Triple glazing is the headline premium upgrade over double glazing. Three panes instead of two, two argon-filled cavities instead of one, better thermal performance — it sounds like an obvious win.
In the Nordic and German markets, triple glazing is now standard on new homes. In the UK, it's typically a 20-30% price uplift over double glazing. The question is whether the extra cost pays back in the real world of UK domestic retrofit.
The honest answer is more nuanced than most window salespeople admit. Here are the numbers.
| Metric | Modern A+ double glazing | Triple glazing |
|---|---|---|
| Number of panes | 2 | 3 |
| Cavity fills | 1 argon-filled | 2 argon-filled |
| Centre-pane U-value | 1.0 W/m²K | 0.6 W/m²K |
| Whole-window U-value | 1.2-1.3 W/m²K | 0.7-0.8 W/m²K |
| Weight per m² | ~20 kg | ~30 kg |
| Unit depth | 28mm standard | 44mm minimum |
| WER rating | A+ | A++ |
| Acoustic reduction | ~32 dB | ~38 dB |
| Price uplift over double | baseline | +20-30% |
A U-value of 1.2 W/m²K means: per square metre of window, per 1°C temperature difference between inside and outside, 1.2 watts of heat is lost per second.
For a typical 3-bed UK semi with around 18 m² of window area, and an average UK winter indoor-outdoor temperature difference of 10°C over the heating season (6 months):
Annual heat loss through windows: ~1,130 kWh per year for the whole house.
At current UK gas price (~7p per kWh delivered heat, accounting for boiler efficiency): £79 per year in heating cost attributable to window heat loss.
Annual heat loss through windows: ~660 kWh per year.
Cost at same gas rate: £46 per year.
£33 per year. At a typical whole-house triple glazing uplift of £1,500-£3,000 over the double-glazing equivalent, the payback period is 45-90 years.
This is the number the industry doesn't shout about. For most UK domestic retrofit scenarios, triple glazing does not pay back on energy savings alone within the lifetime of the windows themselves.
Those payback numbers are for a typical UK retrofit. There are real scenarios where triple glazing is the right choice:
If you're building to Passivhaus or AECB Silver Standard, triple glazing isn't optional — it's required to hit the overall U-value targets for the building envelope. In these projects the windows are just one component of a holistic airtight, super-insulated design where every element pulls its weight.
With very large windows (say, 10m² of south-facing glazing in a living area), the difference in surface temperature between double and triple glazing on a cold night is meaningful — roughly 2-3°C warmer inner pane with triple. This reduces radiant chill near the window, the "cold-room" feeling you get sitting by a large window on a January evening.
Worth the uplift on principal living spaces with large glazing, not on every window.
If you live on a flight path, next to a railway, or on a busy A-road, the extra 6 dB of acoustic reduction from triple glazing is noticeable. 6 dB corresponds roughly to halving the perceived loudness.
For most suburban locations, double glazing + curtain is already sufficient. For genuine noise nuisance locations, dedicated acoustic double glazing (with laminated inner pane) often outperforms standard triple glazing and at lower cost. See our glass and glazing guide for the options.
The payback calculation above assumes an average UK climate. In the Scottish Highlands, Cumbria, or Yorkshire Dales at altitude, the annual heating demand is higher and the payback shortens — possibly to 20-30 years on an all-triple retrofit. Still long, but more defensible.
The payback calculation uses today's ~7p/kWh gas price. If gas prices double in real terms over the next 15 years (not implausible), the payback halves. If you're planning to stay in the home for 30+ years, the long-term case for triple is stronger than the short-term pure-payback arithmetic suggests.
A few practical considerations that the marketing material tends to downplay:
Triple-glazed sealed units weigh roughly 50% more than double. This means beefier hinges, higher-rated multi-point locks, and more wear on the opening mechanism over 20+ years. Sash drop (where the latch edge of an opening sash gradually sags below the frame latch) happens sooner on triple.
Modern A+ double glazing sits in a 70mm frame (our Rehau Total 70 is exactly this). Triple glazing needs an 80mm or thicker frame minimum, typically 85-90mm. You lose roughly 15mm of glass area per sash to the thicker frame, which can be visible on narrow openings.
Counterintuitively, triple glazing causes more external condensation on cold mornings than double. Because less heat passes through the unit to the outer pane, the outer pane stays colder and collects dew. This is a sign the window is working well, but it can look alarming and some customers hate it.
Triple-glazed units are made in smaller volumes than double. Expect 3-5 weeks lead time from most UK fabricators vs 10-14 working days for double.
We supply high-quality A+ rated double glazing (Rehau Total 70 with 28mm argon-filled sealed unit, low-E inner pane) as our standard specification. It's the right answer for the vast majority of UK domestic retrofit customers.
We don't offer triple glazing in our online range because the configurator price calculations for triple would be misleadingly expensive for customers who actually need A+ double. If you have a specific Passivhaus, deep-retrofit, large-glazed or serious-acoustic project that genuinely needs triple, call us on 0800 861 1450 — we can custom-quote via our UK manufacturing partner.
The golden rule: buy the best double glazing you can afford rather than the cheapest triple glazing. A well-specified A+ double (Rehau Total 70 + argon + low-E + warm-edge spacer) outperforms a budget triple with poor spacer bars and cheaper profile.
Our Rehau Total 70 double glazing delivers 1.2-1.3 W/m²K, well ahead of Part L minimum. Instant online pricing.
Open the Configurator →Back to Blog • Related: Glass & Glazing Guide • Rehau Total 70 profile