A single-storey extension typically costs £25,000 to £40,000 in the UK, around £1,800 per square metre, according to MyJobQuote. Where you live changes the starting point: one 2026 index puts it from £33,500 in London, £30,000 in the South East and £25,000 in the Midlands, almost entirely through labour rates.
A single-storey rear extension in the UK typically costs £25,000 to £40,000, or around £1,800 per square metre, according to MyJobQuote’s single storey extension guide. Basic finishes sit closer to £1,000 to £1,700 per square metre and a high specification at £1,900 to £2,200. Where the job is built moves the starting point, mostly through labour rates.
What an extension costs by region
| Region (as BestBuilders groups them) | "Starting from" price | Typical range |
|---|---|---|
| London | £33,500 | £33,000 to £67,000 |
| South East | £30,000 | £30,000 to £60,000 |
| Southern (Hampshire, Wiltshire, Dorset) | £27,500 | £27,000 to £55,000 |
| Eastern (East Anglia) | £27,000 | £27,000 to £54,000 |
| East and West Midlands | £25,000 | £25,000 to £50,000 |
| North West | £23,500 | £23,000 to £50,000 |
| South West | £23,000 | £23,000 to £46,000 |
| North East | £22,500 | £22,000 to £45,000 |
| South Wales, Merseyside and North Wales | £22,000 | £22,000 to £44,000 |
The pattern is consistent: London is the most expensive and the North East, Wales and the South West the cheapest, with a gap of £11,500 between the top and bottom “starting from” prices. These figures come from one vendor’s model, not from quotes: BestBuilders’ 2026 extension index says its prices are rounded, “starting from” figures built from national cost guides and a regional labour index, for budgeting rather than quoting. Other sources publish higher numbers for the same job, so treat the table as a floor.
What actually moves your quote
- Size and shape. Cost scales with floor area, so a 20 square metre room costs roughly twice a 10 square metre one before economies of scale.
- Specification. Bifold doors, rooflights, underfloor heating and a high-end kitchen add far more than the shell itself.
- Ground conditions and access. Poor ground, drainage runs to move and awkward site access all add labour.
- Building regulations and fees. Structural engineer, building control and drawings are separate from the build price. Check whether each quote includes them.
- Labour rates in your area. The regional table above is almost entirely this, since materials cost the same everywhere.
What that means in pounds, at an illustrative £1,800 per square metre
| Floor area | Rough build cost at £1,800 per m2 |
|---|---|
| 15 m2 | £27,000 |
| 20 m2 | £36,000 |
| 25 m2 | £45,000 |
That is simple arithmetic on MyJobQuote’s average rate, not a quote. A basic finish at the lower per-metre rate costs less, and a high specification costs more.
What is usually not in the build price
- Architect or designer fees and structural engineer calculations.
- Building control and planning application fees where they apply.
- Party wall costs if you build near a shared boundary.
- Kitchen units, flooring and decorating, depending on how the quote is written.
- VAT, so check whether each quote includes it.
Do you need planning permission?
Not always. Many single-storey rear extensions can go ahead under permitted development, but building regulations apply almost every time. Our guide to planning permission for a single-storey extension covers the depth, height and boundary limits.
Getting quotes you can compare
Ask three builders to price the same drawings and the same specification, and ask each to separate labour, materials, fees and a contingency. Our guide to finding a builder for your extension covers references, deposits and what a proper quote contains. To see how local builders are checked, read how we choose our Top 5.
Questions to ask each builder
- Is the price fixed, or an estimate that can move?
- What is included: drawings, engineer, building control, VAT, making good?
- How will payment be staged, and against what completed work?
- Can I see a similar extension you have finished, and speak to the owner?
- Who deals with building control inspections and sends me the completion certificate?
Frequently asked questions
How much does a single-storey extension cost?
MyJobQuote puts a typical UK single-storey rear extension at £25,000 to £40,000, or around £1,800 per square metre, with basic finishes nearer £1,000 to £1,700 per square metre and a high specification £1,900 to £2,200. Your own figure depends on size, finish and region.
Why do extensions cost more in London and the South East?
Mostly labour. Bricks, timber and roofing are priced nationally, so the regional gap comes from what builders charge per day. One 2026 index starts a standard single-storey extension at £33,500 in London against £22,000 in South Wales and Merseyside.
Do I need planning permission for an extension?
Many single-storey rear extensions fall under permitted development and need no planning application, but building regulations approval applies almost every time. Check the size limits and any Article 4 restriction before you price a design.
How many quotes should I get for an extension?
Three itemised quotes is the usual sweet spot. Ask each builder to price the same drawings and specification, and to break out labour, materials and building regulations fees so you can compare like for like.
Related guides
More cost guides guides · All builders guides
About the author
Stu Clark
Stu spent over 15 years in the trades, working as a plumber before running his own plumbing and bathroom renovation company with a team of eight. He founded Top5Trades to give homeowners the kind of shortlist and straight advice you would get from someone who has actually done the work. More about us →