The short answer
They can, but it depends on the glass, the direction of the slope and whether the unit opens. A large south-facing rooflight in clear glass will heat a room on a sunny afternoon. The right specification, with solar control glass, an opening unit and sensible shading, keeps it comfortable.
Why a rooflight can overheat a room
If you have wondered whether a rooflight too hot in summer is a real risk, the honest answer is yes, for the wrong combination. Sunlight arrives through a rooflight from above, for longer hours than it reaches a wall window, and it lands on floors and furniture that store the heat. Warm air then rises and gathers under the roof, where it stays unless it can escape.
The problem is not the glass alone. It is the combination of strong sun, a large area, no way for hot air to leave and a room that traps warmth. Change any one of those and the result changes with it.
What makes it better or worse
Look at these factors in your own house, because they decide how a given rooflight behaves.
- Direction. South and west slopes take the strongest sun. North slopes take almost none.
- Size. A bigger pane lets in more energy. A roof lantern or wide flat rooflight over an extension is a bigger source than a small roof window on a landing.
- Glass type. Clear glass lets most of the sun's heat through. Solar control glass turns part of it away.
- Ventilation. An opening unit lets hot air out at the top of the room. A fixed one cannot.
- The room beneath. A room with heavy floors and walls absorbs heat slowly. A light timber extension heats fast.
Time of day matters too. A south-facing slope in Coventry gets its worst sun around midday and early afternoon, while a west-facing one peaks in the early evening, just when you want to relax. If the room feels hottest at tea time, look at the west-facing glass first. Small habits help as well: closing blinds before the sun reaches the pane keeps the heat out, which is easier than clearing it once it is inside. Where a rooflight sits over a kitchen, cooking adds its own heat, so an opening unit above the hob area earns its keep.
The fixes that work
There is no single cure, but a few measures do most of the work, and they combine well.
- Solar control glass. A coating on the outer pane reflects part of the sun's heat before it enters. Our guide to solar control glazing explains how to choose one without darkening the room.
- An opening rooflight. Opened by hand or by electric motor, it lets warm air rise out. With a low window or door open elsewhere in the room, you get a flow of fresh air through the space. A rain sensor closes an electric unit if it starts to rain.
- External shading. A blind outside the glass stops the sun before it becomes heat. An internal blind helps with glare but the heat has already come in.
- Orientation-aware choices. A modest rooflight on a shaded or north slope may be all a room needs.
Is a skylight overheating problem fixable on an existing unit?
Often it is. If the frame is sound and only the glass is the weak point, a new sealed glass unit with a solar control coating can be put in the existing frame. Changing only the glass is not a controlled fitting under the Building Regulations. If the whole rooflight or roof window needs replacing, for example to add an opening function, that is notifiable building work, and Part L governs the new unit. A replacement in a pitched roof needs band B on the Window Energy Rating scale or a 1.4 W/m²K figure, while a flat-roof rooflight or lantern is held to 2.2 W/m²K. Building Control is told by us, not by you.
What we look at on a survey
On the free survey visit we note which way the slope faces, how big the opening is, any shade from trees or neighbouring roofs, and what the room is used for. A conservatory-style extension in Coventry with a south-facing lantern is a different case from a loft bedroom with a small north window. You then receive a fixed written quote naming the glass and the opening arrangement, so nothing changes on the day.
The new unit is flashed and sealed on the roof. Inside, the reveal is splayed where there is depth to do it, then plastered. That lining also improves the way light spreads and helps hide the unit from direct glare. The work meets current Building Regulations and is backed by our 10-year workmanship guarantee.
If you are weighing up a rooflight for a room that already runs warm, tell us at the survey. It changes what we recommend, and we would rather size and position the unit around the problem than add glass and hope.
Winter is the other half
A rooflight that is comfortable in July must still hold warmth in January. The two aims are compatible when the glass pairs solar control with a low-emissivity layer. Our answer on whether rooflights lose heat in winter covers that side of the question.
