How much does a loft conversion cost in the UK?

In 2026, typical costs are: Velux/rooflight conversion £1,200-£1,500/m², rear dormer £1,500-£2,000/m², hip-to-gable with dormer £2,000-£2,500/m², and mansard £2,500-£3,000/m². A typical 20m² dormer conversion costs £30,000-£40,000 excluding bathroom.

What is included in loft conversion cost per m²?

The per m² rate typically includes structural works (steel beams, floor strengthening), insulation, plasterboarding, electrics, staircase, fire doors, building control fees and basic decoration. It usually excludes the bathroom fit-out, which adds £4,000-£8,000 depending on specification.

Which type of loft conversion is cheapest?

A Velux (rooflight only) conversion is cheapest at £1,200-£1,500/m² because it doesn't alter the roof structure. However, usable floor area may be limited by head height. A rear dormer adds more space but costs £1,500-£2,000/m². The best value depends on your roof type and head height.

Do I need planning permission for a loft conversion?

Most loft conversions can be done under Permitted Development rights without planning permission, provided they stay within volume limits (40m³ for terraced/semi, 50m³ for detached), don't extend above the ridge, use matching materials, and side-facing windows are obscure glazed. Mansard conversions usually need planning permission.

How long does a loft conversion take?

A typical rear dormer conversion takes 8-12 weeks from start to completion. Velux conversions are quicker at 4-6 weeks. Hip-to-gable and mansard conversions take 10-14 weeks. Allow additional time for party wall agreements (6 weeks) and building control sign-off.

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Loft Conversion Cost Calculator — UK Price Estimates 2026

Estimate loft conversion costs per m² for Velux, dormer, hip-to-gable and mansard conversions including bathroom, staircase and contingency.

Floor Area

Usable floor area of conversion

Conversion Type

£1500-£2000/m²

Bathrooms

En-suite or shower room

Custom Price/m² (optional)

Override default cost range

How We Calculate This

This calculator estimates loft conversion costs based on floor area and conversion type using current UK market rates.

The formula

Build Cost = Floor Area × Cost per m²

Total = (Build Cost + Bathroom + Staircase) × (1 + Contingency%)

Cost ranges (2025/26)

Velux: £1,200-£1,500/m²
Dormer: £1,500-£2,000/m²
Hip-to-gable: £2,000-£2,500/m²
Mansard: £2,500-£3,000/m²

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Verify with your supplier.