A single-storey extension is one of the most popular ways to add space and value to a home in England and Wales. In 2026, most single-storey extensions cost between £1,800 and £3,500+ per square metre, depending on the quality of finishes, the complexity of the build and where you live. This guide breaks down what you can expect to pay, what drives the price up or down, and how good drawings keep your budget under control. All figures updated for 2026.
What does a single-storey extension cost in 2026?
For a typical 20m² extension — around 4m x 5m, the classic rear kitchen extension — that per-square-metre range works out at roughly £36,000 to £70,000+. Where you land within it depends mostly on specification:
| Build quality | Cost per m² (2026) | Example (20m²) |
|---|---|---|
| Basic build | £1,800–£2,200 | £36,000–£44,000 |
| Mid-range finish | £2,200–£2,800 | £44,000–£56,000 |
| High-end | £2,800–£3,500+ | £56,000–£70,000+ |
A basic build means a simple rectangular plan, a flat or mono-pitch roof and standard windows and doors. Mid-range adds better materials and the things most families actually want — bi-fold or sliding doors, underfloor heating, a rooflight or two. High-end covers large structural glazing, vaulted ceilings and premium finishes throughout.
Two things to remember when you compare quotes: most builders quote excluding VAT, so allow for 20% on top unless your quote clearly says otherwise, and budget a further 10–20% for professional fees, surveys and a sensible contingency.
Single-storey extension costs by region
After size and specification, location is the biggest factor in what you’ll pay. Labour rates vary widely across England and Wales, so the same mid-range extension can cost very different amounts depending on where you live:
| Region | Typical cost per m² (mid-range, 2026) |
|---|---|
| London & the South East | £2,800–£3,800 |
| Midlands & East of England | £2,200–£2,800 (around the national average) |
| North of England | £1,800–£2,400 |
| Wales | £1,800–£2,400 |
In practice, London and the South East typically run 20–30% above the national average, driven by higher labour costs and tighter site access. If you’re building in Wales or the north of England, the same design and specification will usually come in noticeably cheaper — which is worth knowing before you assume a national headline figure applies to your street.
Factors affecting single-storey extension costs
Beyond region, these are the things that move the price most:
- Size and layout — bigger costs more overall, but the cost per m² usually falls as the extension grows, because expensive items like kitchens and drainage are spread over more floor area.
- Materials and finish quality — brick choice, flooring, glazing spec and kitchen fit-out are where budgets quietly grow.
- Build complexity — roof type (flat, mono-pitch, dual-pitch or hipped), structural openings into the existing house, and foundations. Poor ground conditions, drains or trees near the build can add real cost below ground.
- Location and labour rates — as the regional table shows, this alone can swing the price by a third.
- Planning and building regulations requirements — not usually a large cost in itself, but getting it wrong is expensive.
What can you do with a single-storey extension?
Most of the single-storey extensions we draw fall into a few familiar patterns:
- Expand your kitchen into a spacious kitchen-diner or family hub — by far the most popular choice.
- Add practical space: a utility room, a downstairs cloakroom, or extra storage that takes pressure off the rest of the house.
- Create a new garden room, studio or quiet workspace with a proper connection to the outside.
The best results come from designing the extension and the existing ground floor together, so the new space improves how the whole house works rather than just bolting a room on the back.
Planning permission and building regulations
Many single-storey rear extensions fall under permitted development, which means you don’t need a full planning application. But permitted development rights differ between England and Wales, and they don’t apply to every property — so it’s always worth checking your specific situation before committing to a design.
Whatever the planning route, building regulations approval is required for the build itself: structure, insulation, drainage, electrics and more. Detailed building regs drawings aren’t just a box-ticking exercise — they’re what lets builders price your project accurately instead of padding their quote to cover the unknowns.
Designing your extension with Arkiplan
Wondering about the price of a single story extension for your own home? At Arkiplan, all our drawings are done online — professionally and with your goals in mind. We start by understanding how you live and what you need the space to do, then work through layout, access from your existing rooms, roof options (flat, mono-pitch, dual-pitch or hipped), glazing for light and energy efficiency, and material choices that balance cost with quality.
Our fixed-price packages start from £1,698 (or £94/month over 3 monthly instalments, with no credit checks and no interest), covering everything from planning drawings through to building regulations drawings and structural calculations — so you know your design costs before you start, not after.
How much does it cost to build a single storey extension?
The cost to build a single-storey extension comes down to construction quality and scope. On average in 2026, expect the cost per square metre to range between £1,800 and £3,500+, with London and the South East at the top of that range and Wales and the north of England towards the bottom. Detailed building regulation plans are the single best tool for getting accurate builder quotes — they remove guesswork, which is what inflates prices.
Choosing the right builder
Once your drawings are ready, choosing the right builder matters as much as the design:
- Check they have real experience with single-storey extensions, not just general building work.
- Ask for references and, ideally, visit a recent job.
- Get at least three detailed quotes priced against the same professional drawings, so you’re comparing like with like.
Our plans help reduce confusion and make quote comparisons easier — every builder is pricing exactly the same specification.
Summary: how much does a single storey extension cost?
- In 2026, typical costs range from £1,800 to £3,500+ per m², or roughly £36,000 to £70,000+ for a 20m² extension.
- Region matters: London and the South East run 20–30% above the national average, while Wales and the north of England are typically £1,800–£2,400 per m².
- Most builder quotes exclude 20% VAT — always check.
- Planning routes differ between England and Wales; building regulations approval is needed either way.
- Detailed drawings protect your budget by getting you accurate, comparable quotes.
If you’re ready to know exactly how much a single-storey extension will cost for your home, get in touch with Arkiplan today — fixed-price drawings, done online, from £1,698.