House Extension Cost Index UK 2026
How much does house extension cost in 2026 — and how much more do you pay in London versus the cheapest UK regions? This BestBuilders study compares real 2026 quote data for a standard single-storey extension across all 14 UK regions. The headline: it costs up to 52% more in London (£11,500 more in absolute terms) than in Merseyside & North Wales · South Wales.
The regional gap: London pays up to 52% more for house extension
A standard single-storey extension starts at £33,500 in London versus £22,000 in Merseyside & North Wales · South Wales — a £11,500 gap. That's a +52% London premium on the same job spec, driven mainly by labour rates and, on smaller jobs, access and permit costs. The pattern is consistent with RICS BCIS and FMB benchmark data.
House Extension cost by UK region, 2026
Typical "starting from" prices for a standard single-storey extension, ranked most to least expensive region. Range shows the typical low-to-high spread within each region.
| UK region | Starting from | Typical range | Vs cheapest |
|---|---|---|---|
| London | £33,500 | £33,000 – £67,000 | +£11,500 (+52%) |
| South East | £30,000 | £30,000 – £60,000 | +£8,000 (+36%) |
| Southern (Hampshire, Wiltshire, Dorset) | £27,500 | £27,000 – £55,000 | +£5,500 (+25%) |
| Eastern (East Anglia) | £27,000 | £27,000 – £54,000 | +£5,000 (+23%) |
| East Midlands | £25,000 | £25,000 – £50,000 | +£3,000 (+14%) |
| West Midlands | £25,000 | £25,000 – £50,000 | +£3,000 (+14%) |
| North West | £23,500 | £23,000 – £50,000 | +£1,500 (+7%) |
| Yorkshire & Humber | £23,500 | £23,000 – £47,000 | +£1,500 (+7%) |
| South West | £23,000 | £23,000 – £46,000 | +£1,000 (+5%) |
| Scotland (Central & South) | £23,000 | £23,000 – £46,000 | +£1,000 (+5%) |
| Scotland (Highlands & North) | £23,000 | £23,000 – £46,000 | +£1,000 (+5%) |
| North East | £22,500 | £22,000 – £45,000 | +£500 (+2%) |
| Merseyside & North Wales | £22,000 | £22,000 – £44,000 | baseline |
| South Wales | £22,000 | £22,000 – £44,000 | baseline |
Want your local figure? Try our full house extension cost guide or get three free quotes below.
What sets the price for house extension?
The three main options homeowners typically choose from — and how they change the total:
- Single-Storey Extension. The most popular choice for UK terraces and semis. Adds a kitchen-diner or extra living space at ground level. Typically 3–5m deep, completed in 10–14 weeks.
- Double-Storey Extension. Maximum space gain in a single build — adds a ground-floor room and a bedroom above. Strong ROI in most UK property markets. Requires full planning permission.
- Side Extension. Ideal for terraced homes with a narrow side alley. Transforms a cramped kitchen into a full-width open-plan space. Often combined with a rear extension.
Extension costs vary significantly by region. London and South East prices are typically 25–40% above the national average.
Why does house extension cost more in London?
The +52% London premium on a standard single-storey extension tracks the same four factors seen across BestBuilders' full 2026 dataset, matching the pattern in RICS BCIS and FMB benchmark data:
- Labour rates. Skilled-trade day rates in London and the South East run 25–40% above the national average, the single biggest factor on a labour-heavy job.
- Demand and backlogs. High demand and long waiting lists let installers in the South East price higher; quieter regional markets are more competitive.
- Access and logistics. Restricted parking, skip and scaffold permits, congestion charges and tight rear access add cost in dense urban areas.
- Property type. London's older housing stock often needs more preparation or bespoke solutions than newer regional housing, which pushes labour hours up.
The takeaway for homeowners: the regional figure is a starting point, not a quote. The spread within a region — between the cheapest and most expensive installer — is often as wide as the gap between regions, which is why comparing three quotes matters more than any headline average.
Key findings, 2026 — House Extension
- London is the most expensive UK region in 2026 for house extension, starting at £33,500 for a standard single-storey extension.
- The cheapest regions start from £22,000: Merseyside & North Wales · South Wales.
- That's a £11,500 cash gap on the same job spec — a +52% London premium.
- Values are typical "starting from" prices from BestBuilders' 2026 quote dataset across 519 UK towns in 14 regions.
- Cross-checked against RICS BCIS building-cost data and FMB member surveys — the regional pattern is consistent with both benchmarks.
Citing this study
You are welcome to cite the BestBuilders 2026 House Extension Cost Index in articles and reports. Please credit BestBuilders with a link to this page (bestbuilders.co.uk/costs/extensions-cost-index-2026).
The full regional dataset, charts and attributable commentary are available on request under a CC BY 4.0 licence — use the quote form below to get in touch and we will pass your request to our press team.
House Extension cost questions
How we built this index
Figures are BestBuilders 2026 "starting from" prices for a standard single-storey extension, averaged by region across our quote dataset covering 519 UK towns grouped into 14 regions. Prices are rounded and are intended for budgeting, not as quotes. The regional pattern — London and the South East highest, Wales, the North East and Merseyside lowest — is consistent with independent benchmarks including RICS BCIS building-cost data and FMB (Federation of Master Builders) member surveys.
Last reviewed 2026 · Next scheduled review Q4 2026 · Published by BestBuilders, a UK home-improvement quote service. Editorial standards: figures are reviewed quarterly against live quote data and cross-checked against RICS BCIS and FMB benchmarks.
Explore the detailed cost guide: house extension cost guide. Or see the UK Home Improvement Cost Index 2026 for the full nine-project cross-service comparison, and the cost guide hub for every service we track.