UK Home Extension Costs: Complete Guide
Guide updated 2 October 2026 (scope and methodology clarified; pricing assumptions not re-reviewed).
How much does a house extension cost in the UK?
UK extension costs typically range from £1,500 to £3,500 per square metre for a standard build. Single-storey extensions commonly fall between £30,000 and £60,000, larger single-storey or kitchen extensions between £40,000 and £100,000, and two-storey extensions between £90,000 and £220,000 or more.
What this covers: Structural shell, roof, windows and doors, and internal finishing for a typical domestic extension.
What changes the cost: Floor area, ground conditions and foundations, glazing specification, kitchen or bathroom fit-out, site access and the regional labour market.
These are indicative planning ranges for 2026 UK pricing, not contractor quotations or confirmed final costs. Property size, condition, location and specification all affect the final figure. Use the RenoCost renovation calculator for a range based on your own property, or obtain detailed written quotations before committing.
Get your personalised extension cost estimate in under 30 seconds
Start Your EstimateBuilding an extension is one of the most popular ways to add space and value to your UK home. Costs vary considerably based on the type of extension, your location and the specification of finishes. This guide provides realistic cost ranges to help you plan your budget. For broader renovation projects beyond extensions, see our full house renovation cost guide.
How This Estimate Is Built
Estimates are calculated from published UK cost benchmarks and RenoCost's own per-module cost assumptions, adjusted by postcode-based pricing region. Outputs are shown as low, mid and high ranges for initial planning, not contractor quotations. Every input is a deliberate user choice; no defaults are applied. Always obtain written quotations before committing to a project.
Average UK Extension Costs
Extension costs in the UK typically range from £1,500 to £3,500 per square metre for a standard build. Total price ranges below are based on typical project sizes; larger or more complex extensions can cost significantly more.
Side Return
£30,000-£60,000
typical size 10 to 20m²
Single-Storey Rear
£40,000-£100,000
typical size 20 to 35m²
Two Storey
£90,000-£220,000+
typical combined size 40 to 80m²
Worked example
A 130m² two-storey extension at £2,150 per m² would cost about £279,500. This illustrates how larger extensions quickly exceed the headline card ranges above.
Figures may exclude VAT, professional fees, kitchens, bathrooms, flooring, decorating and unforeseen work unless stated. Always treat estimates as planning guides, not fixed quotes.
What to check in an extension budget
These are scope checks, not additional quoted prices. A contractor’s written specification decides what is included in any actual offer.
| Item | RenoCost extension estimate | Check separately |
|---|---|---|
| Build work | Extension module labour and materials, adjusted for your selections | Exact foundations, glazing, services, finishes and site conditions in the quote |
| Other rooms | Kitchen and bathroom work only when selected as separate modules | Fittings and any work not selected |
| Fees and VAT | Not separately itemised; VAT basis not explicit | Professional and approval fees; supplier’s VAT treatment |
| Contingency | Shown separately from the estimated cost range | Unforeseen work and your total available budget |
For homeowners with an underused garage, converting existing space may cost less than constructing a new extension, although it can mean losing parking or storage. See our garage conversion cost guide for typical UK planning ranges.
What Affects Extension Costs?
Extension costs are influenced by many of the same factors as general renovations. Regional labour rates play a major role — our renovation costs by postcode guide shows how prices differ across the UK. You can also use per-square-metre benchmarks to estimate build costs for your extension size.
- • Size and type of extension
- • Foundation requirements and ground conditions
- • Roof type and materials
- • Regional labour rates
- • Planning permission and building regulations
- • Internal finishes and fixtures
Extension Cost Guides
From the Insights
Data-led analysis on UK renovation and extension pricing — useful context when planning your project budget.
Year-on-year movement in UK renovation and extension pricing, broken down by project type.
Average Renovation Costs by RegionRegional cost benchmarks across the UK — the same regional spread applies to extension build costs.
Hidden Costs Homeowners MissStructural surprises, fees, finance and finishing creep — the items that push extension budgets over.
Live UK Renovation Data
Live, anonymised extension activity from completed RenoCost calculator sessions — updated automatically.
Sources & Methodology
Pricing on this page is informed by a mix of public macro benchmarks and RenoCost's own datasets and assumptions, listed below. See the Method Glossary for definitions of the terms used.
- RenoCost method glossaryExplains the difference between external benchmarks, RenoCost assumptions, planning ranges and quotations.
- RenoCost: how the calculator worksExplains the selected modules, postcode adjustments and limits of a planning estimate.
- Planning PortalOfficial guidance on planning and building regulations in England; check local requirements for your property and nation.
- HMRC: VAT for buildersOfficial guidance on VAT for work on houses and flats; the applicable treatment must be confirmed for each quote.
- ONS construction statisticsPublic macro context for UK construction trends, not a direct input or validation of the extension module.
External benchmarks above are used only as macro reference points. None of the organisations listed has reviewed, endorsed, validated or partnered with RenoCost. Specific cost figures on RenoCost reflect RenoCost's own per-module assumptions and completed calculator estimates, and should not be attributed to any external body.
How We Calculate Costs
RenoCost estimates are calculated from published UK cost benchmarks and RenoCost's documented per-module cost assumptions. The model adjusts these assumptions using the property characteristics, selected renovation scope, finish level and broad postcode-based pricing region, then presents a low, mid and high planning range.
- Published UK benchmarks — macro reference points for construction costs and materials and labour trends, used to sense-check RenoCost's own assumptions.
- RenoCost's per-module assumptions — cost and duration assumptions for each renovation module, reviewed and updated periodically by RenoCost.
- Estimate ranges — low, mid and high bands set to reflect the realistic spread between competitive and premium specifications, rather than a single fixed price.
Data confidence note
Completed calculator estimates are used to produce anonymous renovation-planning insights. They are not contractor quotations, invoices or confirmed final project costs. RenoCost estimates are intended for initial planning and budgeting. Property condition, specification, access, contractor availability and site-specific requirements can change the final cost. Always obtain detailed written quotations before committing to a project.
Regional adjustments are applied based on postcode area to reflect broad differences in local labour and material rates. See our Method Glossary for definitions of the terms used here.