Quick Answer
A house extension is one of the biggest investments you can make in your property. In 2026, a single-storey rear extension in the UK costs between £30,000 and £60,000, while a two-storey extension runs £40,000 to £90,000.Single-Storey Extension CostsThe average cost per squar...
Key Information
- Last Updated:
- 17 Apr 2026
- Category:
- Cost Guides
- Reading Time:
- 1 min read
A house extension is one of the biggest investments you can make in your property. In 2026, a single-storey rear extension in the UK costs between £30,000 and £60,000, while a two-storey extension runs £40,000 to £90,000.
Single-Storey Extension Costs
The average cost per square metre for a single-storey extension is £1,500 to £2,500. A typical 4m x 5m extension (20m²) costs £30,000 to £50,000 including foundations, walls, roof, windows, electrics, plumbing, plastering, and basic finishing.
Two-Storey Extension Costs
A two-storey extension costs roughly 50-60% more than single-storey, not double. You are reusing the same foundations and roof structure.
What Pushes Costs Up
Structural steelwork for open-plan layouts adds £2,000-5,000. Underfloor heating adds £50-80 per m². Bi-fold doors cost £3,000-7,000. Building in London adds 20-40% to labour costs.
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Just wondering if those costs include VAT? Planning to extend next year, so keen to budget accordingly. Cheers!
I'm planning a single-storey extension this year. Should I aim for the lower end of that £30k - £50k range?
I'm planning a single-storey extension in Bath. The £30k-£50k range seems about right for my 20m² space. Will need to factor in those lovely bi-fold doors!