Estimate 2026 UK loft conversion costs across Rooflight/Velux, Rear Dormer, Hip-to-Gable, and Mansard builds by floor area (m²), en-suite bathroom options, Party Wall fees, and UK region.
In the UK in 2026, a loft conversion costs £28,000 to £42,000 for a Velux/rooflight conversion, £45,000 to £68,000 for a rear dormer conversion, £55,000 to £78,000 for a hip-to-gable conversion, and £68,000 to £98,000+ for a full mansard conversion. Per square metre, UK loft conversions average £1,250 to £2,250/m².
📐 Engineering Formula Used: Total Cost (£) = (Loft m² × Structural Rate × UK Region) + En-Suite Bathroom + Plans/Building Regs + Party Wall
The table below provides verified 2026 material, labor, and installed turnkey cost ranges for loft conversion cost calculator UK projects. Compare these figures alongside live industry benchmarks such as LoftConversionCostCalculator.co.uk & PlanningScout.co.uk ↗.
| Loft Conversion Type | 2026 Cost Per m² (UK) | Typical 35 m² Loft Total | Planning Permission Needed? | Build Time |
|---|---|---|---|---|
| Velux / Rooflight Loft | £950 – £1,250/m² | £32,000 – £43,000 | No (Permitted Development) | 4 – 6 Weeks |
| Rear Dormer Loft Conversion | £1,350 – £1,750/m² | £47,000 – £64,000 | Usually Permitted Development | 6 – 9 Weeks |
| Hip-to-Gable Loft Conversion | £1,600 – £2,000/m² | £56,000 – £74,000 | Permitted Dev (Under 50m³) | 7 – 10 Weeks |
| L-Shaped Victorian Dormer | £1,650 – £2,100/m² | £58,000 – £78,000 | Permitted Dev (Terraced <40m³) | 8 – 11 Weeks |
| Mansard Loft Conversion | £1,950 – £2,500/m² | £68,000 – £95,000+ | Yes (Full Planning Required) | 10 – 14 Weeks |
Project Scenario: 35 m² Rear Dormer Loft Conversion (Master Bedroom + En-Suite) on Semi-Detached UK Home
| Itemized Quote Line Item | 2026 Estimated Cost |
|---|---|
| 35 m² Rear Dormer Shell, RSJ Steel Beams, Floor Joists, Insulation & Stairs (@ £1,520/m²) | £53,200 |
| En-Suite Shower Room — Tiling, Sanitaryware & Soil Pipe Connection | £6,800 |
| Architectural Drawings, Structural Engineer RSJ Calculations & Building Control | £2,950 |
| Party Wall Notice & Surveyor Award with Adjoining Neighbour | £1,400 |
| Estimated Total Turnkey UK Loft Conversion Cost | £64,350 (£1,838.57/m²) |
To qualify for a loft conversion without lowering the first-floor ceilings, your existing roof ridge height needs at least 2.2 metres (7 ft 2 in) of vertical clearance from the top of the ceiling joists to the underside of the ridge timber. UK Building Regulations also mandate a minimum 2.0m headroom above the new staircase pitch line and FD30 fire doors along the escape hallway.
Most rear dormer and hip-to-gable loft conversions fall under UK Permitted Development rights (no full planning application required) provided the added roof volume does not exceed 40 cubic metres for terraced houses or 50 cubic metres for semi-detached and detached houses.
Calculate 2026 installed retaining wall costs by wall-face square footage (length × height), material type (pressure-treated timber, interlocking Allan block, poured concrete, or natural stone), drainage backfill, and slope grading.
Estimate 2026 French drain installation costs per linear foot for exterior yard drainage, curtain drains, or interior basement perimeter systems, including gravel tonnage and sump pump options.
Calculate 2026 concrete driveway installation costs by length, width, slab thickness (4" vs. 6"), PSI mix, rebar grid vs. wire mesh reinforcement, decorative stamped finishes, and old pavement tear-out.
Calculate 2026 UK resin-bound driveway installation costs per square metre (m²) comparing overlays on existing tarmac/concrete vs. full sub-base dig-outs, UV-stable polyurethane resin, and block edging.
Calculate 2026 UK single-storey rear, side-return, or wrap-around house extension costs per square metre (m²) by width, depth, spec level, bi-fold doors, kitchen fit-out, and UK region.
Calculate 2026 UK double-storey (two-floor) house extension costs per square metre (m²), taking advantage of shared foundation and roof economies of scale across ground and first floors.