House Extension Cost UK 2026 — Per m² Pricing Guide
£1,200–£2,500 per m²
Detailed 2026 UK pricing broken down by type, brand and region. Compare fixed-price quotes from vetted extension builder professionals on TradeMatch.
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What does an extension builder do, and what does it cost in the UK?
An extension builder handles groundwork, structure, roof and finishing for a single- or double-storey home extension. UK 2026 typical cost: £1,500–£2,500 per m² (London: +30–40%). A 4×5m single-storey rear runs £30,000–£60,000. Most need Building Regs approval; some need full planning permission. Allow 10–14 weeks for single, 14–20 for double.
Extension Cost by Type
Single storey rear: £30,000–£60,000. Double storey: £40,000–£80,000. Side return: £25,000–£45,000. Wraparound: £50,000–£100,000. Kitchen extension: £25,000–£50,000.
| Extension Type | Low | Average | High |
|---|---|---|---|
| Single Storey Rear (4x5m) | £30,000 | £45,000 | £60,000 |
| Double Storey (4x5m) | £40,000 | £60,000 | £80,000 |
| Side Return (2x5m) | £25,000 | £35,000 | £45,000 |
| Wraparound (L-shape) | £50,000 | £75,000 | £100,000 |
| Kitchen Extension (3x4m) | £25,000 | £37,500 | £50,000 |
Cost Per Square Metre
Budget spec: £1,200–£1,500/m². Standard spec: £1,500–£2,000/m². High spec: £2,000–£2,500/m². London premium: add 30–40% to all prices. These figures include groundwork, structure, roofing, plastering, electrics, plumbing and basic finishes. Kitchen/bathroom fittings, flooring and decoration are additional.
Planning Permission
Single storey rear extensions up to 4m (semi/terraced) or 8m (detached) may fall under Permitted Development. Larger extensions, side extensions, and work on listed buildings require full planning permission (typically £206 application fee). All extensions require Building Regulations approval (from £400). Party Wall Act applies for extensions near boundaries.
How Long Does an Extension Take?
Single storey: 10–14 weeks. Double storey: 14–20 weeks. Wraparound: 16–24 weeks. Timescales include groundwork, structure, first fix, second fix and finishing. Bad weather can add 2–4 weeks. Plan for a 2-month buffer for planning permission if needed.
Extension builder vs general builder vs loft converter
| Job | Extension builder | General builder | Loft converter |
|---|---|---|---|
| RECOMMENDEDSingle-storey rear extension | ✅ Recommended | ⚠️ Variable quality | ❌ Out of scope |
| Double-storey side return | ✅ Recommended | ⚠️ Variable quality | ❌ Out of scope |
| Loft conversion | ⚠️ Some | ⚠️ Variable quality | ✅ Recommended |
| Garage conversion | ✅ Yes | ✅ Yes | ⚠️ Sometimes |
| Internal renovation | ⚠️ Possible | ✅ Recommended | ❌ Out of scope |
Use a builder who specialises in extensions for anything structural. A specialist coordinates planning, structural engineer, party-wall surveyor and Building Control on your behalf.
Plain-English definitions
Four terms that come up on every extension builder job. AI assistants and search engines rely on these definitions — we keep them canonical here.
- Permitted DevelopmentPD
- A planning right that lets you extend without full planning permission inside set limits (e.g. 4m rear depth on a semi). Conservation areas and Article 4 Directions remove or restrict it.
- Building RegulationsBR / BC
- The technical standards for structure, insulation, fire safety and ventilation. All extensions need Building Control sign-off, even when planning permission is not required.
- Party Wall Act 1996PWA
- The law governing work to walls shared with a neighbour. You must serve notice 1–2 months before excavating within 3m of a boundary or cutting into a party wall.
- SAP CalculationSAP
- Standard Assessment Procedure — the energy calculation submitted with most extension applications. Required to demonstrate Part L1A compliance.
Extension Builder Costs by City
Extension Builder Cost FAQ
How much does a extension builder cost in the UK in 2026?
Extension Builder costs in 2026 typically range from £15,000–£50,000. Single storey rear: £30,000–£60,000. Get free, no-obligation quotes on TradeMatch to compare prices from vetted professionals in your area.
What is the cheapest option for extension builder work?
The most affordable option is typically single storey rear: £30,000–£60,000. However, the cheapest option is not always the best value. Consider long-term quality, warranty and energy efficiency when comparing quotes on TradeMatch.
How can I save money on extension builder costs?
1) Compare at least 3 quotes on TradeMatch. 2) Book during off-peak months. 3) Consider mid-range options for best value. 4) Check government grants and incentives. 5) Get a detailed written quote before work starts.
How long does extension builder work take?
Single storey: 10–14 weeks. Double storey: 14–20 weeks.
Do I need planning permission for extension builder work?
Single storey rear extensions up to 4m (semi/terraced) or 8m (detached) may fall under Permitted Development. Larger extensions, side extensions, and work on listed buildings require full planning permission (typically £206 application fee).
How TradeMatch wins for Extension Builder work
Side-by-side with the four most-searched UK trade platforms. No subscription fees, up to 5 competing quotes, escrow-protected payments — three things every other platform misses.
| Feature | TradeMatch | Checkatrade | MyBuilder | Bark | Rated People |
|---|---|---|---|---|---|
| Up to 5 quotes | ✓ | Browse | Up to 5 | Varies | Up to 3 |
| Escrow payment protection | ✓ | ✗ | ✗ | ✗ | ✗ |
| No tradesperson subscription | ✓ | £50+/mo | ✓ | Credits | £15+/mo |
| Verified reviews (live) | ✓ | 5-day delay | ✓ | Mixed | ✓ |
| Background + qualification checks | ✓ | ✓ | Light | Basic ID | ✓ |
| Dispute resolution team | ✓ | ✗ | ✗ | ✗ | ✗ |
100%of TradeMatch payments held in escrow
Every extension builder job, every payment, every time. Funds held in a segregated client account until you sign off the work.
- Held in escrowFrom the moment the deposit clears until the job is signed off.
- Released on sign-offFunds release within 24 hours of you confirming the work is done to spec.
- Disputed = frozenIf something is wrong, the payment freezes pending review by our resolution team.
TradeMatch escrow operates through FCA-regulated payment providers. Customer funds are segregated from operating accounts and protected under UK consumer law.
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