Triple Glazing.
Three panes, two gas-filled cavities and two soft-coat low-E surfaces, in a 36mm (4-12-4-12-4) or 44mm (4-16-4-16-4) build. Centre-pane Ug from 0.5 W/m²K on the krypton-filled spec.
Triple Glazing
Triple Glazed Sealed Units
Standard Unit
36mm (4-12-4-12-4)
Centre-Pane Ug (W/m²K)
From 0.5
Whole-Window Uw (W/m²K)
From 0.8
Acoustic Rw
Up to 44 dB
Sealed Unit Guarantee
15 Year
Install
FENSA Reg 40373
What the third pane actually changes
Triple glazing is not “double, but more”. Adding a third pane changes five things at once: the U-value, the acoustic rating, the weight, the cavity depth, and the economics. Knowing which of those matter on your project is the whole decision.
Thermal. Our standard triple unit is 36mm, built 4-12-4-12-4, with two argon-filled cavities and soft-coat low-E on surfaces 2 and 5. That gives a centre-pane Ug of 0.6–0.7 W/m²K against 1.0–1.2 for modern double. The 44mm build (4-16-4-16-4) with a krypton fill takes it to 0.5–0.6 W/m²K. Whole-window Uw lands at 0.8–0.9 W/m²K on most frames, and 0.76–0.84 on the best-insulated aluminium and composite systems.
Acoustic. Standard triple reaches 36–38 dB Rw against 30–32 dB for standard double. Specify a laminated outer pane and it goes to 42–44 dB. On the A4, A205, A406 or under the Heathrow approach, that difference is genuinely audible.
Comfort and condensation. With 0°C outside, the room-side surface of a triple unit sits at roughly 18°C against 14°C for double. That is what removes the cold-draught feeling near a large window, and what stops the persistent winter condensation and mould you get in north-facing kitchens.
Weight and cavity depth. A triple unit weighs around 30–33 kg/m² against roughly 20–22 kg/m² for double, and needs a 36–44mm glazing pocket. Frames and hinges have to be specified for it from the start — which is why slim period-profile frames often cannot take triple, and why fitting triple into an old frame wastes the money. Solar gain also drops, g-value 0.40–0.55 against 0.50–0.62: a benefit on a west elevation, a penalty on a south one.
For Passivhaus the standard is set on the whole window, not the glass: Uw ≤0.80 W/m²K for new build, ≤0.85 W/m²K for EnerPHit retrofit, with thermal-bridge-free installation. Triple glazing with warm-edge spacers is a prerequisite, but the frame and the install detail decide whether you get there. See Passivhaus windows for the certified frame systems, and double vs triple glazing for the cases where the third pane is not worth paying for.
Specifications
Three panes, two sealed cavities, two soft-coat low-E coatings on surfaces 2 and 5, warm-edge spacer bars throughout. Standard build 36mm (4-12-4-12-4) with argon fill, centre-pane Ug 0.6–0.7 W/m²K. Deep build 44mm (4-16-4-16-4) with krypton fill, centre-pane Ug 0.5–0.6 W/m²K — the make-up used on certified Passivhaus glazing. Whole-window Uw of 0.8–0.9 W/m²K is typical, calculated to BS EN ISO 10077-1; the best-insulated aluminium and timber-aluminium composite frames reach 0.76–0.84 W/m²K. Acoustic performance 36–38 dB Rw standard, 42–44 dB Rw with a laminated outer pane. Unit weight approximately 30–33 kg/m², roughly 50% more than an equivalent double unit, so frames, hinges and lifting gear must be sized for it. Solar gain g-value 0.40–0.55. Room-side glass surface temperature approximately 18°C with 0°C outside.
Two builds. The 36mm argon unit is the standard specification and the right one for most deep-retrofit and new-build work aiming well under Part L. The 44mm krypton unit is the Passivhaus and EnerPHit specification, used where the whole-window target is 0.80 W/m²K or lower. Both are available with a laminated outer pane for acoustics, a laminated inner pane for accessible ground-floor openings, solar-control coating for west-facing and heavily glazed elevations, and obscure or reeded glass for bathrooms. Made to size, including shaped, arched and raked units. Triple glazing must be specified against the frame, not retrofitted into it — a 36–44mm unit will not fit a pocket built for 28mm, and a triple unit in a poorly insulated frame gives back most of the gain. If your frames are staying, double glazing is the honest answer.
Glass Options
Clear is the default and keeps visible light transmission as high as a three-pane unit allows. Tinted covers the solar-control coatings for west-facing and fully glazed elevations, where the lower g-value of triple is being used deliberately. Frosted covers obscure, reeded and sandblasted finishes for bathrooms and overlooked elevations. All three are available in both the 36mm argon and 44mm krypton builds.
