What the third pane changes
It adds a second cavity and a second low emissivity coating, so less heat escapes. That is real and measurable, and in a cold, exposed, north facing room you can feel it as a warmer surface temperature near the glass.
It also adds weight, roughly half as much again, which is why the frame and hinges have to be rated for it. This is the point where a poorly specified triple glazed window becomes worse than a good double glazed one, because the sash drops and the seal opens.
| Double glazing | Triple glazing | |
|---|---|---|
| From price fitted | £450 | £610 |
| Panes and cavities | 2 panes, 1 cavity | 3 panes, 2 cavities |
| Weight | Baseline | Around 50% more |
| Heat loss | A-rated as standard | Lower again |
| Noise | Depends on glass build | Not automatically better |
| Best case | Most local houses | Exposed or low energy retrofit |
The noise myth
Triple glazing is routinely sold as the answer to traffic noise and it usually is not. Sound reduction comes from mass, from different pane thicknesses and from a laminated acoustic interlayer, not from the number of panes.
An asymmetric double glazed unit with an acoustic laminate outer pane will normally beat a standard symmetrical triple unit on a busy road, and it costs less and weighs less.
A simple decision rule
If your loft and cavity walls are insulated and the room faces north or east with no shelter, triple is a sensible upgrade for that room. If the walls are uninsulated, the same money spent on insulation will do more for comfort than the third pane will.
Room by room is a perfectly legitimate answer, and it is what we quote most often: triple on the exposed elevations, A-rated double with better glass everywhere else.
Get both priced on your openings
We quote double and triple side by side on the same windows so you can decide with real numbers rather than a sales pitch.