitchen supply. Buying directly from Howdens, Wren, or IKEA — and paying a separate kitchen fitter — often saves £1,500–£3,000 on a mid-range kitchen.
- Choose a flat roof. Unless you specifically want a pitched roof for aesthetics, a flat EPDM roof costs 30–40% less and is faster to install. A roof lantern on a flat roof actually gives better natural light than a pitched roof with Velux windows.
- Stick to standard bi-fold sizes. A 3-panel, 2.4m set is a standard size — priced much lower than bespoke widths. Going from 3 panels to 5 panels can double the door cost.
- Skip the island if you're tight on budget. A peninsula (attached to the wall on one side) gives similar functionality without running services under the slab — saving £500–£1,500 on plumbing and electrics.
- Build in the off-season. November to February is quieter for most builders. You may get 5–10% off the build cost, and trades are more available so the job moves faster.
- Avoid mid-project changes. Adding a skylight after the roof is on costs 2–3× what it would have cost in the original plan. Finalise every detail before breaking ground.
- Get at least three itemised quotes. Don't compare bottom-line numbers — compare line items. One builder might include decoration and another might not. Like-for-like comparison saves you from nasty surprises.
What Should Be in a Builder's Quote
A proper builder's quote for a kitchen extension should cover the shell and first-fix services. Make sure each quote you receive includes:
- Bathroom Tiling and foundations — excavation, concrete, damp-proof membrane, drainage connections or diversions
- Structural work — blockwork walls, steel beams, lintels, padstones, wall ties
- Roof structure and covering — joists, insulation, EPDM/GRP or tiles, fascias and soffits
- External doors and windows — bi-folds or sliders, any fixed glazing or rooflights
- First and second fix electrics — dedicated oven/hob circuits, socket runs, lighting, consumer unit upgrade if needed
- First and second fix plumbing — hot and cold supply for the sink, waste runs, dishwasher connection, heating extension
- Gas supply — pipe run to the new hob position (if gas)
- Plastering — walls and ceiling, ready for paint
- Decoration — mist coat and two coats emulsion (often excluded — ask)
- Floor screed or preparation — ready for your chosen flooring
- Scaffolding, skip hire, and waste removal
Commonly excluded: The kitchen itself (units, worktops, appliances), kitchen fitting, flooring, tiling, garden reinstatement, and building regs fees. These are usually separate contracts. Always ask what's in and what's out.
Hidden Costs to Budget For
Building Regulations
Full plans application. Every kitchen extension needs building regs sign-off. Some builders include the fee, many don't.
Structural Engineer
Beam calculations, foundation design, structural drawings. You need these before your builder can start and for building regs approval.
Architectural Drawings
Planning and building regs drawings. A kitchen extension with a simple layout sits at the lower end. Complex open-plan designs cost more.
Party Wall Agreement
Required if building within 3m of a neighbouring wall (6m for deep foundations). Your neighbour can appoint their own surveyor — at your expense.
Kitchen Fitting
If the kitchen isn't included in your builder's scope, a specialist kitchen fitter charges £150–£250/day. A mid-range kitchen takes 5–10 days to fit.
Garden Reinstatement
New patio, fencing, turf, drainage. The garden takes a battering during any extension build — budget for putting it right afterwards.
Frequently Asked Questions
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