The Double Glazing Gap - What's In It?

As manufacturers and installers will tell you, there needs to be a gap between the two glass panes in a double glazing assembly. The why is pretty obvious: to reduce heat loss and improve thermal insulation. However, what goes inside the spacer has been the subject of curiosity for some homeowners. What's inside the double glazing gap?

Special Gases in High-End Double Glazing

High-end windows not only make use of expensive materials; they also employ special gases to fill the cavity.

Argon-filled glazing is by far the most common and practical choice in the high-end category. The gas is nonreactive and abundant. Its high density and natural ability to resist air flow make thermal insulation quite effective.

Xenon, krypton and sulfur hexafluoride-filled glazing can do an even better job than argon at thermal insulation. The special gases do a poor job of facilitating heat transfer between the panes, so less heat escapes from the window.

Dry Air in Standard Double Glazing

Meanwhile, conventional double glazed windows and secondary glazing use dry air to fill the gap, hence the colloquial term "air gap."

Air is composite mix of several gases, including oxygen, nitrogen, carbon dioxide, and trace elements of argon, helium and other elements. For air to be considered "dry," the amount of water vapor and humidity must be significantly reduced to 40 percent below the normal figures.

Desiccant

It is essential to keep air dry in double glazing to prevent moisture build-up inside the gap. Maintaining the desired humidity levels is often achieved by preventing outside air from mixing with dry air and by using desiccants to absorb moisture inside the spacer.

During the manufacturing process alone, companies have to make sure that the desiccant does not come into contact with outside air. To allow so would significantly shorten the shelf life of the desiccant and impact its ability to prevent condensation.

There are several types of desiccants that your double glazing supplier could use: common silica gel, calcium oxide, calcium sulfate or molecular sieve (which industry experts say is the best performing variety for technical applications).

Spacer Bar

Finally, the last thing you will notice in the spacer is the bar " an internal framework responsible for maintaining a consistent distance between the two glass sheets. For optimal window performance, choose the warm edge variety.

Unlike the regular bar, warm edge spacers use foam instead of metal. Thus, you can expect better sound-absorption performance to complement the double glazing assembly's insulating properties.

If you want to find out more about the double glazing gap click on the link for an independent guide to the subject.

Sarah Clark is a freelance author who writes for many popular home & garden publications.

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