The lowest-cost and least disruptive conversion — but only if the roof already has the height.
Arrange a site visitA Velux or rooflight conversion — Velux is a manufacturer, and the name has become shorthand — converts the loft without altering the shape of the roof at all. Windows sit flush in the existing slope. Everything else happens inside: a new floor structure, insulation, a staircase, electrics, heating and plaster.
Because the roof is not extended or rebuilt, it is the lowest-cost conversion by a clear margin, the quickest, and the least likely to need a planning application. It is also the one with the strictest entry requirement, because it gives you nothing you did not already have in terms of height.
This is the whole question. Measure from the top of the existing ceiling joist to the underside of the ridge. As a working rule you want around 2.2m before anything starts — the new floor builds up from below, the insulation comes down from above, and the finished room still has to keep roughly 2m of headroom over the stairs.
If you have that height, a rooflight conversion is very likely the right answer and you should be sceptical of anyone selling you a dormer you do not need. If you are meaningfully short of it, no amount of clever detailing recovers the difference, and a dormer or hip-to-gable is the honest recommendation rather than an upsell.
Rooflight conversions generally fall within permitted development, provided the windows do not project more than 150mm beyond the plane of the existing roof slope and nothing sits higher than the highest part of the roof. Conservation areas and listed buildings are the usual exceptions, and on the principal elevation facing a highway the position is different again.
Building Regulations approval is still required. The requirements do not soften because the conversion is modest: you still need a protected escape route with fire doors, mains-linked alarms, a compliant staircase, an adequate floor structure and insulation meeting current standards.
Published UK guides put rooflight conversions at roughly £15,000 to £30,000 in 2026 — national averages rather than our quotes. Four to six weeks on site is typical, and because there is no structural work to the roof envelope the disruption is largely internal. The staircase opening is usually the most intrusive single element.
A short site visit tells us the roof type, the head height and where the stairs can land — which is most of what decides the design and the price. We will tell you if a conversion is not the right answer for your house.
Arrange a site visitAll loft conversions