In brief
The price of a fitted flat rooflight is set by five things: the size of the unit, whether it is fixed or opens, the glazing specification, the kerb it sits on and how easily the roof can be reached. No two flat roofs are quite the same, so a free survey comes first and a written quote follows. It lists each part so you can see what you are paying for.
- Size: a larger unit means more glass, a heavier frame and a bigger opening to form
- Fixed or opening: a vent, a motor and a rain sensor each add to the unit
- Glazing: the number of panes, coatings and the finish on the glass
- The kerb: new timber upstand, insulation and the covering turned up its sides
- Access: how the glass reaches the roof and what has to be set up to lift it
Size and the way the unit opens
A flat roof gives no standard fitted figure, because every roof is built differently and the same glass can need very different work around it. The page on rooflight costs explains how our pricing works across all products.
Size does most of the work. A wider and longer opening needs more glass, a sturdier frame and heavier lifting, and the kerb and trimming around it grow with it. Very large units may need more than one person on the roof and extra lifting equipment, which is worked into the quote.
A fixed rooflight is a sealed unit in a frame, and it is the simplest option. An opening rooflight adds hinges, a vent mechanism and sometimes an electric motor. Electric versions need a cable run and a controller, and many have a rain sensor that closes the vent when it starts to rain. Each of these adds to the price of the unit and to the electrician's first-fix work.
A walk-on unit is built with thicker laminated glass to take the weight of a person, and that is reflected in its price too.
The glazing specification
The make-up of the glass changes what the unit costs and how it behaves. A double-glazed sealed unit is the baseline. Triple glazing improves thermal performance. Solar control coatings reduce heat gain in a south-facing room. Self-cleaning coatings and toughened or laminated panes each add to the price, and the inner pane is often laminated so that it holds together if it breaks.
Current Building Regulations set a limit for the heat lost through a rooflight in an existing home, so the glazing has to meet that figure. We tell you which specification we have priced and why. If you would rather see two options side by side, we can quote both and you can choose.
The kerb and the roof covering
A flat rooflight sits on a kerb, which is a raised upstand that lifts the unit clear of standing water on the roof. In a new build the carpenter forms it from timber, the roofer insulates and covers it, and the cost is shared between those trades. The kerb height and construction are covered in the upstand height guide.
The roof covering also matters. EPDM, GRP and felt each have their own method for turning the covering up the kerb and sealing against the frame, so the roofer's time varies with the material. If the roof is already finished and the rooflight is added afterwards, the covering has to be cut, lapped and made good, which is described in adding a rooflight to a finished roof. The sequence means one visit from the roofer if it is planned, and two if it is not.
Access to the roof and the finish inside
Getting glass to the roof is part of the price. A single-storey extension at the back of a house, reached from the garden, is easy to work on. A first-floor flat roof over a narrow side return, or one with scaffold already up for other trades, can alter the equipment and the time needed. The quote states the access we have allowed for.
Inside the room, the opening needs lining, usually with plastered reveals or a flat plasterboard return. If the plasterer is already working on the building, the reveals fit into their programme. If you want lighting set into the reveal, the electrician runs the cable at first fix. We agree who does each part with the people on site so no work is paid for twice.
Questions to put to any quote you receive
Quotes for the same rooflight can look far apart when they cover different things, so it helps to check what each one includes before comparing totals.
- Does it name the exact unit, with its size, glazing and whether it opens?
- Does it say who builds the kerb, and who insulates and covers it?
- Is the roof covering made good up the upstand by someone who works with that material?
- Is the lead time named, and who places the order?
- Are access, lifting and the inside lining included or left out?
A quote that answers each of those leaves little to be added later. One that is silent on them usually leaves the gap to be filled once the work has started. Asking these questions early costs nothing and makes two quotes much easier to compare.
From survey to written quote
The survey is free. We measure the opening, look at the roof construction and covering, and talk through the options for size, opening and glass. If your build is still on paper, a price can be based on the drawings and checked against the roof afterwards.
Your quote lists the unit and its glass, how long delivery will take and whatever the builder must supply. The maker decides that lead time, so it is stated up front and checked again at the order. If the kerb is to be built by someone else, we send the sizes in writing before the roof deck goes on. For the full range of products and what each involves, see our flat roof rooflights page.
