Roof window installation: what it costs and what's involved
Fitting a roof window is a structural job as much as a roofing one. The window itself is often the smaller half of the cost.
The structural part
Rafters have to be trimmed and headers doubled so the opening doesn't weaken the roof. On modern trussed roofs this needs care, and on wider openings it needs designing rather than improvising.
The flashing kit matters
Every roof covering has a matching flashing kit — plain tile, profiled tile, slate, and low-pitch variants. Using the wrong kit is the most common cause of a leaking roof window.
Internal finishing
Plasterboarding and finishing the reveal is a separate trade cost. Straight reveals are cheaper; splayed reveals that throw more light into the room take longer.
What changes the price
Window size and glazing spec, roof covering, pitch, whether the loft is a habitable room already, and access. A blank slate roof at height is dearer than an interlocking tile roof on a bungalow.
Sensible pairing
If a slope is being stripped for a re-roof, that's the cheapest moment you will ever get to add roof windows.
FAQs
New openings in a roof usually engage building regulations for structure, and for habitable loft conversions there are additional requirements. We'll flag it before work starts.
Yes, with the slate-specific flashing kit. The detail differs from tiles and needs the correct recessed or standard kit.
A straightforward single window is typically a day for the roof side, plus internal finishing.
Related reading
More on costs & budgeting and the jobs that usually come with it.
- Dormer roofs: repair, re-cover and what it costsCosts & budgeting
- Flat roof cost: GRP versus EPDM versus feltCosts & budgeting
- Chimney repair costs: repointing, re-flaunching and rebuildsCosts & budgeting
- Roof warranties and aftercare: what's actually coveredProcess & paperwork
Looking for something specific? See our roofing services, cost guides, common roof problems or the areas we cover.
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