Plan extension costs per square metre and understand the difference between shell-only and finished space.
Applies to: UK homeowners. Planning, Building Regulations and party-wall requirements depend on the project and location.
Last checked: 3 October 2026
Key points
• Current UK guidance puts full extension costs broadly around £1,800–£3,000 per m².
• Shell-only extensions are published around £1,200–£1,700 per m².
• A 20m² single-storey extension is currently budgeted around £40,000–£56,000 in one major guide.
• Kitchens, bathrooms and complex structural work push costs above basic living-space rates.
Getting ready to arrange the work?
Search BuildPair for tradespeople who offer the services you need. Check profiles and discuss the details before agreeing to any work.
Typical 2026 extension rates
Current UK market guidance puts full house-extension costs around £1,800–£3,000 per m², averaging about £2,400 per m², and shell-only costs around £1,200–£1,700 per m².
Example project sizes
Its 2026 guide places a 20m² single-storey extension around £40,000–£56,000, a 30m² project around £60,000–£84,000 and larger 50m² projects around £100,000–£140,000.
Budget beyond the shell
• Design and structural engineering.
• Building Control fees.
• Kitchen or bathroom fit-out.
• Glazing and doors.
• Heating and electrical work.
• Flooring and decoration.
• Contingency for ground conditions and changes.
Official sources
Use these official sources for the current detail that applies to your job, contract or location.
Further sources
Additional published guidance and research used in this article.
Pricing methodology
BuildPair reviews current UK market pricing references when preparing cost guides. Published figures are budgeting ranges, not BuildPair quotes or guaranteed local prices. Compare current local quotes before appointing a tradesperson.
BuildPair provides general information and signposting, not legal, structural, electrical, gas or building-control approval. Requirements can change and the right answer depends on the work, contract, location and facts.
Related BuildPair guides
One project. Both sides connected.
A fairer UK marketplace and project platform for homeowners and tradespeople, from first search to finished job.
BuildPair is a marketplace and project platform, not a building contractor or building-control body. See Payments, Terms and Disclaimer for full details.