Double-glazing that’s 23% more efficient than triple glazing.

Unless you have changed your windows recently it is more than likely that you will have a 24mm double-glazed unit in your existing frames (uPVC). The majority of window frames in Ireland have what the industry call a 60mm section. In layman’s terms if you measure the window frame from front to back it will be 60mm or thereabouts.

This means that the window frame can accommodate a 24mm double- or triple-glazed unit.

Without getting too technical we will now explain the differences in efficiencies and how Energlaze can make your existing windows 23% more efficient than triple glazing using our new Low-E-Plus2 glass.

To start with we need to know the existing u-values. A u-value is the industry norm for measuring how energy efficient a material is. The lower the u-value the more energy efficient the material is and the more energy you will save. Different materials will have different u-values as you can see in the table below.

Man at window

Material Type



Roof Without Insulation 2.3
  With Insulation 0.4
Cavity Wall Without Insulation 1.6
  With Insulation 0.6
Floor Without Insulation 0.9
  With Insulation 0.6
Solid Wall (block & plaster) 2.3
Cavity Wall (block/polys/block) 0.58
Cavity Wall (timber frame with above) 0.46
Windows, Single Glazing 5.8
Windows, Old Double Glazing (24mm) 2.8
Windows, Triple Glazing (24mm) 1.3
New LOW-E-PLUS2 (24mm) 0.9

We will focus on glass in a 24mm double- and triple-glazed unit.

A standard double-glazed unit comprises 4mm glass, a 16mm cavity and 4mm glass (= 24mm). This type of unit is the most common in Ireland unless the windows have been changed recently. The u-value for this type of unit is 2.8 W/m2K (remember the lower the u-value the better).

If you happen to have a triple-glazed unit in this window frame, then the u-value for this unit will be 2.3 W/m2K, which is an 18% improvement on the double-glazed unit above.

Now this is where it gets interesting.

Recent advances in glass technology by Pilkington’s mean there have been substantial improvements in the thermal efficiencies of glass. We will demonstrate why triple glazing is not as effective as new Low-E-Plus2 double glazing in this case.

If we change the glass in the window frame above (60mm section and a 24mm unit), the new 24mm double-glazed unit will be made up as follows: 4mm Low-E-Plus2, a 16mm cavity filled with argon gas and a 4mm outer pane (= 24mm). The u-value for this unit now becomes 0.9 W/m2K, which is a 70% improvement on the standard double-glazed unit.

If we apply the same to the triple-glazed unit, i.e. two panes of 4mm Low-E glass, argon-filled cavity and a 4mm glass outer (=24mm), the u-value is 1.3 W/m2K,

The triple-glazed unit is now 23% less efficient than the Low-E-Plus2 double-glazed unit from Energlaze with the u-value of 0.9 W/m2K.

This shows that in certain situations the right double-glazing can be more efficient than triple glazing.

The above figures have been calculated using EN Standards 410 + 673/12898.