How Much Does a House Extension Cost in 2026? UK Price Guide
Realistic UK house extension costs for 2026. Single-storey, two-storey, side return and wrap-around — with material breakdowns, regional pricing, and what affects the final bill.
What Does a House Extension Actually Cost in the UK?
If you’ve Googled “house extension cost UK” you’ve probably seen wildly different numbers. That’s because extension costs depend on size, spec, location, ground conditions and a dozen other factors. This guide gives you realistic, itemised costs based on what UK builders are actually charging in 2026.
Extension Cost Summary Table
| Extension Type | Size | Typical Cost Range (2026) | Cost per m² |
|---|---|---|---|
| Single-storey rear | 3m × 4m (12 m²) | £25,000 – £35,000 | £1,800 – £2,500 |
| Single-storey rear | 4m × 5m (20 m²) | £38,000 – £55,000 | £1,800 – £2,500 |
| Side return (Victorian terrace) | 2m × 6m (12 m²) | £22,000 – £32,000 | £1,700 – £2,400 |
| Wrap-around | 20–30 m² | £45,000 – £75,000 | £2,000 – £2,800 |
| Two-storey rear | 3m × 4m per floor | £45,000 – £70,000 | £2,000 – £2,800 |
| Two-storey rear | 4m × 5m per floor | £65,000 – £100,000 | £2,000 – £2,800 |
| Over-garage extension | 3m × 6m (18 m²) | £30,000 – £50,000 | £1,800 – £2,500 |
Prices are for England outside London. London and South East: add 25–40%. Scotland and Wales: similar or slightly lower.
What’s Included in These Prices?
The cost ranges above assume a mid-spec finish and include:
- Architectural drawings and Building Regulations
- Groundworks and foundations
- External walls (cavity masonry)
- Roof structure and covering
- Windows and external doors (standard double-glazed)
- First fix plumbing, electrics, and carpentry
- Plastering and internal finishes
- Second fix and decoration
- Basic kitchen or bathroom (if applicable)
Not typically included: planning application fees (£258 for householder), party wall agreements (£800–1,500 per neighbour), furniture, appliances, landscaping.
Cost Breakdown: Typical 4m × 5m Single-Storey Extension
Here’s what the build cost actually looks like when broken down by trade:
| Work Stage | Cost Range | % of Total |
|---|---|---|
| Foundations & groundworks | £5,000 – £8,000 | 13–15% |
| Masonry (walls) | £5,500 – £8,000 | 14–16% |
| Roof structure & covering | £3,500 – £6,000 | 9–11% |
| Windows & external doors | £3,000 – £6,000 | 8–11% |
| First fix (plumbing, electrics, carpentry) | £4,000 – £6,000 | 10–12% |
| Plastering | £2,500 – £4,000 | 6–8% |
| Second fix & finishes | £3,000 – £5,000 | 8–10% |
| Kitchen installation | £5,000 – £12,000 | 13–22% |
| Decoration | £1,500 – £2,500 | 4–5% |
| External works (drainage, patio make-good) | £2,000 – £4,000 | 5–8% |
| Total | £35,000 – £61,500 |
What Makes Extensions Expensive?
Foundations
If your soil has poor bearing capacity, trees nearby (clay heave risk), or you’re building near a drain, you may need piled foundations instead of standard strips. This can add £5,000–15,000.
Roof Type
A flat roof (GRP or EPDM) is the cheapest option for single-storey. A pitched roof with tiles adds £3,000–6,000. A zinc standing seam or green roof adds more still.
Glazing
Standard casement windows are budget-friendly. Bifold doors (3–4 panels) cost £3,000–6,000 installed. Structural glazing or roof lanterns add £2,000–5,000.
Kitchen Spec
A basic kitchen (flat-pack units, laminate worktops) costs £3,000–5,000. A mid-range kitchen (soft-close, quartz worktops) costs £8,000–15,000. A high-end kitchen can easily exceed £25,000.
Regional Price Variations
| Region | Cost Multiplier |
|---|---|
| London | 1.30 – 1.45× |
| South East | 1.15 – 1.30× |
| South West | 1.00 – 1.10× |
| Midlands | 0.95 – 1.05× |
| North West | 0.90 – 1.00× |
| North East | 0.85 – 0.95× |
| Scotland | 0.90 – 1.05× |
| Wales | 0.85 – 0.95× |
Planning Permission & Building Regulations
Permitted Development allows certain extensions without planning permission:
- Attached houses: up to 3m rear (or 6m with prior approval)
- Detached houses: up to 4m rear (or 8m with prior approval)
- Maximum height: 4m for single-storey, 3m at the eaves
- Two-storey: almost always requires full planning
Building Regulations approval is always required, regardless of planning. Expect £500–1,500 for the application and inspections.
How to Get an Accurate Extension Quote
The numbers above are guide ranges. For an accurate, project-specific quote you need:
- Architectural drawings — even outline sketches help a builder price accurately
- Detailed specification — material choices, window types, kitchen/bathroom spec
- Site survey — ground conditions, access, drainage locations
EasyEstimate helps builders produce detailed, itemised extension quotes with live UK material prices, labour rates, and 140+ built-in calculators. Every cost is broken down by trade and material — so you know exactly where the money goes.
Get a professional extension estimate → | Price it yourself with our software →
Related Resources
- Builders Quote Template — how to structure a professional building quote
- Construction Estimating Software — price extensions with live UK costs
- Brick Calculator — calculate bricks for extension walls
- Concrete Calculator — calculate concrete for foundations
- Roofing Calculator — calculate tiles for extension roofs
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