What is Glazing?

Glazing is the generic term for the transparent, or sometimes translucent material in a window or door. It is the part that you an see through and that lets light pass through. while most common glazing material used in todays windows is glass, other materials such as hard plastic, plastic films and acrylics are also used.

The windows today usually consist of a separately manufactured glazed unit which is sealed to prevent air and moisture from entering the air space. the deal also keeps dirt from getting on the interior surfaces of the glazing. If the seal is broken the only cure is to replace the seal glazed unit.

Some units are make with a single seal and other with a dual seal. the sealant has to perform two functions. One is to hold the glass toothier and the second is to stop the migration of moisture into the unit and gas out of the unit.

Windows are always characterized as being a single, double, or triple glazed which is an reference to the number of panes of glass incorporated into the window. A single glazed window consists of just one pane of glass, a double glazed window consist of two panes of glass separated buy a single spacer, and a triples glazed window contains of three layers of glass separated by two spacers. As a way to achieve the efficiency of a triple glazed window but to avoid the added weight of another full pane of glass, manufacturers will use a transparent plastic film instead of glass as the centre layer.

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Double Glazing | Triple Glazing

Glass itself is not a good insulator, but the air in between the panes of glass does improve the thermal resistance. The width of the air space also influences the insulation value of the window. The optimum air space in a sealed until is 1/2" (13mm). Efficieny is improved with the addition of argon gas. Where smaller spaces are required krypton gas is used. The R-values or the resistance to heat flow at the centre of the glass of the different clear glazing with air space are as follow:

Single Glazing - R1 or U = 1.11
Double Glazing - R2 or U= .49
Triple Glazing - R3 or U = .32


A single glazed window will allow the most light and energy from the sun to pass through. A double glazed window, compared to a single glazed window, reduces solar gain by about 10% for a total of 20% less than a single glazed window. However it is important to understand that the gains in thermal performance offered by a double and triple glazed performance offered by double and triple glazed windows over single glazed windows far outweigh the reduction solar gain.

Window technology such as low-e coating also can reduce solar gain for double glazed windows by 10% to 40% depending on the coating. All windows in Canada should be at least double glazed, (with low-e and gas filled) to achieve the level of energy efficiency and performance required to be effective in our changing climate.