Cost guide
How much does a house extension cost?
The published UK per-m² rate for a single-storey extension, and what actually moves it.
Our own rates for a single-storey house extension run £1,600-£3,500 per m² excluding VAT, depending on specification tier - use the cost calculator for an estimate based on your project. For general UK market context, extensions typically cost £1,800-£3,000 per m², according to HomeOwners Alliance and Checkatrade - so a 20m² extension runs roughly £40,000-£56,000, a 30m² extension £60,000-£84,000, and a 50m² extension £100,000-£140,000.
Last updated 17 August 2026
| Range | ||
|---|---|---|
| Our rate (all specification tiers) - our confirmed rate, excl. VAT | £1,600-£3,500 | Per m² |
| General market rate | £1,800-£3,000 | Per m² |
| 20m² extension | £40,000-£56,000 | Total project |
| 30m² extension | £60,000-£84,000 | Total project |
| 50m² extension | £100,000-£140,000 | Total project |
Sources: HomeOwners Alliance (2026 guide), Checkatrade (updated June 2026, figures exclude VAT), Federation of Master Builders (UK average, no date shown on source page)
Worth knowing
The market ranges below are general UK industry figures, shown for comparison. Use the cost calculator for a personalised estimate based on our own current rates.
These are general UK ranges. We build across the North West, including Darwen, Blackburn and the wider Lancashire and Greater Manchester area - site access, local trade rates and travel distance can move your actual price within (or occasionally outside) the range above.
Key points
- Roof design - a simple flat roof generally costs less than a more complex roofline.
- The number of structural openings, and glazing specification.
- Ground conditions, drainage and site access.
- Whether services (electrics, plumbing) need extending into the new space.
- Region - costs run higher in London and the South East than the UK average quoted here.
These are general published ranges, not a quote. Get an estimate based on your own project.
Start Your ProjectWant a price based on our own rates, not a market average? Take the cost calculator quiz →
Want to understand what drives this cost, not just the numbers? Read what drives the cost of a house extension? →
Looking at how much does a house extension cost?? See how we approach it →
Common questions
How much does a house extension cost? FAQs
Is this a fixed quote for my house extension?
No. The figures above are published UK industry ranges from HomeOwners Alliance and Checkatrade and Federation of Master Builders, not a quote for your project. An accurate price depends on a site survey and your specific requirements - get in touch for an estimate based on your own project.
What actually drives the price up or down?
Roof design - a simple flat roof generally costs less than a more complex roofline. The number of structural openings, and glazing specification.
What's a typical our rate (all specification tiers) in per m² terms?
Our rate (all specification tiers) typically runs £1,600-£3,500 (per m²), for a our confirmed rate, excl. VAT, based on the sources cited above.
Other cost guides
More published cost ranges
How much does a two storey extension cost?
Published per-m² rates by build quality, and what a typical two-storey extension runs in total.
What's the cost per square metre for an extension?
The per-m² method explained, and the published UK rate.
How much does planning permission cost?
The current government application fee, and what else typically adds to the cost.
Ready to make more of your home?
Tell us what you're thinking and let's see what's possible.
Start Your ProjectMore Space, Built to Last.