How Much Does a Kitchen Extension Cost in 2026? The Honest Answer

A kitchen extension is consistently one of the highest-value home improvements you can make — both in terms of usable living space and property resale value. But the cost variation is enormous, and most online guides give ranges so wide they're nearly useless.

We've analysed 650+ kitchen extension jobs completed through TradeMatch in 2025–26 to give you the most accurate pricing data available.

Average kitchen extension costs in 2026

Here's what our data shows for a single-storey rear kitchen extension, fully finished including kitchen fit:

• Small (up to 15m²): £28,000 – £42,000
• Medium (15–25m²): £42,000 – £68,000
• Large (25–40m²): £65,000 – £110,000+

These figures include groundwork, structure, glazing, roofing, internal fit-out, plastering, electrics, plumbing, and a mid-range kitchen. They exclude landscaping, furniture, and high-spec finishes.

What drives the cost up

The biggest cost variable is specification. A flat-roof extension with standard bi-fold doors costs significantly less than a lantern-roof orangery with structural glass walls. The difference on a 20m² footprint can easily be £20,000–£35,000.

Other major cost factors: steel beams (required when removing a loadbearing wall — budget £1,500–£4,000 for the beam plus installation), underfloor heating (£1,200–£2,500 for a 20m² room), and glazing quality (budget units vs. triple-glazed aluminium systems).

Regional price differences

Labour rates vary significantly by location. Our 2026 data shows:

• London: Add 30–45% to national average
• South East: Add 15–25%
• Midlands / North West: At or slightly below national average
• Scotland / Wales: 5–15% below national average

What planning permission adds

Most single-storey rear extensions fall under permitted development — meaning no planning application needed. However, if your extension exceeds 4m in depth (detached house) or 3m (semi/terraced), or you're in a conservation area, you'll need full planning permission. Budget £200–£300 for the application plus 8–12 weeks of waiting time.

Getting the best value

The most effective way to control costs is to fix your specification before getting quotes. Builders can't price accurately against a vague brief — and scope creep mid-project is the single biggest driver of final bills exceeding estimates.

Get a minimum of three quotes. On TradeMatch, all quotes come from verified builders with verified reviews, and our standardised quoting format makes direct comparison straightforward. Start your kitchen extension project here.