Brick vs Timber Frame Extension 2026 UK: Full Comparison
Cost: brick at £2,400–£3,200/m² vs timber frame at £2,100–£2,800/m² — timber frame 8–15% cheaper on like-for-like spec. Build speed: timber frame is on the warm-and-watertight stage 30–40% faster on-site. Energy: timber frame hits 0.18 W/m²K U-value with thinner walls. Lifespan: brick wins on 100–150 yr horizons; modern timber frame is 80–120 yr if detailed correctly. Mortgageable: both, on every UK high-street lender as of 2025.
Planning the work? Check what it usually costs, or work out your own estimate. The free quote form is at the top of this page.
Brick vs timber frame extension — which should I choose in 2026?
Headline 2026 UK comparison — like-for-like 30 m² single-storey rear extension:
- Cost: brick £72,000–£96,000 vs timber frame £63,000–£84,000 (timber 8–15% cheaper)
- On-site time: brick 14–18 weeks vs timber frame 9–12 weeks (warm-and-watertight in 5–6 weeks vs 9–10)
- U-value (walls): brick 0.21–0.24 W/m²K typical, timber frame 0.16–0.20 W/m²K typical
- Wall thickness: brick 295 mm cavity wall, timber frame 240–265 mm engineered (extra interior floor area)
- Lifespan: brick 100–150 yr, modern timber frame 80–120 yr
- Mortgage: both fully mortgageable on every UK high-street lender as of 2025
Best for brick: period properties, Conservation Areas, traditional UK estates where matching the existing fabric matters. Best for timber frame: contemporary builds, tight build-window projects, energy-led upgrades, anywhere internal floor area matters per pound spent.
Full 2026 UK side-by-side comparison
Headline numbers across cost, build speed, energy, lifespan and resale on a typical 30 m² single-storey rear extension.
What each method is and isn't good at
Traditional brick (cavity wall) — the UK default
Pros: 100–150 yr lifespan, near-perfect aesthetic match to existing UK housing stock, excellent acoustics, near-zero risk of moisture-related defects, every UK builder can detail it, every lender accepts it. Cons: 30–40% slower on-site than timber frame, harder to hit modern U-values without thicker walls (cavity insulation upgrade needed), more weather-dependent (brickies down tools below 2°C), heavier loadings on existing foundations. Best for: period properties, Conservation Areas, all UK suburban housing stock pre-2000, projects where matching existing brickwork matters more than build speed.
Timber frame — the modern energy-led method
Pros: 30–40% faster on-site (factory-precut panels), thinner walls (240–265 mm) deliver more internal floor area, easier to hit Building Regs Part L U-values, lower embodied carbon (FSC-certified softwood), can be erected in poor weather (waterproof PE membrane day 1). Cons: requires careful detailing of vapour control layer (failures lead to interstitial condensation), 80–120 yr lifespan rather than 100–150, twin-leaf detail needed for party wall acoustics, less aesthetic flexibility on heritage-match elevations. Best for: contemporary builds, energy-retrofit-led extensions, tight build-window projects, designs where every cm of internal floor area counts.
SIPS & ICF — honourable mentions
SIPS (Structural Insulated Panels) deliver U-values down to 0.13 W/m²K and are the fastest construction method available (warm-and-watertight in 4–5 weeks). 8–15% pricier than standard timber frame. ICF (Insulating Concrete Formwork) gives brick-like mass and acoustic performance with timber-frame-like U-values. 10–18% pricier than brick. Both are mortgageable but lender choice is narrower than brick or standard timber frame.
Real 2026 Bristol 32 m² rear extension — brick vs timber frame quotes
A real homeowner project we reviewed in February 2026: 1930s 3-bed semi in Bristol BS9, single-storey rear kitchen extension, 32 m² internal area, three-leaf bi-fold door run, slate roof to match existing.
The owner chose timber frame with brick slips on the visible elevation: £78,400 total, 11 weeks on-site, 30.7 m² net internal floor area (1.1 m² more than brick — enough for a usable larder cupboard), U-value 0.18 vs 0.22 for brick. The matching brick-slip outer leaf was visually indistinguishable at street level. Net result: £6,800 cheaper than brick, finished 6 weeks earlier, with 1.1 m² more usable space and a marginally lower running cost.
Common Questions
How we sourced these figures
- RICS BCIS — UK construction cost benchmarks for both methods
- FMB cost guides — Federation of Master Builders extension cost dataset
- Building Regulations 2010 (Part L 2025 update) — U-value targets for new extensions
- Structural Timber Association — Timber frame lifespan and detailing data
- Brick Development Association — Cavity-wall lifespan studies and U-value performance
Methodology note: Cost ranges combine RICS BCIS rates and our internal dataset of 2,200+ UK extension quotes reviewed in the 12 months to 30 April 2026.
Related Guides
More UK extension guides.