Velux · Rooflight · Lowest-cost loft conversion
The lowest-cost, quickest loft conversion, for roofs with good existing headroom. No change to the roof structure and usually no planning application.
A Velux (rooflight) loft conversion in London costs about £28,000–£45,000 in 2026 and takes 4–6 weeks on site. It needs around 2.2 m of headroom, is usually Permitted Development, and suits a bedroom or office more than a large suite.
Last updated 3 October 2026
A Velux conversion fits rooflight windows into the existing roof slope and strengthens the floor, adds insulation, a staircase and fire protection, without altering the roof structure. Because there is no dormer or rebuild, it is the quickest and lowest-cost way to turn a loft into a habitable room. The trade-off is floor area, since the sloping roof limits where you can stand upright.
If you need more floor area or a bathroom, compare a rear dormer or a hip-to-gable on a hipped roof.
Rooflights are normally Permitted Development provided that:
Building Regulations still apply, including fire safety, structural strengthening of the floor, insulation and a compliant staircase.
| Specification | Typical build cost | What you get |
|---|---|---|
| Standard Velux conversion | £28,000–£45,000 | Strengthened floor, rooflights, stair, insulation, electrics, Building Regs sign-off |
| Higher-specification Velux conversion | £45,000+ | More rooflights, built-in storage, shower room where space allows |
Figures exclude VAT and professional fees. Estimate your own figure with the Loft Conversion Cost Calculator.
Headroom and structure survey and layout options.
Structural calculations, Building Regulations and party wall notices where needed.
Floor strengthening, rooflights, stair, insulation, first fix and finishes.
Snagging walkthrough, Building Control completion certificate and handover.
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In 2026 a Velux (rooflight) conversion typically costs £28,000–£45,000 at standard specification. It is the cheapest loft conversion because the roof structure is not changed, but it needs enough existing headroom.
Usually not. Rooflights are normally Permitted Development if they do not protrude more than 150 mm beyond the roof slope, are no higher than the highest part of the roof, and side-facing windows are obscure-glazed and fixed or at least 1.7 m above the floor. Conservation areas, flats and listed buildings need planning permission.
Around 2.2 metres from the top of the floor joists to the underside of the ridge. Below that a dormer or mansard is normally needed to create usable height.
Usually about 4–6 weeks on site, after a few months of drawings, structural calculations, Building Regulations and party wall notices.
Sloping ceilings reduce the usable floor area, so you get less space than with a dormer, and a bathroom is harder to fit. It suits a bedroom, home office or playroom better than a large suite.
Cost figures are indicative 2026 London ranges for planning purposes, build cost only and excluding VAT, professional fees and fittings. They are not a quotation. Planning and Permitted Development rules depend on your specific address, so always confirm with your local council or a Certificate of Lawfulness.
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