How Much Does a Loft Conversion Cost Per m² in 2026? (UK)
A UK loft conversion in 2026 typically costs £1,150–£2,600 per m² fitted. A simple rooflight (Velux) conversion runs £1,150–£1,500 per m²; a dormer conversion is £1,500–£2,100 per m²; a hip-to-gable reaches £1,900–£2,500 per m²; and a mansard the most at £2,200–£3,000 per m². A typical 25–30m² dormer conversion comes in around £40,000–£65,000 all-in.
Loft conversion cost per m² by type (2026 UK)
The single biggest driver of loft conversion cost is the conversion type, because it dictates how much structural and roofing work is involved. As a 2026 UK guide, per m² of new floor area: rooflight / Velux £1,150–£1,500; dormer £1,500–£2,100; hip-to-gable £1,900–£2,500; mansard £2,200–£3,000. Figures assume insulation to current Part L, plasterboard finish, a fixed staircase, double-glazed windows and full building control sign-off.
Typical total cost by size
Most usable loft rooms are 20–35m². On a mid-range dormer basis: a small 18m² single-room conversion is roughly £28,000–£40,000; a standard 25m² dormer £40,000–£55,000; a large 30–35m² master suite with en-suite £55,000–£75,000+. A rooflight conversion on the same footprint saves 20–30% but only works where you already have generous head height under the existing ridge.
What adds to the headline figure
Beyond the per-m² rate, the common extras are: en-suite shower room £4,500–£8,500; steel beams / RSJs £1,800–£3,500 including structural calcs; new staircase £1,500–£3,500 depending on joinery; dormer windows or Juliet balcony £2,000–£3,800; and rooflights £1,500–£2,500 fitted each. Fire-safety upgrades (mains-linked alarms, fire doors to the escape route) are mandatory and usually £800–£1,500.
Planning permission and building control
Many rear-facing loft conversions fall under permitted development provided the added roof volume stays within 40m³ for terraced houses or 50m³ for semi-detached and detached, and nothing extends above the existing ridge. Front dormers, conservation areas, Article 4 zones and flats always need planning permission. Building control approval is required for every loft conversion regardless of planning — it signs off structure, insulation, fire escape and stairs.
How to budget step by step
1. Measure the usable floor area
Only count space with at least 1.5m head height. Cost scales at roughly £1,150–£2,600 per m² fitted.
2. Choose the conversion type
Rooflight is cheapest, mansard the most expensive. Head height under the ridge decides whether a cheaper rooflight is even possible.
3. Add the extras
En-suites, steel beams, staircases and dormers are where budgets over-run.
4. Compare three matched quotes
FMB or TrustMark members, on the same written scope including building control.
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