The short answer
Fixed glass on a well-made kerb suits a room that only needs light. If the room needs air, an opening unit with a rain sensor is worth the extra; where you want to see the sky from inside, a larger pane gives a better view; and if you need a floor of glass, walk-on glass is the only choice. A lantern is a different shape of rooflight and suits a deeper room.
- Free survey, fixed written quote
- 10-year workmanship guarantee
What the room needs from a skylight
A hall or a landing wants light from above and little else, so a fixed pane is enough. A shower room wants to clear steam, which points to an opening unit. A rear bedroom under a flat roof wants curtains or a blind, and a unit with a built-in blind or a tinted pane may cover that.
The roof narrows the list. A narrow strip of roof between two parapet walls limits the width of the unit, and a roof with a sharp fall may need a taller kerb on its low side. Our guide to rooflight upstands and kerbs explains how that height is worked out.
| The room needs | Look first at |
|---|---|
| Light only, no maintenance | Fixed flat rooflight |
| Fresh air or steam control | Manual or electric opening rooflight |
| A glass floor or path | Walk-on rooflight |
| Height and sky from every side | Roof lantern |
| Light into a windowless corridor | A sun tunnel, where the roof is small |
Glass, frame and kerb
Glass for a flat roof brings specifics of its own. Double glazing is standard, and a laminated inner pane is a choice for rooms where a fall of glass would be a worry. Solar-control coatings cut heat gain on a south-facing roof, and self-cleaning coatings help where leaves collect. A new rooflight is held to 2.2 W/m²K under Part L for existing dwellings, and a frame with a thermal break helps meet it.
The kerb deserves as much thought as the glass. An insulated kerb built for the unit keeps the roof warm round the edge, and the membrane is dressed up its face so that rain cannot reach the joint. We specify the kerb with the unit, since the two are priced and fitted together.
Fixed, manual or electric
A manual opening unit lifts on a hinge and is worked with a pole or a handle, which suits a shower room or a utility within reach. An electric unit runs from a motor, often with a rain sensor, and makes sense where the ceiling is high or the roof is awkward to reach. Both bring a wiring or hinge detail that a fixed unit does not have, so we ask who will be using the switch before we recommend one. Our electric opening rooflights page sets out how those units are powered.
Size and position on the roof
A big pane is not always better. Over a small utility room, a rooflight that fills the ceiling can overheat the room in July, and one that is too small leaves corners dim. We mark the outline on the floor with tape at survey so you can stand in it and see where the light will land.
Position follows the room's use. Over a worktop, the light falls on the task; over a sofa, it falls on the seating. In a bedroom, a unit set towards the window wall gives light without shining on the bed at dawn.
If the roof is accessible, glass may need a pass for foot traffic or a guard. Walk-on units are specified for the load they carry, which our walk-on rooflights page covers.
Edges matter as well. A unit pushed close to a parapet leaves a narrow gutter of membrane that is hard to dress and slow to dry. A hand's width or more between the kerb and any wall gives the roofer room to work and the water room to run, and we plan that gap on the drawing before the glass is ordered.
Where a roof has existing pipes, a vent stack or an extractor outlet, the unit has to sit clear of them with room for the kerb. Moving a soil vent is a plumber's job, and it is better to learn that at survey than on the morning the roof is opened. Tell us about any pipe you can see on the roof, or any boiler flue nearby.
Rules and the next step
A flat rooflight on a low kerb may fit within Class C permitted development if it sits no more than 150 mm above the original roof, though kerb and frame together can exceed that, so we measure it. Flats and maisonettes have no householder rights. The flat roof skylight planning guide sets out the rest.
Prices depend on size, glass, opening and the roof under it; see what a flat roof skylight costs. To choose for your own roof, see our answer on fitting skylights to a flat roof, or book a free survey and get a fixed written quote.
