Guide
Triple vs double glazing: the real differences
U-values, solar gain, weight, noise, condensation and price, side by side.
Triple glazing has three panes and two cavities; double glazing has two panes and one. A good triple unit loses about half as much heat through the glass (Ug about 0.6 against 1.1 W/m²K), is about 50% heavier, lets in less solar heat, and costs about 20 to 30% more. For noise, a laminated acoustic pane matters more than the third pane.
Side by side
| Measure | Good double glazing | Triple glazing |
|---|---|---|
| Panes and cavities | 2 panes, 1 cavity (e.g. 4-20-4) | 3 panes, 2 cavities (e.g. 4-16-4-16-4) |
| Centre-pane U-value (Ug) | About 1.1 W/m²K | About 0.6 W/m²K (two low-e panes); 0.5 with wider cavities |
| Whole-window U-value (Uw) | About 1.2 to 1.4 | About 0.8 to 1.0 |
| Solar gain (g-value) | About 0.6 to 0.72 | About 0.46 to 0.6 |
| Glass weight (4 mm panes) | About 20 kg/m² | About 30 kg/m² |
| Sound reduction (Rw) | About 29 dB (4/16/4) | About 3 dB better; more with laminated panes |
| Typical price | Baseline | About 20 to 30% more |
Heat loss
The U-value measures heat flow through one square metre for each degree of temperature difference. Halving the glass U-value roughly halves heat loss through the glass. Frames, spacers and installation matter too, which is why the whole-window figure is the one to compare.
A thin triple unit can be worse than double
BRE points out that a thin 28 mm triple unit with only one low-e coating has a centre-pane U-value of about 1.2, no better than a good double unit. Triple glazing only performs when the cavities are wide enough and two panes are low-e coated. Ask for the unit build-up and the whole-window U-value on any quote.
Solar gain
The third pane and extra coating block some of the sun’s heat. On a north-facing window that does not matter much. On a big south-facing window, the lost solar gain can cancel part of the benefit in winter, and help in summer. See our guide to solar gain and orientation.
Weight and frames
Triple units are about half as heavy again, so frames, hinges and rollers must be rated for them. That is why triple glazing usually means new frames, not new glass in old ones.
Noise
The third pane adds only a few decibels. If noise is the reason, choose an acoustic laminated pane and mixed pane thicknesses, in either double or triple. See acoustic triple glazing.
Questions
Is triple glazing twice as good as double?
At the centre of the glass, a good triple unit loses about half the heat of a good double unit. Across the whole window the gain is smaller, typically from about 1.2 to 1.4 down to about 0.8 to 1.0.
Is A++ double glazing as good as triple?
Energy ratings include solar gain, so an A++ double window can rate as well as a triple one. On heat loss alone, triple glazing is lower.
Sources
- BRE: is triple glazing better than double?
- Glass Technology Services: triple glazing weight and performance
- Pressglass: sound insulation of glazed units
More guides
- Is triple glazing worth it?
- 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
- Triple glazing and solar gain: which way do your windows face?
- What happens when your triple glazing is installed
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