How Much Does a House Extension Cost in Cheshire & North Wales? (2026 Prices)
The short answer
In 2026, a single-storey extension in Cheshire and North Wales typically costs £1,800–£2,800 per square metre to build. That puts a normal 20m² rear extension at roughly £40,000–£56,000, and a larger 40m² double-storey extension at around £70,000–£100,000. The North West sits below London prices - you're not paying the capital's 25–40% premium - but where you land in that range depends almost entirely on decisions you make before a single brick is laid.
Here's how to work out your number, and where the money actually goes.
What an extension costs by size
Use this as a starting budget. These are build costs for a standard-to-good specification in Cheshire and North Wales — the figure the builder charges, before fees, VAT extras and fit-out choices.
Small single-storey rear (12–15m²): £24,000–£40,000
Standard single-storey rear (20m²): £40,000–£56,000
Large single-storey or wrap-around (30m²): £55,000–£85,000
Double-storey side or rear (40m²): £70,000–£100,000
Kitchen-diner with big glazing (25–30m²): £60,000–£95,000
Why the ranges are wide: a plastered box with a radiator costs very different money to the same footprint with bi-fold doors, a roof lantern, underfloor heating and a fitted kitchen. The structure is only part of the bill.
The costs almost everyone forgets
The build cost is the number people fixate on. These are the ones that blow budgets, because they're invisible until they arrive:
Design and drawings - planning and Building Regulations drawings (typically 8–15% of build cost, or a fixed fee)
Structural engineer - steel beam calculations, usually £600–£1,500
Planning application fee - ÂŁ548 in England (from April 2026)
Building Control - inspection fees, often £500–£1,000
Party Wall agreements - if you share a wall with a neighbour, £700–£1,000+ per surveyor
Kitchens, bathrooms, flooring, decorating - the fit-out that makes it liveable, easily £10,000–£30,000
VAT - most extensions attract 20% VAT on labour and materials
A realistic total budget is often 20–30% more than the headline build cost. Anyone who tells you the build figure is the whole cost is setting you up for a nasty surprise.
What pushes the price up (and what you control)
Adds cost:
Glazing. Bi-folds, sliding doors and roof lanterns are gorgeous and expensive. A single run of quality bi-folds can be £5,000–£10,000.
Ground conditions. Trees, drains, sloping sites and poor soil all mean deeper, pricier foundations — and you often don't know until you dig.
Conservation area or listed building. More design, extra consents, higher-spec materials. Common across Chester.
Kitchens and bathrooms. Where taste meets budget fastest.
Changing your mind after work starts. The single most expensive habit in construction.
Keeps cost down:
A simple, well-proportioned shape. Clever design beats expensive materials. A well-considered plain box feels better than a badly designed complicated one.
Deciding everything before you start. Every decision made on site, in a hurry, costs more than the same decision made calmly on paper.
A single, coordinated set of drawings the builder can price accurately - which brings us to the thing that actually protects your budget.
The cheap quote that costs you the most
Here's the trap. You get three builder quotes off a basic set of planning drawings. They vary wildly - say ÂŁ42,000, ÂŁ55,000 and ÂŁ68,000 - and you've no idea why, because the drawings don't specify enough for the builders to be pricing the same extension. So each one has guessed, and padded for the risk.
You pick the cheapest. Then, mid-build, every unspecified detail becomes a "that wasn't included" conversation, and the ÂŁ42,000 quietly becomes ÂŁ58,000 - with a result you're not thrilled by.
The fix is a properly detailed set of drawings and a specification before you get quotes. When every builder prices the exact same, fully-described extension, the quotes come back close together, you can compare them honestly, and there's far less room for mid-build surprises. That detailing is the single best budget-protection money you can spend - it usually saves more than it costs.
This is exactly what a good architectural designer does, and why "just get some drawings for planning" is a false economy on anything but the simplest project.
How to budget yours in three steps
Take your footprint × the per-m² figure from the table above for a rough build cost.
Add 25% for design, fees, structural work, VAT and fit-out — your realistic all-in budget.
Hold back 10% as contingency. Every honest builder and designer will tell you to. The projects that go wrong are the ones with no slack.
If that total works for you, you're ready to talk to a designer. If it's tight, a designer can often find the same brief in a smaller, smarter footprint — which is cheaper to build and frequently better to live in.
Frequently asked questions
How much does a single-storey extension cost in Cheshire in 2026?
Expect roughly £1,800–£2,800 per square metre to build, so about £40,000–£56,000 for a standard 20m² rear extension. Add around 25% on top for design, fees, VAT and fit-out to reach a realistic all-in budget.
Is an extension cheaper in North Wales than Cheshire?
Not dramatically. Build costs across Cheshire and North Wales are broadly similar and both sit below London and the South East. Ground conditions and specification affect your price far more than which side of the border you're on.
What's the most expensive part of an extension?
Usually glazing, kitchens and groundworks. Large bi-folds and roof lanterns, a fitted kitchen, and unexpected foundation work are where budgets most often stretch. Good design manages all three before you commit.
Why do builder quotes vary so much?
Almost always because the drawings don't specify enough, so each builder is guessing at different things and pricing in different risk. A detailed drawing set and specification make quotes genuinely comparable and reduce mid-build surprises.
How much should I keep as contingency?
At least 10% of your total budget. Extensions involve unknowns - especially below ground - and a contingency is what keeps a surprise from becoming a crisis.
Thinking about an extension in Cheshire or North Wales?
Studio 9 Architecture is an architectural design studio based in Chester, working across Cheshire, North Wales and Lancashire. Before you commit to a budget, we can tell you what your ideas are realistically likely to cost - and how to get the most house for the money you have.
Start a conversation → the first chat is free, and you'll come away with a clearer number than any online calculator can give you.