How much does a single storey extension cost in the UK?
For a standard single storey extension with a good quality finish, most homeowners pay between £1,800 and £3,000 per square metre for the build itself in 2026. That per square metre figure is the most reliable way to budget, because it scales cleanly with the size of the room you are adding.
| Project | Typical size | Rough cost (build only, before VAT and fees) |
|---|---|---|
| Small single storey extension | 15 to 20m² | £30,000 to £60,000 |
| Medium kitchen or family room extension | 20 to 30m² | £45,000 to £90,000 |
| Large single storey extension | 30m² and above | £60,000 to £115,000 |
These are build costs. VAT, professional fees, planning, building control and any kitchen or bathroom fit out sit on top, and we cover those further down. Every site is different, so treat these as a starting budget and confirm with written quotes from local builders.
Single storey extension cost per m²
The clearest way to price a single storey extension is per square metre, then adjust for finish and region. Builders quote this way because it lets you compare two projects of different sizes on the same basis. As a national guide for 2026:
| Region | Cost per m² (single storey) |
|---|---|
| North of England and Wales | £1,600 to £2,400 |
| Midlands | £1,800 to £2,800 |
| London and the South East | £2,400 to £3,800 |
To use these, measure the rough length and width of the new space, multiply them to get the area in m², then multiply that by the rate for your region. A 25m² extension in the Midlands at £2,300 per m² works out at about £57,500 for the build. The calculator does this for you and adds the extras.
Cost per m² by finish: basic, standard and premium
Finish level is one of the biggest swings in the per m² price. As a rough guide for a single storey build in 2026:
| Finish level | Cost per m² | What it usually means |
|---|---|---|
| Basic | £1,700 to £2,200 | Blockwork, warm flat roof, standard windows, painted plaster |
| Standard | £2,000 to £2,800 | Pitched or upgraded flat roof, a rooflight, decent glazed doors, underfloor heating in the new room |
| Premium | £2,900 to £3,800 | Structural glazing, large span doors, high end finishes throughout |
A basic single storey extension keeps the cost down by sticking to a simple footprint and standard materials. A premium build costs more per m² but can add more value if it suits the property and the area.
What affects the cost of a single storey extension
Two extensions of the same size can come back with very different quotes. The main things that move the price are:
| Cost driver | Effect on price |
|---|---|
| Size in m² | The single biggest factor. Larger builds cost more overall, though the price per m² often drops a little as the project grows. |
| Finish and specification | A basic build with standard fittings sits far below a premium build with bi-fold doors, underfloor heating and a fitted kitchen. |
| Extension position | A rear extension is the most straightforward. Side returns and wrap around builds carry more work tying the new roof into the existing house. |
| Region | London and the South East run 20 to 40 percent above the national average. The North, Wales and Scotland tend to sit lower. |
| Roof type | A flat roof is usually cheaper than a pitched roof of the same footprint. |
| Kitchen or bathroom fit out | A new kitchen with plumbing, gas and electrics can add £15,000 to £35,000. |
| Ground and access conditions | Poor soil, sloping plots or tight access all push up groundwork and labour. |
| Structural work | Removing walls, adding steel beams or changing the roofline adds cost. |
Labour usually accounts for around 35 to 50 percent of the total, with materials making up much of the rest.
Single storey extension cost by type
Single storey rear extension cost
A rear extension is built off the back of the house and is the most popular way to open up a kitchen or living area. It follows the standard £1,800 to £3,000 per m² range for a single storey build. A small 15 to 20m² rear extension starts around £30,000 to £45,000 in the North and £55,000 to £75,000 in London for the build. Rear extensions are also the most likely to fall under permitted development, which can save the cost and delay of a planning application. See our dedicated rear extension cost calculator for more.
Single storey side extension cost (side return)
A side extension, often a side return, fills in the narrow strip of land to the side of the house. It is common in terraced and semi detached homes, where it widens a galley kitchen into a proper family space. Side returns are usually small in footprint, often 5 to 12m², but the per m² cost can sit at the higher end of the single storey range because of the fiddly access and the extra work tying the new roof into the existing one.
Single storey wrap around extension cost
A wrap around extension combines a rear and a side extension into one L-shaped build. It gives the most ground floor space in a single project, which makes it popular for large open plan kitchen diners. Because it is bigger and more complex, it sits at the upper end of the single storey range, and the total is higher simply because of the larger footprint. Budget from the standard per m² rate and expect the overall figure to reflect the combined rear and side areas.
Single storey kitchen extension cost
A kitchen extension is a single storey build with the added cost of a fitted kitchen. The building work follows the usual per m² rates, and the units, worktops and appliances sit on top. As a guide, the fit out adds anywhere from £5,000 for a modest kitchen to £25,000 or more for a high end one, plus the plumbing, gas and electrical work. A medium 20m² kitchen extension often lands between £45,000 and £70,000 all in, depending on the specification you choose.
Flat roof vs pitched roof single storey extension cost
Roof type is a real cost swing on a single storey extension. A flat roof is usually the cheaper option, since it uses less material and less labour and goes up faster. A pitched roof costs more but suits some house styles better and can feel more in keeping with the original building. A warm flat roof with a good membrane performs well and is a common choice on modern rear extensions, while a pitched roof with a rooflight is popular where the extension needs to match a traditional home. The difference is worth budgeting for, because on a mid sized extension it can move the total by a few thousand pounds.
Small single storey extension cost
A small extension of 15 to 20m² is enough for a larger kitchen or a single family room. As a single storey build it starts around £30,000 to £45,000 in the North and Wales and £55,000 to £75,000 in London for the build, before VAT and fit out. Small extensions can carry a higher per m² rate than larger ones, because fixed costs like the roof and foundations are spread over less floor area. That is worth keeping in mind if you are comparing a small project against a bigger one on a per m² basis.
Extra costs to budget for
The per m² figure covers the build and basic finishes. These extras are usually separate:
- VAT. Most extension work is subject to VAT, so check with your builder how it applies to your quote.
- Planning permission. Many single storey extensions fall under permitted development and need no application, but limits apply. If you do need a householder application in England, the fee is £548 from 1 April 2026. The Wales and Scotland fees differ. Confirm the current figure on GOV.UK before you apply.
- Building regulations. Almost every extension must meet building regs for structure, insulation, drainage and fire safety. Inspection fees vary by council, usually £500 to £1,200.
- Professional fees. Architect and structural engineer fees are extra where drawings and calculations are needed, often 7 to 15 percent of the build cost.
- Party wall surveyor. If you build against or near a shared wall, a party wall agreement and surveyor may be required.
- Kitchen or bathroom fit out. A new kitchen can add £15,000 to £35,000.
- Contingency. Set aside 10 to 15 percent for surprises, especially in older homes.
Do I need planning permission for a single storey extension?
Not always. Many single storey rear extensions fall under permitted development and need no planning application, provided they stay within the size, height and position limits. As a general guide, single storey rear extensions up to a set depth for terraced and semi detached homes, and a greater depth for detached homes, can often be built without permission. The rules change if you are in a conservation area or an Area of Outstanding Natural Beauty, or if your home has Article 4 restrictions, in which case you may still need to apply. Always check with your local planning authority before you start.
Does a single storey extension add value?
A well designed single storey extension can add value, sometimes more than it costs to build, though this depends on your location, the finish and how well the new space works. A kitchen extension that creates a bright open plan family space tends to appeal to buyers, while an extension that eats too much garden or blocks light can work against you. As a rough guide, a good extension in the right home adds in the region of 10 to 20 percent to the value, but the figure varies widely by area, so treat it as a bonus rather than a guaranteed return.
How the calculator works
The single storey house extension calculator turns the per m² method into a single figure for your project. You choose:
- Extension position, such as rear, side return or wrap around.
- Size in m², or use the length and width helper if you do not know your area.
- Finish level, from basic through standard to premium.
- Region, since location moves the figure by 20 to 40 percent.
It then shows a low to high total for the build, the per m² rate used, and a separate line for extras like planning and building control, so the estimate stays honest rather than hiding the add ons inside one number. Enter your details at the end to save your estimate and get a copy.
For other extension types, see the main house extension cost calculator homepage, which covers double storey, two bedroom and property specific costs.
Frequently asked questions
How much does a single storey extension cost per m2?
Most single storey extensions cost £1,800 to £3,000 per m² for the build in 2026, higher in London and the South East. A 20m² extension is roughly £36,000 to £60,000 before VAT and fees.
Is a single storey extension cheaper than a two storey one?
Per square metre, a two storey extension is often a little cheaper, because the roof and foundations are shared across two floors. A single storey extension still costs less overall, since you are adding less total space.
How accurate is the calculator?
It gives a realistic budgeting range based on typical UK rates, not a fixed quote. Your final cost depends on your builder, your site and your finish, so confirm the estimate with written quotes.
Do I need planning permission for a single storey extension?
Not always. Many single storey rear extensions fall under permitted development, but size, height and position limits apply, and conservation areas have tighter rules. Check with your local planning authority before starting.
Does the estimate include VAT?
The per m² figures usually exclude VAT and fit out. The calculator shows extras separately, and you should ask your builder to confirm how VAT applies to your project.
How long does a single storey extension take to build?
Most single storey extensions take around 8 to 16 weeks on site, depending on size, finish and access. A small rear extension can be quicker, while a large wrap around with a complex roof takes longer.
Figures on this page are current UK market ranges for 2026 and are intended as a budgeting guide. Prices vary by region, specification and site conditions. Planning and building control fees are official figures that should be confirmed on GOV.UK and with your local council before you apply.