Rough cost per square metre
National guides for 2026 put the build cost of an extension, before VAT, at roughly:
- Single-storey: about £2,200 to £3,300 per m², depending on the quality of finish
- Two-storey: about £2,000 to £3,200 per m². The cost per m² is often a little lower because the foundations and roof are shared over two floors.
So a 20 m² single-storey kitchen extension might cost roughly £44,000 to £66,000 to build, before the kitchen itself, fees and VAT. These are UK-wide figures, so treat them as a guide rather than a quote.
Costs people often forget
- Design and drawings, plus a structural engineer for beams and foundations
- Planning or a Lawful Development Certificate, if needed
- Building regulations fees, typically several hundred to over a thousand pounds
- Party wall agreements if you're building on or near a shared boundary
- VAT, which is usually charged at 20% on extension work
- Kitchens, bathrooms and finishes, which can be a big part of the total
- A contingency of around 10% for anything found once work starts
What makes the biggest difference
- Size and shape. A simple rectangle is cheaper than a complicated footprint.
- Glazing. Large sliding or bifold doors and roof lanterns add cost.
- Ground conditions. Sloping North Devon gardens, drains in the way or poor ground can mean deeper foundations.
- Access. Terraces with no side access mean everything comes through the house.
- Finish. The specification of the kitchen, flooring and fittings.
Fixed-price planning and build packages
We price design, planning, building regulations and the build as one fixed package, agreed up front from a clear specification. No nasty surprises: the price only changes if you choose to change the job, and we agree any change with you first. How our packages work.
Get a real price for your extension
We'll visit, measure up and give you a clear, itemised price, and we can handle the drawings, planning and building regulations too. More on our extensions and planning and building regs service.
Quick answers
How much does a single-storey extension cost?
National 2026 guides put it at roughly £2,200 to £3,300 per m² before VAT, depending on finish, plus fees, VAT and fittings.
Do I pay VAT on an extension?
Usually yes, at 20%. Some specific cases can be lower, so check with your accountant or HMRC.
Is a two-storey extension better value?
Often, per square metre, because the foundations and roof cover two floors of space.
Talk to us about your project
Call or text any time, or email us. We're happy to pop round for a no-obligation chat.
We work within roughly 15 miles of our base in Tawstock, including Barnstaple, Bideford, Braunton, Great Torrington, South Molton, Ilfracombe, Fremington, Instow, Northam, Westward Ho!, Appledore, Bishop's Tawton, Swimbridge, Landkey, Chittlehampton, Atherington, High Bickington and Chulmleigh.