See extension costs by size from 9m² to 50m² →
What affects the cost?
Current June 2026 Checkatrade guidance places a typical house extension at about £1,800–£3,000 per square metre before VAT. Floor area is only the starting point: structural openings, steelwork, glazing, kitchens or bathrooms, access, specification and region can move a real quote materially above or below a simple area calculation.
- Floor area and number of storeys
- London and regional labour rates
- Steelwork and structural changes
- Kitchen or bathroom installation
- Glazing and door specification
- Finish level, access and contingency
Typical cost breakdown
Regional planning examples
The examples below apply our published modelling factor to the same national benchmark. They are not claimed as observed city-wide average quotes.
House extension costs by location
Open a detailed city page to see the same national benchmark adjusted through the transparent regional model, with local planning considerations and worked examples.
Sources used for this guide
House Extension: Cost Breakdown 2026
Published / checked: June 2026
Used for: Extension cost-per-m² benchmarks and common add-on costs
Construction output price indices
Published / checked: 13 August 2026
Used for: Construction price trend and update checks
Frequently asked questions
How much does a house extension cost per m² in 2026?
Current Checkatrade guidance gives a broad UK benchmark of about £1,800–£3,000 per square metre before VAT. The final rate depends on region, specification, structural work, access and what the quote includes.
How much does a 20 m² extension cost?
Multiplying the current £1,800–£3,000 per-m² benchmark gives a straight-line planning range of about £36,000–£60,000 before VAT. Small projects can cost more per square metre because fixed costs are spread over less floor area.
Are London extensions more expensive?
Often yes. Labour, access, logistics, parking and contractor overheads can push London and parts of the South East above the national benchmark, which is why postcode-aware modelling is useful.
Does the per-m² figure include a kitchen or bathroom?
Do not assume it does. A kitchen, bathroom, unusually large glazing package, complex steelwork and professional fees should be checked as explicit quote line items.
Related costs
House renovation
Current UK whole-house renovation costs with a detailed 3-bedroom benchmark covering heating, rewiring, windows, plastering, kitchen, roof and other major works.
About £76,690 for the published 3-bed benchmarkView guide →Cost guideBuild a house
UK new-build and self-build costs per square metre, by house size, specification and project complexity.
£1,400–£3,000 per m²View guide →Cost guideRSJ beam
UK RSJ steel beam supply and installation costs for openings, extensions and load-bearing wall work.
£200–£950 beam + £300–£750 installationView guide →