Depending on where you are in the UK, for a straightforward extension you should allow around £1,000–£2,000/m2. But, the cost of your extension will all come down to a number of factors, including size, specification, and location.
Building a single-storey extension will cost the following per/m2:
- Basic quality: £1,000 to £1,680
- Good quality: £1,680 to £1,920
- Excellent quality: £1,920 to £2,160
Remember: Be mindful of ceiling prices in your area — you’ll want to make a return on the money you spend on an extension so make sure the numbers add up.
Building a two-storey extension will not cost much more per square metre because, aside from the extra interior fixtures and finishes, you are only adding walls and floor joists — a roof and foundations are required whether your extension is single or two storey.