Double or triple glazing? Low-E, argon, safety and warm edge
The right build-up depends on the opening, the orientation and the actual aim of the project.
More panes of glass do not automatically mean a better solution. We look at thermal insulation, acoustic performance, safety, solar control and compatibility with the window system.
A third pane is not automatically better. It improves Ug — typically from 1.0–1.1 W/m²K for double glazing with Low-E and argon to 0.5–0.7 for triple with two coatings — but the difference in the final Uw is smaller, because the frame counts too. It adds roughly half the weight of a pane, which affects hardware and maximum sash size, and it usually lowers the g value: less free heat in winter, while in Attica the problem is more often controlling the summer sun. For noise a symmetric triple is not better; asymmetric compositions and laminated glass with an acoustic interlayer are.
What goes into an energy-efficient build-up
a Low-E coating,
an argon-filled cavity where appropriate,
laminated or tempered panes according to the requirement,
asymmetric build-ups where particular noise reduction is needed,
a warm edge spacer bar such as Swisspacer or Thermix, instead of a conventional metal spacer.
The warm edge reduces the thermal bridge around the perimeter of the glazing unit, improves the thermal behaviour of the edge and helps lower the risk of surface condensation.
What the third pane actually changes
Thermal insulation. Typical values: double glazing with Low-E and argon around Ug 1.0–1.1 W/m²K, triple with two Low-E coatings around 0.5–0.7. The difference in the final Uw is smaller, because the frame counts too.
Weight. A third pane adds roughly half again to the weight of the unit. That bears on mechanisms, hinges and the maximum sash size.
Solar gain. More coatings usually mean a lower g-value — less free heat in winter. In Attica the requirement is often the opposite: controlling the summer sun.
Acoustics. Symmetric triple glazing is not automatically better. For sound, asymmetric build-ups and laminated glass with an acoustic interlayer are what work.
The spacer at the edge
The linear transmittance Ψg at the glazing perimeter is, to EN ISO 10077-1, in the order of 0.08 W/(m·K) for a metal spacer and about 0.05 for a thermally improved one. In a unit with many small panes the perimeter is long — that is where the difference counts more than in one large glazed area.
Condensation on the outside of triple glazing early in the morning is not a fault: it means the outer surface stays cold because very little heat is escaping.
Frequently asked questions
Is triple glazing always worth it?+
Not automatically. It improves Ug, but the difference in the final Uw is smaller because the frame counts too. It adds weight, which affects hardware and maximum sash size, and it usually lowers solar gains.
Is triple glazing better for noise?+
A symmetric triple unit is not automatically better. For sound, what works is asymmetric compositions and laminated glass with an acoustic interlayer.
Why does triple glazing mist up on the outside early in the morning?+
It is not a fault. It means the outer surface stays cold, because very little heat is being lost to the outside.
