House Extension Cost UK
Estimates based on UK trade benchmark data, updated 25 April 2026. Methodology →
A house extension — also referred to as a home extension or building an addition — is one of the most significant home improvements you can undertake. Whether you're adding a rear extension, a single-storey or double-storey extension, or a wraparound, costs depend on size, specification, structural requirements, and where you live. This guide covers typical UK prices for rear, single-storey, and double-storey extensions to help you plan your budget.
Most projects fall between £54,000 and £90,000. Budget refreshes start near £30,000; premium projects reach up to £264,000.
Typical UK Cost by Scenario
Typical timeline: 8 to 16 weeksBudget
£39,000
typical figure
- Basic single-storey footprint increase with standard glazing
- Straightforward finishes
Mid-range
Most common£72,000
typical figure
- Kitchen-diner extension with rooflights
- Good insulation
- Moderate internal reconfiguration
Premium
£204,000
typical figure
- Complex steelwork
- Premium glazing
- Bespoke joinery
Figures are typical UK averages including labour, materials, and VAT at 20% for standard-rated work.
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Typical UK Cost Ranges for Extension
| Item | Cost Range |
|---|---|
| Single-storey rear (small, 15 m²) | £24,000 – £48,000 |
| Single-storey rear (medium, 25 m²) | £42,000 – £78,000 |
| Single-storey build (per m²) | £1,440 – £3,360 |
| Double-storey (25 m² total) | £54,000 – £84,000 |
| Double-storey (40 m² total) | £72,000 – £114,000 |
| Double-storey build (per m²) | £1,200 – £2,640 |
| Side return extension | £18,000 – £48,000 |
| Wraparound extension | £48,000 – £144,000 |
| Foundations | £3,600 – £12,000 |
| Design and planning | £2,400 – £7,200 |
All prices are approximate UK averages including labour, materials, and VAT at 20% (2026). Some qualifying renovations for empty homes may use the reduced 5% VAT rate.
Real UK Cost Examples
- Budget scenario (small rear extension, 2-bed terrace, North West): Basic single-storey footprint increase with standard glazing and straightforward finishes. Not done: full internal reconfiguration or premium kitchen fit-out. Approx cost: £25,000 to £40,000.
- Mid-range scenario (3-bed semi rear extension, Bristol): Kitchen-diner extension with rooflights, good insulation and moderate internal reconfiguration. Approx cost: £45,000 to £75,000.
- High-end scenario (wraparound extension, London commuter belt): Complex steelwork, premium glazing, bespoke joinery and major drainage or service relocation. Main cost drivers: structure, glazing package and fit-out. Approx cost: £120,000 to £220,000.
Related next steps:
What You Can Get For Your Budget
- Around £40,000: modest single-storey rear extension with practical specification and limited internal knock-through.
- Around £75,000: larger usable family space with better glazing, rooflights and more integrated internal changes.
- £140,000+: complex geometry, premium envelope, heavy steelwork and full internal layout integration.
Hidden Costs to Watch For
- Foundation depth can increase after ground investigation or Building Control direction.
- Drain diversions and manhole relocations regularly add late-stage civil costs.
- Temporary kitchen or accommodation costs are often omitted from initial budgets.
- Party wall surveyor fees and planning-condition discharges can materially increase soft costs.
Related next steps:
Should You Do This Renovation?
- Usually worth it when space constraints are the main pain point and moving costs are high.
- Less worth it when budget is stretched and similar utility could be achieved by reconfiguring existing rooms.
- Extensions can drive strong long-term value in demand-heavy areas, but payback varies widely by postcode and over-spec risk.
Common Cost Mistakes
- Underestimating preliminaries and site setup in headline per-m² assumptions.
- Changing glazing and rooflight strategy after structural design is fixed.
- Selecting builders on lowest price rather than programme realism and inclusion detail.
- Ignoring a 15% contingency on structural-heavy projects.
Key Cost Factors
- Size and type of extension — single-storey, double-storey, or wraparound.
- Foundations — ground conditions, proximity to trees, and drainage.
- Specification level — basic build vs. high-end finishes.
- Structural requirements — steel beams, underpinning, party wall work.
- Planning permission and building regs — fees and compliance costs.
- Utilities — relocating gas, water, drains, or electrics.
- Finishing and fit-out — kitchen, bathroom, or living space finishes.
Cost per m² by Extension Type
- Rear extension costs are often the baseline due to simpler massing and straightforward planning routes.
- Side returns can be efficient on Victorian terraces but may involve steelwork and drainage diversions.
- Wraparound extensions usually carry the highest totals due to structure, glazing, and full internal reconfiguration.
Typical Timeline
| Item | Duration |
|---|---|
| Design and planning | 4 to 16 weeks |
| Single-storey rear extension | 8 to 12 weeks |
| Double-storey extension | 12 to 16 weeks |
| Wraparound extension | 14 to 20 weeks |
Regional Cost Variations
Extension costs in London are typically 30–50% higher than the national average due to higher labour, material transport, and planning costs. The South East is also above average, while the North and Midlands offer the best value.
Costs in your area
Compare regional benchmarks for house extension using the same UK baseline assumptions.
Ways to Reduce Costs
- Use permitted development rights to avoid planning permission fees where possible.
- Choose a simple rectangular footprint — complex shapes cost more.
- Manage the project yourself if you have experience to save on project management fees.
- Use standard window sizes and materials to reduce lead times and costs.
- Get structural engineer quotes directly rather than through the architect.
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