Where a stairwell rooflight fits in a Cambridge house
A staircase needs a flat or low-pitched roof directly above it, and in Cambridge homes that usually means a loft conversion, a rear addition or a single-storey house.
The commonest case is the loft. In the terraces around Romsey, Petersfield and Chesterton, the new stair to a loft room tends to climb up under the flat top of a rear dormer, and a rooflight set into that flat roof lights both the top flight and the landing outside the new bedroom. The same idea works where a two-storey rear addition has a flat roof over the stair, and in some newer homes at Eddington or Great Kneighton where the stair sits against a flat-roofed section of the plan. Our answer on adding a rooflight to a flat roof dormer covers that roof in more detail.
The rooflight goes in exactly as it would over any room: the joists are trimmed to form the opening, an insulated upstand is built at least 150mm above the finished roof, and the unit sits on that kerb with a fall on the glass. What changes is everything below the ceiling line, because the space underneath is a flight of stairs. The flat roof rooflight installation hub sets out the standard sequence.
Head height, the stair and the ceiling line
A rooflight sits above the ceiling, so it does not reduce headroom, but it will not rescue a stair that is short of headroom either.
Approved Document K asks for clear headroom of 2.0m over a stair, measured vertically from the pitch line of the treads. In a loft conversion there is some relief where space is tight: 1.9m at the centre of the stair, falling to 1.8m at the side, is generally accepted. Building Control measures to the lowest point above the stair, which is the ceiling or the edge of the trimmed opening, not the underside of the glass. The recess formed by the rooflight lining gives welcome extra height to the eye, and it feels generous as you climb, but you should not count on it to meet the numbers. If the stair only works with the rooflight recess, talk to your designer and the Building Control surveyor before the unit is ordered.
The edges of the opening need thought too. A trimmer joist or a lining corner that projects over the top few treads is exactly where heads get knocked. We line the reveal so its lowest edge sits clear of the walking line, and where the structure allows we splay the lining outward so the opening reads as wider from the stair.
Safety glass over a staircase
Glass above people who are moving, and above a stair in particular, should have a laminated inner pane, so that a broken pane is held in place instead of falling.
That is the usual specification for any overhead glazing, and it matters more over a stair, where someone could be carrying a child or a laundry basket at the moment something strikes the glass. A toughened outer pane takes the knocks from hail and from feet during roof maintenance; the laminated inner layer is the one that keeps the stair safe. Quality flat rooflights offer this build as standard or as a listed option, and our guide to flat rooflight glazing choices shows how it combines with low-E and solar control coatings.
| Choice | Why it helps over a stair |
|---|---|
| Laminated inner pane | Holds broken glass in place above the flight |
| Solar control coating | Cuts heat that gathers at the top of the stairwell |
| Self-cleaning outer pane | Less need to reach glass you cannot easily get to |
| Warm-edge spacer | Warmer glass edge where rising moist air meets it |
Fire is a separate point. In a loft conversion the stair becomes the escape route from the new floor, and Building Control looks at that route as a whole. A rooflight above the stair is part of the roof, not the stair enclosure, so it does not usually conflict with a protected stair, but it still has to stay out of the 1500mm zone either side of a party wall. Our answer on how close a rooflight can be to a party wall explains why, and on a narrow terrace that zone can decide where the stair light can go.
Reaching it: opening, cleaning and blinds
A rooflight over a stairwell can sit five or six metres above the lowest tread, so anything you might want to do with it has to work without a ladder.
That makes the choice between a fixed and an opening unit more interesting than usual. A stairwell behaves like a chimney: warm air rises through the house and collects under the roof. An opening rooflight at the top lets it out, and on a warm Cambridge evening it draws cooler air in through the windows downstairs. That only works if you can open it, so over a stair an opening unit should be electric, with a wall switch or remote and a rain sensor that closes it when the first drops land. Our guide to fixed vs opening flat rooflights compares the two.
- Cleaning: the outside is cleaned from the roof, and a self-cleaning coating lengthens the gaps between cleans.
- Shading: a blind you cannot reach needs to be motorised or sealed between the panes, as set out in our answer on integral blinds.
- Condensation: the moist air that rises up the stair meets the coldest surface at the top, so the vapour control layer must be carried up to the frame.
What the light does to a landing and hall
Light from above a stair lands first on the top landing, then washes down the stairwell walls, and reaches the hall as soft, reflected daylight.
How far it travels depends on the shaft. A pale, smooth stairwell wall acts as a reflector, and a light well with a splayed lining spreads the light wider than a straight-sided one. On a grey day, or under a north-facing sky, you get an even glow down the whole flight, which is often all a dark terrace hall needs. With a south or west aspect the sun throws a bright patch that moves across the stair through the afternoon. That is lovely on a landing, but a sharp sun patch across the lower treads can dazzle someone coming down, and a solar control pane or a diffusing blind softens it.
This is where we look at the room rather than the roof. At the survey we check where the sun patch will land on the treads at different times of year and where the light will help the landing most, then set the position and glass to suit. Our guide to positioning a flat roof skylight covers placement in general, and how we plan the light explains the method. You can book a light survey to have it worked out for your stair.
Questions people also ask
Can you put a skylight above a staircase in a loft conversion?
Yes, and it is a sensible place for one. The stair usually rises under the flat roof of the dormer, so a flat rooflight there lights the top flight and the new landing. Headroom must still meet Part K without relying on the rooflight recess, and the unit should have a laminated inner pane.
Does a rooflight over the stairs need Building Regulations approval?
A new rooflight generally does, because it affects the structure, the thermal performance and, in a loft, the escape route. Where the work is notifiable we handle the Building Control notification as part of the installation.
Will a rooflight make the stairwell hot?
It can, because heat gathers at the top of the stair. Solar control glass limits the gain, and an opening electric rooflight lets the warm air escape, which helps the whole house on a hot day.
How do you clean a rooflight above a stairwell?
From the roof, not from the stair. A self-cleaning outer pane helps with dust and light dirt, and the inside needs cleaning only now and then, usually with a long-reach pole or when the stairwell is decorated.
