The short answer
It can, if the lantern is plain clear glass, faces the midday sun and has no way to let warm air out. Sunlight passing through glass turns into heat inside the room. A solar control coating, a sensible position, opening vents at the top and a blind underneath keep a lantern kitchen comfortable through a south east summer afternoon.
Where the heat comes from
A lantern does not make heat. It lets the sun's heat in, and then the room has to lose it again.
Short-wave sunlight passes through clear glass almost unhindered. It lands on the floor, the worktops and the furniture, which warm up and give that energy back as long-wave heat. Glass is poor at letting long-wave heat out again. That is the same effect that warms a greenhouse, and it is why a room under a lantern can feel warmer than the rest of the house on a bright day even when the air outside is mild.
Two features of a lantern make the effect more noticeable than with a small flat rooflight. The first is area. A lantern over a kitchen extension is often one of the largest pieces of glass on the house, so more sunlight arrives at once. The second is height. Warm air rises, and the raised box of a lantern gives it somewhere to collect above the ceiling line. Without a vent, that trapped layer slowly warms the room from above.
None of this is a reason to avoid a lantern. It is a reason to specify one for the heat as well as the light, which is what the rest of this page covers.
Four things that decide how warm it gets
Most of the variation between a comfortable lantern and a stuffy one comes down to these four choices, and only one of them is the glass.
The coating on the glass
Solar control glass carries a thin metallic coating, applied to one of the inner faces of the sealed unit. It reflects part of the sun's energy back out before it reaches the room, while still passing most of the visible light. Manufacturers describe this with a g-value, the share of solar energy that gets through. A lower g-value means less heat arriving. The trade-off is a slight tint in the daylight, and a lantern with a strong coating looks a touch cooler in tone than a clear one. Compare the options against your own room rather than a brochure. Our answer on choosing the best glass for a roof lantern puts the coating beside the other glass choices.
Which way the lantern faces
The lantern's ridge runs in a fixed direction, and its panes face all four ways. A south facing pitch takes the strongest sun at the hottest part of the day. A north facing pitch gives steady daylight and very little heat. Shade from a neighbouring tree or a taller part of the house changes the picture again. We cover this in more depth in roof lantern orientation and the summer sun.
Whether warm air can leave
This is the choice people forget. A fixed lantern traps the warmest air at its peak. A lantern with opening vents lets that air out, and cooler air is drawn in from a door or window lower down to replace it. The taller the lantern, the stronger the pull. See how a lantern can have opening vents for the options, or our electric and opening rooflight installation page for motorised units that can be tied to a rain sensor.
What hangs underneath
A blind stops sunlight reaching the room, and that is more effective than trying to cool the room afterwards. A blind fitted inside the lantern still lets the glass absorb heat, but it keeps it off your head and your table. External shading is stronger still, though less common on a lantern. There is more in lighting and blinds around a roof lantern.
What each measure does, side by side
The measures work differently, and they suit different rooms. This table sets them out plainly.
| Measure | What it does | Watch for |
|---|---|---|
| Solar control coating | Reflects part of the sun's energy away | Slight tint in the light |
| Opening vents | Lets the warm layer out at the peak | Needs an inlet lower down |
| Internal blind | Shades the room directly | Glass still warms above it |
| Careful positioning | Reduces the sun on the largest panes | Decided before the lantern is ordered |
No single row does everything. A coating with no vent still builds up warm air. A vent with clear glass still lets a great deal of sun in. The two together, with a blind for the brightest weeks, is the combination that reads well in a kitchen.
Keeping the glass cooler without making the room dim
The fear is that solar control turns a bright room into a dull one. A sensible build avoids that.
Modern coatings are chosen to pass a high share of visible light while turning away a larger share of the heat. The result is a room that looks bright and feels a little calmer. If you want to understand what you are giving up, ask to see a sample pane against the sky, held up at the survey rather than judged from a sheet of figures.
The regulations sit behind this as well. Part L of the Building Regulations limits how much heat a lantern loses, and Part O deals with overheating in new homes. A large glazed roof on a new extension still has to be specified with solar gain in mind, and the coating is the usual way to do it. Our page on whether roof lanterns are energy efficient enough for Part L covers the winter side of the same glass.
How we decide for your kitchen
We look at the room and the roof together, before the glass is chosen.
At the survey we note the direction of the sun, the size of the opening, how the room is used and where a cooling draught could come from. A kitchen that is busiest at lunchtime with the back door open is different to a home office shut away behind a closed door. Those answers decide the coating, the vents and whether a blind is worth building in from the start.
The choice goes into the quiet spec that comes with every quote. Heat and sound are linked in that document, because a vent that cools a room is also an opening for noise, and the glass build has to hold both in balance. Planning a lantern over a new extension? Our note on a roof lantern over a kitchen extension sets the heat question in the wider brief.
Heat questions people ask about lanterns
Will a lantern be colder in winter as well?
Not if the unit is specified properly. A modern sealed double unit with a low emissivity coating and a warm edge spacer keeps the room warm, and many lanterns lose less heat than an older flat rooflight. The frame and the upstand matter as much as the panes.
Is a lantern hotter than a flat rooflight?
Not by nature. What matters is the glass area, the coating and the ventilation. A large lantern admits more sun than a small flat rooflight simply because it is bigger. Our comparison of a roof lantern and a flat glass rooflight sets out the differences.
Can I add a coating to an existing lantern?
The coating is part of the sealed glass unit, so it cannot be added to the pane afterwards. The lasting answer is to renew the glass units, or the lantern, with solar control glass. A blind will help in the meantime.
Do vents let rain in?
Opening lantern vents are built to shed water when closed, and motorised versions can close themselves when rain is detected. Sizing and sensors are covered when you get a quote.
The full service, from survey to handover, is on our roof lantern installation page.