Preventing thermal breakage and associated risk factors


Thermal breakage occurs when the glass pane is exposed to extreme variations in temperature. In these cases, the glass tends to expand and contract. For example, glass will heat under the sun rays and increase its energy consumption. However, if part of the glass pane remains cold, this will unable the glass to expand properly, therefore, creating a contraction that may result in a crack or fracture. Generally, these will appear on the edges of the glass where it’s the coolest, perpendicularly to one side and on both surfaces of the glass. Fractures may be caracterized as monofilament or multifilament.

Usually, the glass is resistent enough to withstand these variations, however, thermal breakage may occur in isolated cases. These fractures are in no way due to a lack of quality in the glass or it’s manufacturing. They may show up, without warning, as much on double pane or triple pane windows. However, there are ways to help in preventing them.


  • When temperatures drop, avoid keeping your blinds or curtains closed. Should you need to keep them closed for a while, ensure that you leave a 40mm gap away from the glass.
  • Direct your heating or ventilating systems toward the interior of the room. Should your systems be parallel to the glass, allow 20 cm in between them.
  • Never paint the glass in part or in whole.
  • Remove any plants or items that could hinder air circulation around the glass.
  • Should your window panes be delivered prior to their installation, store them in a cool dry area, away from sources of heat and sun.

Pertaining to the great outdoors, having a building or a large tree nearby that could cast prolongued shadows on your window, may also create temperature variations. A protective canopy on an outdoor porch could also contribute to thermal breakage. In these cases, following the indoor preventive measures become of the upmost importance.

Moreover, to further prevent thermal breakage, the manufacturer will provide airtight fitting between the panes through glass processing. However, when the temperature gradiant surpasses 30°C between both surfaces, it is recommended to install tempered glass which can resist to soaring temperatures ranging for 100 to 200°C. Nonetheless, this variable depends, among other things, of the glass processing quality around the edges.


  • When the glass pane is in full sun: the variations in temperature are linked directly to the season, the level of sun exposure, its intensity and the angles in which it is exposed. Therefore, windows facing North, in a 45 to 240° angle are less susceptible to thermal breakage.
  • Energetic absorption factor: as the level rises, the more heat is stored within the glass, higher is the risk of breaking. Therefore, energy efficient and reflective glass panes are more susceptible to breaking then clear glass.
  • Frame thermal inertia: as it increases, will hinder the frame from adjusting to outdoor temperatures. The frame must be able to efficiently redistribute the heat from the sun within the surface.

As Canadians, we are confronted to sudden and extreme climate changes. Despite all of the preventive measures, should a thermal breakage incur in your windows, reach out to your nearest Basco specialist to resolve the issue.