House extension cost in the UK (2026 guide)
Published guides put a single-storey extension at roughly £1,800 to £3,500 per square metre in 2026, before VAT, fees and fit-out. Double-storey rates per square metre tend to run lower, because the foundations and roof serve two floors, but the total bill is larger. London and the South East cost more.
The guides disagree, so use the numbers as a benchmark. Get itemised quotes for your own project.
House extension cost at a glance
| Type | Rough cost per m² | Source note |
|---|---|---|
| Single storey, finished build | £1,800 to £3,500 | Whito, Bookabuilder |
| Single storey, shell only | £1,200 to £1,700 | Checkatrade |
| Double storey | About £1,500 to £3,000 | MyJobQuote, Bookabuilder, HomeOwners Alliance |
| London single storey | £2,300 to £3,400 | Whito |
Checkatrade’s examples for a standard quality build are £60,000 to £84,000 for a 30 m² single-storey extension, and £108,000 to £180,000 for a 60 m² two-storey one.
What the per-metre price leaves out
The per-square-metre figure covers the structure only. A real budget needs more lines. Ask each builder whether their quote includes them.
- VAT at 20% on most building work.
- Professional fees for design, planning and structural engineering.
- A kitchen or bathroom. One guide adds £5,000 to £15,000 for a fitted kitchen and £4,500 to £9,000 for a family bathroom.
- Glazing, flooring and decoration.
- Landscaping and making good outside.
Single or double storey?
A double-storey extension costs more overall, since it adds more space. MyJobQuote suggests that, with equal floor areas, it costs roughly 50% to 75% more than a single storey. The cost per square metre is lower, so it often gives better value if you need the room.
Rules to check first
Planning permission is not always needed, because many single-storey rear extensions fall under permitted development in England. Check with your council, since limits apply. Most extensions need Building Regulations approval. In England and Wales, the Party Wall Act may apply if you build near a shared wall. In Scotland you may need a building warrant.
What changes the price
- Location. London and the South East add roughly 20% to 25%.
- Site access. A tight terrace costs more per square metre.
- Ground conditions. Poor ground needs deeper foundations.
- Finish. High-end finishes and large glazed doors add up.
- Complexity. Steel beams and flat roof lights add cost.
How to save
Compare at least three itemised quotes. Keep the shape simple, because every corner adds cost. Fix your design before the builder starts, since changes during the job are dear. Use our list of questions to ask a builder and read how to compare in our article on builder quotes explained.
Getting quotes
To compare, send us your job and we will pass it to local builders. We do not vet them, so check each builder with our guide to finding a tradesman you can trust. You can also read about builders near you.
Where these figures come from
We checked Whito, Bookabuilder, MyJobQuote, Checkatrade and Homebuilding in October 2026. Several are contractor or lead-generation sites, and their numbers do not agree. We show overlapping ranges and name outliers.
Frequently asked questions
How much does a house extension cost in 2026?
For a single-storey extension, guides suggest roughly £1,800 to £3,500 per square metre before VAT and fees. A 30 m² build can therefore cost £60,000 or more.
Is a double-storey extension better value?
Per square metre, often yes. In total it costs more, so it suits you if you need the extra space.
Do I need planning permission for an extension?
Not always. Many single-storey rear extensions count as permitted development in England, but limits apply. Check with your council.
Does the price include a kitchen?
Usually not. A fitted kitchen usually sits on a separate line, so ask each builder.