Double glazing, triple glazing or super-insulating glazing – which should you choose?

In a poorly insulated home, almost 40 % of the heat loss occurs through the windows. So it is crucial to choose the right glazing.

Super-insulating glazing or high-efficiency glazing is now replacing conventional double glazing. Its insulation capacity is two or three times greater, thanks to a layer of gas between the two panes of glass and a film of iron oxide.

Triple glazing is also available. This is even more efficient, but is far more expensive and is therefore often too great an investment compared with the energy savings it brings.

The lower the U value, the better the insulation

To compare the different types of glazing, you need to take into account the U value. This indicates the quantity of heat that passes through the glazing. This U value is expressed in watts per square metre and Kelvin (W/m²K).

U value comparison for different types of glazing

	U value	Temperature of indoor surface*
Single glazing	5.8	-1.8°C
Double glazing	2.8	9.5°C
Super-insulating glazing	11	15.9°C
Triple glazing	0.6	18°C

* _{at an outdoor temperature of -10°C and an indoor temperature of 20°C}

U value comparison for various forms of glazing and frames

Glazing is not enough to guarantee insulation. The frame also plays an important role. For instance, a window fitted with triple glazing that does not shut properly will not be very efficient.

Comparison of U insulating values depending on the type of frame and glazing:

Glazing Frame	Wood	PVC one room	PVC several rooms	Aluminium without thermal break	Aluminium with thermal break
Single glazing	4.8	5.1	4.7	5.9	5.4
Double glazing	2.8	3	2.7	3.7	3.2
Super-insulating glazing	1.8	2	1.7	2.6	2.2
Triple glazing	1.5	1.8	1.4	2.3	1.9

Price

As for the price, this depends on the fitter and on the type of frame chosen, as well as the available energy grants.

However, also keep the following in mind:

single glazing is no longer used at all
double glazing and super-insulating double glazing cost virtually the same
on average, triple glazing is around 60 to 80 % more expensive than double glazing. In addition, triple glazing can only be fitted into high-quality PVC or (more costly) aluminium window frames. Moreover, the hinges need to be reinforced so they are able to take the weight.

Triple vs.double glazing

Ultimately, a lot of construction industry professionals believe that triple glazing is not worth the extra outlay and is advisable only in exceptional cases. Those who champion the cause of passive house construction, on the other hand, consider triple glazing indispensable…

Super insulating double glazing is less expensive and in itself already offers high grade thermal comfort.

Moreover, glass foil-covered double glazing also ensures excellent acoustic comfort.

Wood: most recommended

Wood is naturally an excellent insulator, and is therefore the material most recommended. As far as possible, opt for FSC labelled rather than chemically treated wood.

Aluminium:easy maintenance & long-lasting

Aluminium is also an interesting option, provided it is used with thermal breaks (an insulating element added to the frame to limit energy loss), particularly given its easy maintenance and long useful life.

PVC: environmentally harmful

PVC provides acceptable performances but is relatively harmful to the environment and requires a great deal of maintenance.