Will a roof lantern make my room too hot?
Why roof glazing gains heat, and the four things that keep a lantern room comfortable: glass, size, ventilation and shading.
It can, if the lantern is large, the glass is ordinary and the room has nowhere for warm air to go. Roof glazing sees the sun when it is highest and strongest, so it gains more heat in summer than a wall window of the same size. The fix is to plan for it.
1. Choose solar-control glass
This is the most effective single step. A lower g-value stops much of the heat at the roof while still letting plenty of light in.
2. Do not oversize
A lantern covering roughly a sixth to a quarter of the floor area below usually gives plenty of light. Very large lanterns over small rooms are where overheating complaints usually come from.
3. Let warm air out
Warm air rises and collects in the lantern. An electric opening vent with a rain sensor lets it escape. Opening doors or windows low down at the same time creates a through draught.
4. Shade if needed
Some ranges offer integral or fitted blinds. Internal blinds cut glare, but the heat is already inside the room, so glass and ventilation matter more.
In England, Approved Document O on overheating applies to new homes, not to extensions to existing homes. It is still good practice to apply its thinking to big glazed extensions.
Sources
Written by the Buy Roof Lanterns team. Last reviewed 19 October 2026. General guidance only; your designer, building control body or council confirms what applies to your project.