Double vs Triple Glazing: Complete UK Cost & Performance Guide

For most existing homes, high-spec double glazing offers the best value. Triple glazing is most worthwhile for new builds, north-facing windows, noise-sensitive locations and homes pursuing high energy performance standards. The UK climate is milder than Scandinavia (where triple glazing is standard), so the energy savings alone rarely justify the cost premium for retrofit projects.

Current Building Regulations (Part L, 2022) require replacement windows in England to achieve a whole-window U-value of 1.4 W/m²K or better. Standard double glazing meets this threshold, while triple glazing exceeds it with values of 0.8-1.0 W/m²K. Scotland requires 1.2 W/m²K, which most quality double glazing also achieves.

A typical three-bedroom house saves approximately £50-£85 per year on heating bills by choosing triple over double glazing, based on current UK gas prices of around 7p/kWh. The saving is higher for larger properties, homes with more north-facing glass, and properties in colder regions of the UK.

External condensation occurs because triple glazing is so thermally efficient that very little heat escapes through the outer pane. On cool mornings, the outer surface stays cold enough for moisture in the air to condense on it. This is a sign of excellent insulation, not a fault. The condensation clears as temperatures rise during the day.

Yes, and this is often the most cost-effective approach. You might specify triple glazing for north-facing rooms, bedrooms (for noise reduction) and large picture windows, while using double glazing for south-facing rooms (to maximise solar heat gain) and smaller windows. This hybrid strategy can save 30-40% compared with triple glazing throughout.

Slightly. Triple glazing has a visible light transmittance of around 65-72% compared with 75-80% for double glazing. The difference is perceptible if you compare panes side by side but is rarely noticeable in everyday use. The additional pane also slightly reduces solar heat gain (g-value of 0.45-0.55 vs 0.55-0.65), which can be beneficial in summer but means slightly less free solar heating in winter.

Modern double glazed sealed units typically last 20-25 years before the gas fill degrades and the seal may fail, causing misting between the panes. Triple glazed units tend to last slightly longer (25-30 years) because the additional pane and seal provide more protection. The frames (uPVC, timber or aluminium) often outlast the glass units and can be reglazed.

Krypton gas is a better insulator than argon (thermal conductivity of 0.009 W/mK vs 0.017 W/mK), but it is significantly more expensive. Krypton allows narrower gas gaps while maintaining performance, which is useful for reducing overall unit thickness. For most residential applications, argon-filled triple glazing provides excellent performance at a reasonable cost.

Yes, triple glazed units require frames with a depth of 80-90mm compared with the standard 70mm for double glazing. Most major window manufacturers offer frame profiles designed specifically for triple glazing. In retrofit projects, the deeper frame may require adjustments to the window reveal, potentially adding £50-£100 per window to installation costs.

Triple glazing has a lower solar heat gain coefficient (g-value) than double glazing, meaning it actually lets less solar heat in during summer. Combined with good ventilation design, triple glazed homes are generally more comfortable in summer, not less. However, ensuring adequate ventilation (trickle vents, opening windows, or MVHR) is essential in any well-insulated home.