The short answer
A flat-roof skylight or rooflight typically costs £800–£1,500 installed in the UK, depending on size, glazing and how complex the fit is. A simple flush flat-roof rooflight can be at the lower end, while larger units, triple glazing, walk-on glass or electric opening push toward and beyond the top. Flat-roof units differ from pitched-roof Velux windows because they sit on a kerb or upstand built up from the roof deck, so the price also depends on the upstand and weatherproofing, not just the glass. As with any rooflight, access and region move the figure, and a measured quote is the only way to be sure.
Flat-roof rooflights are a different product from pitched-roof Velux windows — they sit on an upstand and are common on extensions and dormers. Here is what they typically cost and why.
Typical flat-roof costs
- Flat-roof rooflight, fitted£800–£1,500
- Simple flush unitlower end
- Large / triple-glazed / walk-ontop end and up
- Sits ona kerb / upstand
- Extra driversglazing, opening, access
What a flat-roof rooflight costs
For a typical flat-roof skylight, budget £800–£1,500 installed. The lower end covers a smaller, fixed, flush rooflight on an accessible extension roof; the upper end reflects larger units, upgraded glazing (triple-glazed, solar-control or walk-on), or electric opening for ventilation. Because the unit sits on a kerb, the installer also builds or checks the upstand and weatherproofs around it, which is part of why flat-roof pricing differs from a pitched-roof window slotted between rafters.
| Item | Typical figure | Notes |
|---|---|---|
| Flat-roof rooflight, fitted | £800–£1,500 | size & glazing dependent |
| Simple flush unit | lower end | smaller, fixed, accessible |
| Upgraded glazing / opening | upper end+ | triple-glazed, walk-on, electric |
| Upstand / kerb work | included in fit | weatherproofing the opening |
Indicative UK figures for guidance. Sources: Checkatrade and trade cost guides.
Flat-roof vs pitched-roof units
On a pitched roof, a Velux-style window fits flush between the rafters, and pricing is driven by the unit and the access. On a flat roof, the rooflight sits proud on a kerb so water runs off, which means the upstand, flashing and membrane detailing all matter. That is why a flat-roof job can carry costs a pitched one doesn't, and why it is worth using an installer used to flat-roof detailing rather than assuming the two are interchangeable.
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Frequently asked questions
How much does a flat-roof skylight cost in the UK?
Typically £800–£1,500 installed, depending on size, glazing and complexity. A simple flush unit is at the lower end; larger, triple-glazed, walk-on or electric units sit at the top and beyond.
Why does a flat-roof skylight cost differently to a Velux?
Flat-roof rooflights sit on a kerb or upstand built up from the roof deck, so the price includes the upstand and weatherproofing, not just the glass. A pitched-roof Velux fits flush between rafters instead.
What pushes a flat-roof rooflight to the top of the range?
Larger sizes, upgraded glazing such as triple-glazed, solar-control or walk-on glass, electric opening for ventilation, and any extra upstand or access work.
Sources & further reading
Figures on this page are typical UK ranges drawn from published sources and depend on your specific property. They are guidance, not a quotation.