Single Storey Extension Cost Calculator UK
Get a 2026 single storey extension cost estimate in 30 seconds. Spec level, floor area, kitchen or bathroom fit-out, glazing and region — real UK supply-and-fit rates including VAT. No email required.
Estimate Your Single Storey Extension Cost in 30 Seconds
5 steps. Covers foundations, shell, roof, glazing, plastering, decoration and VAT. Professional fees (10–15%) and contingency are flagged separately in the result notes.
How This Calculator Works
Our single storey extension calculator combines spec level, floor area, fit-out and region with real 2026 UK build pricing from vetted builders across our 519-town database.
Build Rates (per m², complete)
- Basic spec — £1,700–£2,000/m²
- Standard spec — £1,900–£2,600/m²
- Premium / glass-heavy — £2,800–£3,500/m²
- Kitchen fit-out +£15,000 · bathroom/utility +£6,000
- Bifold/sliding doors +£5,000 · structural glazing feature +£12,000
Rates include foundations, shell, roof, glazing, plastering, decoration, labour and VAT.
Assumptions & Adjustments
- Add 10–15% for professional fees (architect, engineer, surveys) and 10–15% contingency
- Permitted development: rear extensions up to 3m (semi/terraced) or 4m (detached) usually need no planning
- Party wall agreements £700–£1,500 per affected neighbour where applicable
- Region multipliers: London +27% … Northern Ireland −12% (Midlands baseline)
- Estimate only — a firm quote always follows a site survey
Building regulations always apply to habitable extensions — your builder handles sign-off.
Typical Single Storey Extension Costs (2026)
Complete build incl. foundations, shell, roof, glazing, decoration & VAT, Midlands baseline. Professional fees (10–15%) and contingency extra.
| Scenario | Size | Cost range |
|---|---|---|
| Standard spec | 15 m² (3×5m) | £28,500–£39,000 |
| Basic spec | 20 m² | £34,000–£40,000 |
| Standard spec | 20 m² (4×5m) | £38,000–£52,000 |
| Standard spec + kitchen fit-out | 25 m² | £62,500–£80,000 |
| Premium / glass-heavy | 30 m² | £84,000–£105,000 |
Want the full method and per-material detail? Read the complete 2026 roofing cost guide.
Frequently Asked Questions
How much does a single storey extension cost in 2026?
Do I need planning permission for a single storey extension?
How much does a kitchen extension add on top of the build?
What is not included in the calculator estimate?
How long does a single storey extension take to build?
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