How much does a house extension cost in the UK?

A house extension in the UK typically costs about £30,000 to £140,000 for a single-storey extension, and about £108,000 to £180,000 for a double-storey extension, depending on size, specification, and complexity. Checkatrade’s current guide gives those broad project ranges, while Homebuilding’s 2026 guide puts single-storey build costs at about £2,200–£3,300 per m² excluding VAT.

For many homeowners, the most useful way to budget is by square metre. A sensible planning rule is that a standard single-storey extension often lands around £2,200–£3,300 per m², with higher-end projects and London jobs costing more.

Typical house extension cost in the UK

Single-storey extension: around £30,000–£140,000
Double-storey extension: around £108,000–£180,000
Single-storey build rate: around £2,200–£3,300 per m² excluding VAT
Typical 30m² single-storey extension: around £66,000–£99,000 plus VAT

Cost breakdown

A house extension budget may include:

groundworks and foundations
walls, roof, windows and doors
insulation and plastering
plumbing and electrics
flooring and decorating
design fees
structural engineer fees
planning and building regulations costs
VAT in many cases

For double-storey work, Checkatrade’s current guide gives these example build rates:

standard quality: about £1,650–£2,150 per m²
good quality: about £1,830–£2,350 per m²
excellent quality: about £2,150–£3,000 per m².

What affects the price?

Several things can push the cost up or down:

Size — bigger extensions cost more overall.
Number of storeys — double-storey extensions usually cost more overall, even if they can be more efficient per m² in some cases.
Specification — better finishes, glazing, doors and fittings increase the total.
Location — London and the South East are often more expensive.
Design complexity — steels, awkward shapes, large openings and structural alterations can raise costs.
Professional fees — architects, drawings, structural engineering and approvals all add to the budget. Homebuilding notes architect fees commonly run as a percentage of construction cost, and building regulations fees can be substantial too.

What’s usually included?

A standard extension quote may include:

shell construction
roof
windows and external doors
insulation
plastering
first-fix and second-fix basics
standard labour.

It does not always include:

kitchen or bathroom fit-out
flooring and decorating
landscaping
planning drawings
structural engineer fees
building regulations fees
VAT
contingency for hidden issues.

Is a single-storey or double-storey extension cheaper?

A single-storey extension is cheaper overall, but a double-storey extension can sometimes offer better value per square metre because the roof and foundations are shared across two levels. Current Homebuilding and Checkatrade guidance supports comparing both total project cost and cost per m² rather than just headline price.

Do extension costs include VAT?

Not always. Homebuilding’s 2026 single-storey m² figures are stated excluding VAT, so homeowners need to be careful when comparing quotes.

Is it worth building an extension?

Often, yes, if you need more space and want to avoid moving costs. But extensions are major building projects, and Which? notes that current UK pricing data shows they require a serious budget. Whether it is worth it depends on the property, area, and how much value and usable space the project adds.

Frequently asked questions

How much does a single-storey extension cost in the UK?

A broad current range is £30,000 to £140,000, with many projects budgeted by m² at around £2,200–£3,300 per m² excluding VAT.

How much does a double-storey extension cost?

A broad current range is about £108,000 to £180,000, though quality and size matter a lot.

How much is a 30m² extension?

Homebuilding’s 2026 guide gives a 30m² single-storey extension at roughly £66,000–£99,000 plus VAT.

Do extension costs vary by region?

Yes. Costs are often higher in London and the South East.

Related guides

“See full Home Costs guide”

Final note

For a useful rule of thumb, £2,200 to £3,300 per m² excluding VAT is a sensible modern starting point for a standard single-storey extension in the UK, but the real total can move a long way depending on size, finishes, structure, and location.