Do Roof Lanterns Make a Room Too Hot?

Sunlight carries heat. When it falls through a roof lantern, the floor and furniture absorb it and warm the room. A wall window gets the sun at a low angle for much of the day, but a roof faces the sky, so a lantern on a clear summer day catches strong sun for hours.

Warm air also rises. In a tall lantern, heated air collects at the top, under the glass, and has nowhere to go unless something opens. That is the part you can fix most easily.

The shape of the room plays a part. A tall kitchen extension with a high lantern holds a big volume of air above head height, so the warmth gathers up there and the living level stays more comfortable than you might expect. A low, compact room with a large lantern directly over a seating area feels the sun more, because there is less air to share it with.

The glass is the first decision. A solar-control coating reflects part of the sun's heat while still passing daylight, and it is the standard answer to a bright south-facing roof. Some glass also carries a faint tint. Self-cleaning coatings are separate, and they do not change heat gain.

Solar-control glass can look slightly less clear. Look at a sample in daylight at the survey, not just under shop lights. What the upgrade adds to a quote is covered under roof lantern cost.

Ask for the glass specification in writing, and keep it. If you later want to know why one room feels different from another, the specification is the first thing to check.

Which way the roof faces matters as much as the glass. A lantern on a north-facing extension may never get too warm. One on a south-facing extension that no tree or neighbouring wall shades will collect the most sun.

Shade can be added. External blinds or fabric pleated blinds sit under the glass or on a track and cut the heat before it reaches the room. Internal blinds help with glare, though they stop less heat because the sun has already passed through the glass by then. A neighbouring tree or a pergola may shade the roof during the hottest hours, but plan around what is there now.

On a tall lantern, a size change can also help. The guide to roof lantern sizes explains how a lower profile or a smaller footprint cuts the sun let in.

A house in the older parts of Bristol or Bath may already have trees and tall neighbouring walls. Those cast long shadows over a rear extension in the morning and evening, which spares the lantern the worst of the sun.

Vents are the part of this story that fits our approach most closely. A lantern with a sash that opens lets the warm air at its peak escape, and draws cooler air in through a door or window lower down. On a warm evening that can help a room cool, though it will not match what a mechanical system does.

Motorised vents can run from a wall switch or a remote, and a sash set in the lantern roof sits out of the way of furniture. The opening roof lantern page covers the types. For rooms that need a draught through, pair a lantern vent with a window or door that opens on the opposite side. Our guide to fresh air rooflights shows how that cross-flow works.

A vent also lets the room breathe overnight. A small gap left open in a safe position, using a vent bar or a restrictor, lets cooler night air in while the house is quiet.

A good survey will ask which way the roof faces, what shades it, and how you use the room. A kitchen and dining space used from early morning is different from a study used in the afternoon. Every quote shows the opening options, with the glass type written beside each, so the comparison is easy to make.

If you are adding a lantern to a flat roof you already have, the glass and vents still apply. Adding one over an old flat roof is dealt with in adding a lantern to an old flat roof. For the whole range, go back to roof lantern installation.

No glass choice is a guarantee of a particular temperature, and we do not quote figures. What we can do is match the unit to the roof and the room, so the lantern works with the way you live.

A change of glass can cut the heat too. Our guide to solar control glass for a rooflight explains how the coating works.