Kitchen Extension Costs in 2026: The Real Numbers
What does a kitchen extension actually cost in 2026? We break down the numbers by size, spec, and region - with trade-by-trade detail.
A kitchen extension is one of the most popular - and most expensive - home improvement projects in the UK. But "it depends" isn't helpful when you're trying to set a budget. For a full trade-by-trade breakdown with regional adjustments, see our Kitchen Extension Cost Guide. Here are the real numbers for 2026.
Quick cost summary
For a single-storey rear kitchen extension with standard finishes:
| Size | Budget spec | Standard spec | High spec |
|---|---|---|---|
| 3m × 4m (12m²) | £28,000–£34,000 | £36,000–£44,000 | £48,000–£60,000 |
| 4m × 5m (20m²) | £42,000–£52,000 | £55,000–£68,000 | £72,000–£90,000 |
| 5m × 6m (30m²) | £58,000–£72,000 | £76,000–£95,000 | £100,000–£130,000 |
These are all-in costs for the South East (excluding London). Adjust ±15–25% for other regions.
Costs based on BCIS regional benchmarks and MyBuildAlly quote analysis, Q1 2026. Your actual costs will vary based on specification, access, and local labour rates.
Where the money goes
The kitchen extension cost splits roughly as follows:
Groundworks and foundations - 15–20%
This is your biggest variable. Strip foundations on stable ground might cost £150/m². But if you hit clay, a bad water table, or need piling, expect £250–£400/m².
Structural shell - 25–30%
Walls, roof, steelwork (if opening up to the existing house), windows and doors. A large bi-fold door run can easily add £3,000–£8,000 to this section. You'll need a structural engineer to design any steelwork, and scaffolding for the duration of the build.
First fix - 15–20%
Plumbing, electrics, and plastering before the kitchen goes in. Underfloor heating adds £50–£80/m² at this stage - much cheaper than retrofitting later. Don't forget the boiler replacement costs if your heating system needs upgrading.
Kitchen fit-out - 20–30%
The kitchen units, worktops, and appliances are where specification has the biggest impact:
| Component | Budget | Mid-range | Premium |
|---|---|---|---|
| Kitchen units (supply) | £3,000–£5,000 | £6,000–£12,000 | £15,000–£30,000+ |
| Worktops | £500–£1,200 | £1,500–£3,000 | £3,500–£8,000 |
| Appliances | £1,500–£3,000 | £3,000–£6,000 | £6,000–£15,000+ |
Second fix and decoration - 10–15%
Final plumbing connections, sockets, switches, lighting, tiling, and painting. Often underestimated - allow £3,000–£5,000 for a standard-sized extension. For decoration costs, see our painter and decorator cost guide.
Regional price differences
London and the South East command a premium. Here's how other regions compare:
| Region | Factor vs national avg |
|---|---|
| Greater London | ×1.15–1.30 |
| South East | ×1.05–1.15 |
| South West | ×0.95–1.05 |
| Midlands | ×0.90–1.00 |
| North West | ×0.85–0.95 |
| North East | ×0.80–0.90 |
| Scotland | ×0.85–0.95 |
| Wales | ×0.80–0.90 |
Hidden costs most people miss
Planning and building regs
Most single-storey rear extensions fall under permitted development, but check first. If you need a full planning application, budget £462 for the fee plus £1,000–£2,000 for architectural drawings.
Building regulations approval is mandatory either way - typically £500–£1,000.
Party wall
If your extension is within 3 metres of a neighbour's boundary (or 6 metres for deeper foundations), you'll need a party wall agreement. Budget £700–£1,500 per neighbouring property.
Temporary kitchen
You'll be without a kitchen for 8–14 weeks. Some families set up a temporary kitchen in another room. Others eat out more. Either way, factor in £500–£1,500 for the inconvenience.
How to keep costs down
- Keep the footprint simple - rectangular extensions are cheapest. Every angle adds cost. If you need extra space but don't want the cost of an extension, a garage conversion is often a more affordable alternative
- Avoid moving the soil stack - relocating drainage is expensive and disruptive
- Choose standard window sizes - bespoke glazing carries a premium
- Get the spec right first - changes mid-build are the number one budget killer. Knowing how to read a builder's quote helps you lock down the spec before work starts
- Use our free estimator - get a benchmark estimate before you approach builders so you negotiate from a position of knowledge
What about your project?
Every kitchen extension is different. If you've already got a quote, watch for signs of overcharging and check the Certificates & Inspections your project will need. Upload your builder's quote to MyBuildAlly and we'll tell you whether the price is in the right ballpark, flag any scope gaps, and give you trade-by-trade benchmarks for your specific postcode.
Sources
- BCIS Average Building Prices - regional cost benchmarks, Q1 2026
- Spon's Architects' and Builders' Price Book 2026 - material and labour rate reference
- Planning Portal - planning application fees and permitted development rules
- Analysis of residential construction quotes submitted to MyBuildAlly, January–March 2026