How Much Does a Garage Extension Cost in 2026 UK?
In 2026 UK, a single attached garage extension (15m²) costs £18,000–£26,000 fully built; a double garage (30m²) £28,000–£42,000; a garage with habitable room above reaches £42,000–£55,000. With the Future Homes Standard and updated SAP10 calculations now in force, insulation, glazing and low-carbon heating spec have all crept up — and so has the bill. Here's the 2026 cost breakdown.
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Garage extension cost at a glance — 2026 UK
- Single attached (15m², 3×5m): £18,000–£26,000 fully built
- Single detached (15m²): £15,000–£22,000 (cheaper foundations option, no fire wall to house)
- Double attached (30m², 6×5m): £28,000–£42,000
- Double detached (30m²): £24,000–£36,000
- Single + habitable room above (15m² ground, 15m² first floor): £38,000–£48,000
- Double + room above: £45,000–£55,000+
Typical build time: 6–8 weeks for single attached; 8–10 weeks for double; 10–14 weeks with first-floor room. Add 6–10 weeks for planning approval if not permitted development.
Cost by size and type, 2026 UK
Regional factor: London & South East +15–25%; North & Scotland –5–10% vs the national midpoint.
What's driving the 2026 price — Future Homes Standard impact
Three big 2026 spec changes have lifted garage-extension prices by roughly £2,500–£5,000 against a 2024 baseline:
- U-values: walls now target ≤0.18, roofs ≤0.13, floors ≤0.13. Extra 70–100mm PIR insulation, full thermal break detailing.
- Glazing: windows ≤1.4 W/m²K — typically triple-glazed or argon-filled double with low-e coating. Garage doors are not in scope but increasingly upspec'd (insulated sectional, U≤1.5).
- Heating + ventilation (if room above): radiator drop from main system or low-temperature underfloor; MVHR or dMEV often required to hit air-tightness targets ≤5 m³/h/m².
Money-saving spec tweak: spec a detached garage where access allows — drops the price 15–20% by removing the party-wall thermal-bridge detail and a fire-rated leaf wall to the house.
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Frequently asked questions
£18,000–£26,000 fully built for a 15m² attached single garage in 2026 UK. Detached drops to £15,000–£22,000 because no party-wall fire detail is needed.
Usually permitted development if single-storey, under 4m high, behind the front line of the original house and within size caps. A garage with a room above almost always needs full planning permission. Conservation areas and designated land always require approval.
6–8 weeks on site for an attached single garage, 8–10 for a double, 10–14 weeks with a habitable room above. Add 6–10 weeks lead time for planning approval and structural calcs if not permitted development.
Yes — converting an existing 15m² garage to a habitable room is £8,000–£14,000 versus £18,000+ to build new. But you lose the parking and storage. See our cost guides hub for the conversion-only breakdown.
Typically yes — a well-built garage adds £8,000–£18,000 to a mid-market UK home; a garage with a habitable room above adds £25,000–£45,000+. The uplift depends heavily on local comparables; check sold prices on similar-spec neighbours before committing.
Foundations, blockwork or timber-frame shell, roof (warm flat or pitched), garage door, one personnel door, two windows, electrics first-fix, basic floor screed, plaster, paint. Excluded: heating, kitchenette/utility fit, premium garage door upgrades, EV charger. Always ask for a line-by-line quote.
Sources used in our 2026 figures
- gov.uk — Approved Document L
- Planning Portal — Extensions & permitted development
- FMB — Federation of Master Builders
- TrustMark — Government-endorsed quality scheme
Methodology: Cost figures use BestBuilders' 2026 regional cost model (national cost guides × regional labour index) cross-referenced against published trade benchmarks.