What thickness of glazing should you choose for your windows?

glazing should you choose for your windows

The thermal comfort within your home depends on several factors. However, it is often said that a lot of heat is lost through and around windows. This is why in this section, Quelle Energie explains how to choose the thickness of its double glazing to optimize its insulation, and, consequently, reduce its heating bill.

The installation of insulating windows makes it possible to sustainably reduce the energy expenditure of the dwelling. Calculate the heating savings you can achieve by installing this system.


Before talking about thickness, we must already make the distinction between single, double and triple glazing. Single glazing consists of a single sheet of glass , 4 to 6 mm thick for the most common models. With a thermal transmission coefficient Ug close to 6 W/K.m², it is the least insulating glazing . Note that the higher the value of Ug, the less efficient the glazing.

Double glazing has better thermal performance . It is made up of 3 layers whose thickness varies and arranged as follows: two glass blades are separated by an air blade. Air is a very good insulator and its insertion in the middle of the glass allows much better insulation than with a simple glass pane. The most common models are rated 4/12/4 and 4/16/4, that is to say 4mm of glass on either side of 12 or 16mm of air. The total thickness of the double glazing is therefore generally 20 or 24mm. However, there are thicker models with a 20mm air space and full 28mm thick glazing. They are not necessarily more effective for insulation because convection movements can be created in the layer of air which are detrimental to the overall performance of the glazing. Double glazing makes it possible to reduce the thermal transmission coefficient Ug to a value close to 2.8 W/K.m², it is therefore twice as efficient as single glazing. Replacing air with Argon gas even makes it possible to reach a value of 1.2 W/K.m². The addition of a layer of metal oxides on one of the interior faces of the double glazing further enhances thermal performance with a Ug coefficient of 1 W/K.m².

The characteristic thicknesses are as follows: 32mm for the 4/10/4/10/4 glazing and 36mm for the 4/12/4/12/4 . The triple glazing provides very good insulation with a Ug value of 0.7 W/K.m². However, it has drawbacks such as poorer light transmission and a solar factor (which characterizes solar gain and therefore free heat) lower than that of double glazing. Due to its thickness, it is also heavier than double glazing and therefore requires well-adapted joinery.

Windows are once again eligible for the tax credit at a reduced rate of 15% (capped at €670 per equipment) in replacement of single glazing. In addition, care must be taken to respect certain values ​​of the Ug coefficient for the glazing or Uw for the complete window as well as a minimum solar transmittance factor Sw. The following table summarizes the target values:

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