The Honest Answer
Triple glazing improves thermal performance by roughly 20–30% over standard double glazing. Whether that improvement is worth the extra cost depends entirely on your property, your location, and what problem you are trying to solve. We manufacture both double and triple glazed windows, so we have no reason to push one over the other.
Double vs Triple: The Numbers
| Factor | Double Glazed (24mm) | Triple Glazed (36mm) |
|---|---|---|
| U-value (whole window) | 1.2–1.4 W/m²K | 0.8–1.0 W/m²K |
| Glass weight | ~20 kg/m² | ~30 kg/m² |
| Frame depth required | Standard (57mm sash) | Deeper (auto 72mm+ sash) |
| Sound reduction | 32–35 dB | 35–40 dB |
| Cost premium | Baseline | +25–35% |
| Annual energy saving (vs single) | £120–£180 | £150–£220 |
When Triple Glazing Makes Sense
North-facing elevations that receive no direct solar gain benefit most from triple glazing. The same applies to exposed properties in open, windy positions, and to rooms where acoustic insulation is critical — a bedroom facing a main road, for example. If you are building a Passivhaus or targeting an EPC rating of A, triple glazing is typically part of the specification.
When It Probably Doesn’t
South-facing windows already benefit from solar gain in winter, which offsets heat loss through the glass. Adding a third pane reduces that solar gain while adding weight, cost, and frame depth. For most London period properties, the 20–30% improvement in U-value translates to an energy saving of roughly £30–£50 per year over double glazing — meaning the payback period on the triple glazing premium can exceed 25 years.
Weight and Sash Operation
Triple glazed units are approximately 50% heavier than double glazed equivalents. For sash windows, this means heavier counterweights, stronger cords or chains, and a deeper sash rail to accommodate the thicker unit. Our triple glazed sash windows use an automatic 172mm frame depth to handle the additional weight safely. The sash still operates smoothly, but the proportions are subtly different from a traditional single-glazed window.
Our Recommendation
For most London homes, high-specification double glazing with Low-E coatings, argon fill, and warm-edge spacers delivers the best balance of performance, aesthetics, and value. We recommend triple glazing selectively — on north-facing or noise-exposed elevations — rather than whole-house. Use our 3D configurator to compare double and triple glazed options side by side and see exact pricing for your window sizes.
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