Guide
Triple glazing and solar gain: which way do your windows face?
How the g-value works, and when to choose solar-control or high-gain glass.
Triple glazing lets through less of the sun’s heat than double glazing: a g-value of about 0.46 to 0.6 against about 0.6 to 0.72. On north-facing windows that does not matter; on large south-facing windows it can cancel some of the winter benefit while helping keep rooms cooler in summer.
What the g-value means
The g-value is the share of the sun’s energy that passes through the glass into the room, from 0 (none) to 1 (all). The extra pane and coating in triple glazing lower it.
By orientation
- North: little direct sun, so low heat loss matters most. Triple glazing is the clear winner.
- South: useful winter sun. A higher-gain triple unit keeps more of it; in big glazed areas, plan summer shading.
- East and west: low-angle sun in mornings and evenings can overheat rooms in summer; solar-control glass helps.
Your area’s winter sun
The further north you are, the lower the winter sun and the shorter the day. Our local pages show the midday sun height and daylight on the shortest day for each town, which is a rough guide to how much winter solar gain your windows can expect.
Questions
Does triple glazing make rooms too hot?
It tends to keep rooms cooler in summer because it lets in less solar heat. Big south and west windows may still need shading.
Does triple glazing let in less light?
Slightly: light transmission is a little lower than double glazing, typically not noticeable in most rooms.
Sources
More guides
- Is triple glazing worth it?
- Triple vs double glazing: the real differences
- Triple glazing cost guide (October 2026)
- U-values and Window Energy Ratings explained
- Building Regulations for replacement windows: England, Wales, Scotland and Northern Ireland
- Do you need planning permission for new windows?
- Triple glazing and condensation
- Does triple glazing reduce noise?
- Can you put triple glazing in existing frames?
- Triple glazing in period homes and conservation areas
- Trickle vents and ventilation when replacing windows
- Window security: locks, laminated glass and PAS 24
- Windows for Passivhaus and EnerPHit projects
- uPVC vs aluminium vs timber vs alu-clad: choosing a frame
- What happens when your triple glazing is installed
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