Double glazing conserves heat

Press, 8 June 1989, Page 35

Double glazing conserves heat

The modern home, which uses windows as architectural features as much as for light and ventilation, has large areas of glass which, apart from preventing wind and rain from penetrating, has no insulation value at all. This means that the warmth generated inside will pass straight through and be lost.

With the ever-increas-ing price of electricity, coal and oil, it becomes more and more important to curb that waste. Consequently, double glazing is becoming a far more sensible and financially viable method in limiting energy loss as well as condensation and noise.

There are many forms of double glazing. For example, if one is not too fussy about being able to see through the window or what friends may say, then a sheet of clear plastic, stapled or taped

to the inside of a sash, would be the cheapest form of double glazing. Moving one rung up the ladder, it is also possible to glue or secure with beads, another pane of glass behind the existing one. This, unfortunately, generally results in condensation forming between the two panes which progressively gets worse until visibility is lost forever.

There are commercial secondary double glazing systems, which consist of a new aluminium window fitted behind the existing one. This is made up of sliding panes so that access to the existing window can be gained by opening the inside one.

This system, however, has been slowly losing favour to more modern methods which blend far better with the window structure and are generally less expensive. The old secondary win-

dow, though useful in its day, meant having to open the first window so that the second could be opened. This of course introduced dust, grime and insects into the cavity which were difficult to get to. The amount of glass area to be cleaned was doubled and the system meant that blinds and curtains needed to be reinstalled out from the wall. The fact that a complex aluminium extrusion was involved pushed prices high, quite apart from modifications and new soft furnishings. The double glazing now offered at Canterbury Glass is quite different, as sealed insulating glass units are available.

These units have virtually all of the characteristics of ordinary glazing as they are hardly noticeable in a window and require no more

maintenance than normal glass. The success of the sealed double glazing unit can be attributed to the trapped air cavity which is sealed against moisture permeance and the peripheral spacer which contains a drying agent. The combination of these factors prevents condensation forming on the inside of the unit. Compounds formulated expressly for the manufacture of sealed insulating units, having an extremely high resistance to moisture vapour, are used for the seal. The seal is extruded wet, under controlled factory conditions, into the rebate formed by the aluminium spacer. The glass must be absolutely clean and free from dust before this process, as once the seal has been applied the air cavity between the panes is quite inaccessible.