Comfort

How Roof Window Blinds Help With Summer Glare and Heat

Roof windows are brilliant for daylight and awkward in a heatwave. This guide sets out honestly what an internal blind changes, what it does not, and how to get the most from it.

Why roof windows gain heat and glare

A roof window is angled towards the sky, so through the middle of the day it receives sunlight closer to head-on than a vertical window does. That means more direct light entering the room, and more of the sun's energy arriving with it.

Attic rooms also sit at the top of the house, where warm air collects, which is why they are usually the first rooms to feel uncomfortable.

What an internal blind can and cannot do

An internal blind is very effective against glare: it puts an opaque or diffusing layer between the sun and your eyes, so screens become readable and the room stops feeling harsh.

On heat, the honest position is more limited. By the time sunlight has passed through the glass, much of its energy is already inside the room, so an internal blind manages the room rather than stopping the gain at source. It helps, but it is not a cooling system, and we do not publish any temperature or percentage figure for it.

Blackout versus light-filtering in summer

Blackout fabric is the stronger option against direct sun because it is opaque, and it is what most people close in the middle of a hot afternoon. Light-filtering fabric keeps the room usable and bright while taking the edge off the glare, which suits a working day.

Some households fit blackout in the bedrooms and light-filtering in the rooms used during the day for exactly this reason.

Internal versus external shading

Shading fitted on the outside of the window intercepts sunlight before it reaches the glass, so it addresses solar gain earlier than any internal product can. Internal blinds are easier to fit, cheaper and control glare and privacy from inside the room.

Appropriately designed shading is recognised as an established measure for reducing overheating risk in the SEAI guidance document Overheating risk in new dwellings. That guidance models dwelling design rather than testing any individual internal blind, and nothing in it should be read as a performance figure for this product.

A practical daily routine

Close the blind before the room heats up rather than after — mid-morning on a south or west-facing window. Open windows in the cooler part of the evening to let the warm air out, and raise the blind again once the sun is off the glass so you get the daylight back.

Small habits like these make more difference than any single product choice.

Common questions

Will a roof window blind cool the room down?

An internal blind shades the room and can reduce glare, but it manages heat rather than removing it: much of the sun's energy is already inside once the light has passed the glass. We do not publish any temperature or percentage figure.

Is blackout or light-filtering better against summer sun?

Blackout is the stronger option against direct sun because the fabric is opaque. Light-filtering keeps the room bright and usable while cutting glare, which suits rooms used during the working day.

Is external shading better than an internal blind?

External shading intercepts sunlight before it reaches the glass, so it addresses solar gain earlier. Internal blinds are easier to fit and control glare and privacy from inside the room.

When should I close the blind on a hot day?

Before the room heats up rather than after — typically mid-morning on a south or west-facing window — then open up again in the cooler part of the evening.

Primary sources

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VELUX® is a registered trademark of VKR Holding A/S. Bizzy Blinds is an independent supplier of aftermarket blinds compatible with VELUX roof windows and is not affiliated with VELUX.