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Condensation on the external surfaces of an insulating glass unit can occur on both the outside or the inside of the building.

The principal cause of condensation on the glass occurring on the internal surface is a high humidity level coupled with a low outside temperature. Areas particularly susceptible to this problem are bathrooms, kitchens and other areas where humidity levels are high. Consideration should be given to improving the heating and ventilation in these areas. Another way to help reduce the problem is to use high performance insulating double glazed units containing an enhanced thermally insulating glass such as the SGG PLANITHERM family. Insulating glass units constructed with low-emissivity (or low-E) energy efficient glass such as SGG PLANITHERM TOTAL actually restrict the heat exchange across the airspace between the two/three panes of glass. This effectively means that the inner pane of glass is kept warmer and so helps to reduce the instances when condensation can form.

Condensated Window

Due to the enhanced thermal insulation properties of a double/triple glazed unit comprising a low-E glass, the outer pane of glass does not get warmed by heat escaping from inside the building through the glass. This results in the outer pane being kept cooler in comparison to a less thermally efficient insulating glass unit. Certain climatic conditions of high humidity levels, without rain, can lead to the formation of condensation on the external surface of the outer pane. It is also possible that due to shelter from nearby trees or buildings, external condensation will appear on some windows but not on others. This phenomenon is due to localised atmospheric conditions and is in no way an indication of a defective unit. Indeed, this can be seen as a positive indication that the enhanced thermally insulating units are actively keeping heat from escaping through the glass.

Extract from document supplied by Saint Gobain Glass UK Ltd.
Weeland Road, Eggborough,
East Riding of Yorkshire
DN14 0FD