How Much Does a Loft Conversion Cost? Real Survey Data
We analysed survey data from 1,500+ completed UK projects to get real loft conversion costs - not estimates, not guesses. London homeowners pay a 1.57x premium over the rest of the country. Here's the full breakdown by type, region, and trade.
TL;DR
A standard dormer loft conversion costs £74,000 nationally and £88,000 in London based on DesignForMe's 2025 survey of completed projects. Mansard conversions are the most expensive at £107,000-110,000 because they involve rebuilding the roof structure. Velux (rooflight-only) conversions are the cheapest route at £45,000-55,000 but add less headroom and usable floor area. London's premium is driven by labour costs - roofers charge £300-450/day in London vs £200-300 elsewhere.
£88,000
London loft conversion avg
DesignForMe 2025 survey
£56,000
Non-London loft avg
DesignForMe 2025 survey
£110,000
London mansard avg
DesignForMe 2025 survey
1.57x
London premium (standard)
London vs non-London ratio
Source: DesignForMe survey of 1,500+ completed projects (2025)
Loft Conversion Cost by Type
The type of loft conversion is the single biggest cost driver. A Velux conversion (rooflights only, no structural changes to the roof) is less than half the price of a mansard, which involves rebuilding the entire roof slope to create vertical or near-vertical walls.
| Type | UK average | London average | Non-London average | London premium |
|---|---|---|---|---|
| Velux (rooflight only) | £48,000 | £55,000 | £40,000 | 1.38x |
| Dormer (rear) | £74,000 | £88,000 | £56,000 | 1.57x |
| Hip-to-gable | £82,000 | £95,000 | £65,000 | 1.46x |
| Hip-to-gable + rear dormer | £90,000 | £105,000 | £72,000 | 1.46x |
| Mansard | £107,000 | £110,000 | £97,000 | 1.13x |
| L-shaped dormer | £95,000 | £112,000 | £74,000 | 1.51x |
Source: DesignForMe 2025 survey, Mayfair Studio analysis • Data as of 2025 survey data, 2026 pricing applied
Mansard conversions show a smaller London premium (1.13x) because specialist structural work is a higher proportion of total cost, and structural engineers charge similar rates nationally.
Regional Cost Variation
London is the most expensive region for loft conversions, but the premium varies by conversion type. Our regional multiplier model, built from ConcreteMath trade rates and Costmodelling indices, shows inner London at 1.25x and outer London at 1.22x against a Midlands baseline.
| Region | Multiplier | Estimated cost | Key driver |
|---|---|---|---|
| Inner London | 1.25x | £88,000-95,000 | Labour rates + access constraints |
| Outer London | 1.22x | £82,000-90,000 | Labour rates |
| South East | 1.12x | £72,000-80,000 | Proximity to London labour market |
| South West | 1.05x | £65,000-72,000 | Lower labour, higher transport |
| East of England | 1.04x | £64,000-70,000 | Mixed urban/rural |
| East Midlands | 1.00x | £60,000-68,000 | Baseline region |
| West Midlands | 1.02x | £62,000-69,000 | Urban centres slightly above baseline |
| Yorkshire & Humber | 0.97x | £57,000-64,000 | Lower labour costs |
| North West | 0.98x | £58,000-65,000 | Manchester premium, wider region lower |
| North East | 0.93x | £53,000-60,000 | Lowest labour rates nationally |
| Wales | 0.95x | £55,000-62,000 | Lower labour, rural access costs |
Source: Mayfair Studio regional cost model (ConcreteMath + Costmodelling) • Data as of 2024/25 rates
Trade Cost Breakdown
A loft conversion involves multiple specialist trades. Labour typically accounts for 40-50% of total cost. Here are London day rates by trade, based on ConcreteMath 2024/25 data:
| Trade | London day rate | Typical days on loft | Total labour cost |
|---|---|---|---|
| Roofer | £300-450 | 8-12 | £2,400-5,400 |
| Carpenter / joiner | £275-400 | 12-18 | £3,300-7,200 |
| Electrician | £350-550 | 3-5 | £1,050-2,750 |
| Plumber (if adding bathroom) | £300-500 | 4-6 | £1,200-3,000 |
| Plasterer | £250-400 | 4-6 | £1,000-2,400 |
| Tiler (if adding bathroom) | £250-400 | 2-3 | £500-1,200 |
| Painter & decorator | £200-350 | 3-5 | £600-1,750 |
| Scaffolding | £150-250/week | 4-8 weeks | £600-2,000 |
| Skip hire | £300-500 each | 2-3 skips | £600-1,500 |
Source: ConcreteMath trade rate data • Data as of 2024/25
What Drives Loft Conversion Costs Up
The survey data reveals clear patterns in what pushes loft conversion costs above average:
- 1.Adding an en-suite bathroom adds £8,000-15,000 to the project. Plumbing, tiling, sanitaryware, and waterproofing all stack up. Soil pipe routing can be particularly expensive if it needs to run externally.
- 2.Structural complexity. Party wall awards (terraced/semi-detached), steel beams for open-plan layouts, and chimney breast removal all add cost. A party wall agreement alone can take 6-8 weeks and cost £1,500-3,000.
- 3.Staircase design. A standard straight flight is cheapest (£2,000-3,500). Winding or spiral staircases cost £5,000-12,000 and require more complex structural support. The staircase position also determines how much existing first-floor space you lose.
- 4.Planning requirements. If your loft conversion needs planning permission (mansard, or property in a conservation area), add £3,000-6,000 for planning fees, design development, and heritage assessments. Permitted development conversions avoid this entirely.
- 5.Fire safety. Building regulations require a protected escape route from the loft to the front door. In a three-storey house (ground + first + loft), this means fire doors on every room opening onto the staircase, mains-interlinked smoke/heat detectors, and sometimes a sprinkler system. Costs: £1,500-4,000.
Dormer vs Mansard: Which Is Worth It?
A rear dormer is the most common London loft conversion. It projects from the rear roof slope, creating a box-shaped room with full headroom. Cost: £88,000 London average. It usually qualifies as permitted development on houses (not flats, not in conservation areas).
A mansard conversion replaces the roof slope entirely with near-vertical walls and a flat or low-pitch top. It creates the maximum possible floor area but costs £110,000 in London and always requires planning permission. Mansards are common in inner London terraced houses where every square metre counts.
The decision comes down to value per square metre. A mansard creates roughly 30-40% more usable floor area than a dormer on the same property. At London property values of £7,000-15,000/m², that extra space can be worth £50,000-150,000 - making the £22,000 cost difference look reasonable. But only if planning is granted.
| Factor | Rear dormer | Mansard |
|---|---|---|
| Average cost (London) | £88,000 | £110,000 |
| Usable floor area added | 15-20m² | 20-30m² |
| Planning required | Usually PD (houses) | Always |
| Build time | 8-12 weeks | 12-16 weeks |
| Party wall needed | Sometimes | Usually |
| Best for | Most properties | High-value inner London |
Source: DesignForMe survey, Mayfair Studio analysis • Data as of 2025/26
Full Cost Breakdown: London Dormer Loft
Here's where the £88,000 London average actually goes:
| Item | Cost range | % of total |
|---|---|---|
| Structural work (steel, floor joists, dormer frame) | £18,000-24,000 | 20-27% |
| Roofing (tiles, felt, lead flashings) | £6,000-9,000 | 7-10% |
| Windows (dormer window + Velux rooflights) | £3,000-6,000 | 3-7% |
| Insulation (walls, floor, roof) | £3,000-5,000 | 3-6% |
| Electrics (lighting, sockets, consumer unit upgrade) | £3,500-5,500 | 4-6% |
| Plumbing (radiators, en-suite if included) | £4,000-12,000 | 5-14% |
| Plastering and internal finishing | £4,000-6,000 | 5-7% |
| Staircase | £2,500-5,000 | 3-6% |
| Flooring | £1,500-3,000 | 2-3% |
| Fire safety (doors, alarms, escape route) | £1,500-3,500 | 2-4% |
| Scaffolding | £2,000-4,000 | 2-5% |
| Architectural drawings and structural calculations | £3,000-5,000 | 3-6% |
| Building control | £500-1,200 | 1% |
| Party wall (if applicable) | £1,500-3,000 | 2-3% |
| Contingency (10%) | £7,000-9,000 | 10% |
Source: Mayfair Studio cost model, ConcreteMath trade rates • Data as of 2024/25 rates
Frequently Asked Questions
How much does a loft conversion cost in London in 2026?
A standard dormer loft conversion costs £88,000 on average in London, based on DesignForMe's 2025 survey of 1,500+ completed projects. Mansard conversions average £110,000. Velux (rooflight-only) conversions cost £55,000. These figures include structure, first and second fix, but not furniture or decoration.
Is a loft conversion cheaper than an extension?
Loft conversions and ground-floor extensions cost similar amounts per square metre in London (roughly £4,000-5,500/m² all-in). However, loft conversions often add more value because they create a new bedroom - which has a bigger impact on property value than enlarging a kitchen or living room. The key advantage is that most loft conversions don't require planning permission.
Do I need planning permission for a loft conversion in London?
Most rear dormer and hip-to-gable loft conversions qualify as permitted development on houses. You don't need planning permission unless you're in a conservation area, the property is a flat or maisonette, or you're building a mansard. Our free AI chat checks your specific property in 60 seconds.
How long does a loft conversion take?
A standard dormer loft conversion takes 8-12 weeks on site. Add 4-6 weeks for design and building regulations approval before work starts. Mansard conversions take 12-16 weeks on site because of the structural complexity. Party wall agreements, if needed, add 6-8 weeks to the pre-construction timeline.
Why are loft conversions more expensive in London?
London's 1.57x premium on standard loft conversions is driven by labour costs. Roofers charge £300-450/day in London vs £200-300 outside. Carpenters charge £275-400/day vs £200-300. Material costs are similar nationally, but transport and parking in London add 5-10% to material delivery costs.