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:
- 6 Jun 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.
Leave a Comment
Share your experience or ask a question about this article.
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!
I noticed you've given a range of £30,000 to £60,000 for single-storey extensions. That's quite broad - could you clarify what might push it towards the higher end?
I'm planning a single-storey extension this year. Any tips on how to keep costs under £30k? Thanks!
Just a note, when planning your 2026 extension budget, don't forget to factor in around £5/m² for VAT. It can creep up on you!
I'm planning an extension in Bristol. The cost range seems about right, but I'll keep an eye on those London labour costs!
I'm planning a single-storey extension in Birmingham. Using your £1,500-£2,500/m² estimate, that's around £37,500 to £62,500 for my 25m² space. Not cheap, but worth it!
Just to clarify, the 2026 costs mentioned are inclusive of VAT. As professionals, let's ensure we're transparent about this upfront.
I'm planning a single-storey extension in York. The £30k-£50k range seems accurate based on my research. I'll need to factor in structural steelwork for an open-plan layout - any tips on that?
I'm planning a single-storey extension in Bristol. The £30k-£50k estimate seems feasible for my 20m² space. Thinking about underfloor heating too, but I'll need to budget wisely!