Velux window installation in existing roofs
Adding a roof window is one of the simplest ways to bring daylight into a loft room, a top-floor landing, a bathroom or a vaulted ceiling. This page is about fitting new roof windows into an existing roof, or replacing old ones, rather than converting a loft. ADB SW works on pitched roofs and interiors across South Devon. Send photographs of the roof and the room below, with an idea of where you want the light.
Choosing the position and size
A good position balances light, view and practicality. The window should sit between rafters where possible, at a height that lets you see out and reach the handle, and away from chimneys, valleys and other junctions that complicate the flashing. Roof pitch matters too, because each window and flashing kit is designed for a particular range of slopes.
Sizing often follows the rafter spacing. A window that fits between existing rafters avoids structural alteration; a wider window, or two side by side, means cutting rafters and adding trimmers to carry the load around the opening. Blinds, ventilation options and whether you want a top-hung or centre-pivot window are worth deciding before ordering.
What roof window installation involves
Roof window installation usually starts from outside. The slates or tiles are removed around the opening, battens and membrane are cut back, and any trimming is completed. The frame is fixed, the membrane collar and insulation collar fitted, and the manufacturer’s flashing kit installed to suit the roof covering, with the slates or tiles then reinstated around it.
Inside, the opening is lined, insulated and plastered, with the reveals splayed to spread more light into the room. Where the window sits in a ceiling rather than a sloping wall, a light shaft is built through the loft space. Decoration follows once the plaster has dried. Careful work at the flashings and the internal vapour control is what keeps the window dry and free from condensation.
Skylight installation in flat and vaulted ceilings
Skylight installation in a flat roof uses a different product, such as a fixed or opening flat roof light on an upstand, rather than a pitched roof window. Vaulted ceilings are usually straightforward because the window opens directly into the room. In both cases, the existing roof structure and insulation build-up determine how the opening is formed and finished.
Replacing an old roof window is often simpler than fitting a new one, especially if the new frame matches the existing opening. Where the size changes, the opening is adjusted and the flashings renewed. Older windows with failed seals or rotten frames can be swapped for better-insulated units without altering the room.
Approvals and getting a quote
Roof windows often fall within permitted development, provided they do not project significantly beyond the roof plane and, on a roof slope facing a highway, meet any applicable conditions. Conservation areas and listed buildings have tighter controls and may require conservation-style windows. Where rafters are cut or the work forms part of wider changes, building regulations may apply.
For an enquiry, send photographs of the roof outside and the room inside, the window size you have in mind and what the room is used for. ADB SW can discuss options and provide a written quote. If you are planning to turn the loft into a room, our Velux loft conversion page covers that work.
Common questions
How long does Velux window installation take?
A single window between rafters can often be fitted and weathered in a short visit, with internal plastering and decoration following. Trimming rafters, scaffolding or several windows extend the programme.
Do I need planning permission for a roof window?
Often not, under permitted development, but limits apply, and conservation areas or listed buildings may need consent. Building regulations may apply if rafters are cut.
Can a roof window be fitted in any roof?
Most pitched roofs can take one if the pitch suits the product and the position avoids awkward junctions. Very shallow pitches and some roof coverings need specific products.
What affects the cost of roof window installation?
The window size and type, whether rafters need trimming, access and scaffolding, the roof covering, and how much internal lining, plastering and decoration is required.
Tell us about your project
Send the property details and the work you have in mind so the scope can be discussed before a quote is agreed.