How Much Does a Velux Loft Conversion Cost in 2026? (UK)
A Velux loft conversion — also called a rooflight conversion — in 2026 UK costs £22,000–£38,000 fully finished. It's the cheapest loft conversion type because the existing roof shape stays unchanged: no dormer, no mansard, no major roof structure work. The cost driver is floor area, staircase route, insulation upgrade and the number of Velux windows. A simple 18m² Velux loft on a 1960s semi sits at £22,000. A 32m² Velux master bedroom-plus-ensuite in a Victorian terrace pushes £38,000+. This guide gives the 2026 cost ladder, the 6 line items every fair quote should show, and the PD eligibility checklist.
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The 6 Things That Drive Velux Loft Conversion Cost
1. Usable floor area
Headroom over 1.5m drives usable area. 1960s trussed roofs lose 40–60% to truss replacement. Cut-rafter Victorian roofs give 80%+ usable area at far less cost.
2. Staircase route
Easy: straight run over the existing stairs (£900–£1,800). Hard: stealing space from a landing or bedroom (£2,400–£4,200). Spiral or alternating tread: £3,000–£5,500.
3. Number & size of Velux
Standard sizing: 78×118cm at £550–£950 supply & fit. Large 78×140cm runs £750–£1,200. Most Velux conversions use 2–4 windows; budget £2,000–£4,500.
4. Insulation upgrade
Building Reg L1 sets minimum U-value 0.18 on roof slopes. PIR between & under rafters adds £2,200–£3,800 — but cuts heating bills 10–14%.
5. Bathroom or ensuite
Adding an ensuite is the biggest single cost step: £6,500–£12,000 for a full shower-room with macerator or saniflo. Halves your bathroom queue, sells the conversion.
6. Building Regs & structural
Structural engineer £600–£900 for steel beams & calcs. Building control fees £700–£1,200. Fire-rated doors and protected stair are mandatory.
Common Questions
Related Guides
More guides in Costs.
Velux / rooflight — guides and detail
The detail behind the number: what changes the price, the planning position, and how to check a quote before you accept it.
Registered members: Loft Conversions
12 businesses offering loft conversions have a public profile with BestBuilders. Each listing is a business that registered with us directly; the details shown are the ones it declared at registration, and a Companies House number appears only where one was given.
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