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What is the difference between single-glazed and thermal insulation windows?

Glazing is the glass part of a window. Windows can have single, double or even triple glazing.

When two panes of glass are assembled and the space in between is filled with argon gas, these are thermal insulation or sealed glass windows.

A standard window has an insulating factor of R2 (R representing the thermal resistance of materials: the higher it is, the better the resistance), while double-glazed insulation windows have an insulating factor of R4.

A triple-glazed insulation window has three panes with the spaces in between filled with argon gas, bringing its insulation factor up to R8. This is why these are usually installed on the north facade of a house, which is the most exposed to the cold. However, because they have more components, they are less transparent than other types of windows and can cause visual and colour distortions.

Thermos double1 EN.png

The double glazing is a minimum to satisfy the standards Energy Star of the South of the province of Quebec and consequently becomes the type of glazing most frequently installed in houses from Quebec.


To make it really more effective, we add a Low-E filter  to improve the window performances by reflecting the heat towards the outside in summer and inward in winter.

Double-glazed vs triple-glazed table

Glazing performance Table.JPG

Source: CAA Quebec

Thermal breakage

Breakage by thermal shock is caused by stresses generated by temperature variations in two areas of a pane of glass. This variation can, for example, develop in glazing that is partly exposed to the sun and partly shaded.

Under the effect of solar radiation, the glazing becomes heated, especially since its energy absorption is high. If a part of the glazing remains cold, it prevents the hot part from dilating freely, thus generating tensile and compressive constraints in the hot and cold parts of the glazing. Since glass is less resistant when dilated than when compressed, the tensile stresses generated are likely to exceed the strength of the glass and cause the glazing to break. This is called thermal stress glass breakage.

This type of breakage occurs at the edge of the glazing, in the coldest area of the frame, and is perpendicular (90°) to the edge and affects both sides of the glass. The fracture can be a single crack or can branch out into a number of separate fissures. (See figure on left)

Risk factors

  • Climatic conditions

  • Glazing characteristics

  • Type (rabbet, bonding, etc.) and quality of glazing installation (shimming)

  • Thermal inertia of the frame

  • The environment outside of the building (neighbouring buildings, trees, etc.) or the building itself

  • The interior environment


With regard to interior environmental factors, risk percentages can be reduced by applying simple measures, such as providing a minimum space (around 40 mm) between the glazing and draperies or blinds, avoiding radiant (radiator, convector, etc.) or forced-air heating directly on the glass, favouring heating that radiates either parallel to the glazing or preferably toward the inside of the room, and ensuring that heat sources are at least 20 cm from the glass.

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