As shown in the drawing below, triple glazing has a similar construction to double glazing but another pane of glass is added creating two air spaces.
The aim of triple glazing is to provide better thermal and sound insulation than other forms of windows. It is likely that UK building regulations will specify triple glazing as standard on new buildings within 5 years.
The effect of adding another layer of glazing is more glass and components for heat to travel through to escape through the window, therefore a more energy efficient glazing unit.
To maximize the insulating effect the optimum gap required between the panes is about 16mm. Too close together results in radiant heat loss, too far apart leads to creation of gas currents which causes convection current heat losses.
The gap should be filled with inert gas as this provides greater insulation than air due to low thermal conductivity. Argon is commonly used as it is cheap to produce and is about a third better as an insulator than air. Krypton is used in the highest specification units as it has double the insulation property of air. Krypton is however very expensive compared to Argon.
At least the inner, and ideally also the middle pane should have a low emissivity coating. The effect of the coating is to allow short wave length sunlight to enter a room and heat it and to achieve a large reflection on the long wave length sunlight, thus the window minimizes the existing heat loss that exists around all windows.
Low emissivity coating is normally made up of a thin layer of metal which is applied straight onto the glass, or in certain cases onto a plastic film that is attached to the glass. The type of metal used to coat low-emissivity glass will affect the characteristics of the triple glazing.
Most glazed units use glass panes of the same thickness, but this is not a necessary requirement. Most commonly, a triple glazed unit glass specification is 4mm glass on the inner and outer panes and 4mm glass in the middle. Suppliers may also insist on using tempered glass on the middle pane to help the unit to cope with the increased stress on the centre pane that can be caused by deflection.
The panes of glass are separated by spacers. Originally metal spacers were employed, but these were effectively cold bridges and reduced the efficiency of the sealed unit. There was also an increased risk of condensation. Now the spacers are usually made from PVC or PP. Thermoseal Group offers Thermobar warm edge spacer tube (7.5mm - 19.5mm) which is guaranteed to match or better any other UK spacer tube in terms of Thermal performance. It's structural rigidity and symmetry is ideal for triple glazing.
Thermoflex foam spacer system is also suitable for application in triple glazing units