External Condensation on UPVC Windows

External Condensation on a UPVC Window

External condensation on UPVC windows is a natural phenomenon caused by the outer pane of the glazing being colder than the glass that it replaced. With single glazing and older style double glazing windows a larger proportion of heat was lost to the outside through the glass. Current legislation to meet energy efficiency in homes and to protect the environment, now requires newly fitted glass units to prevent as much heat loss through the glazing area as possible. Therefore all modern glass products fitted must achieve this standard irrespective of the company that fits them.

This in-turn means the outer pane is not heated as much, the result of this being external condensation can form on the outside windows at certain times of the year. Usually external condensation might be noticed during the first few weeks of Autumn or the first few weeks of Spring.

It is also possible that external condensation will only appear on some windows, but not others. This is due to localised atmospheric conditions such as shelter from nearby trees or buildings along with variable currents and wind speed.

There is not much that can be done to avoid the risk of condensation to the outside. Heating the room more would have an effect but this understandably is not an ideal option. In many cases the external condensation does not last long, a little heat from the sun warms the outer glass enough to evaporate the moisture or a gentle breeze will clear the external condensation up.

Gardinia’s Climat Gard XL double glazed units are more energy efficient thanks to a high performance Low-E transparent coating that reflects heat back in to the room, allowing significantly more heat to be kept inside.

Please note that external condensation on high performance Climat Gard XL double glazed units is in no way an indication of a defective unit. This can be seen as a positive indication that the units are actively reducing heat loss through the glass.

Think of this as a similar phenomenon as to why some houses on a street have a lot of snow settled on the roof when it snows, then other houses have none. The houses with snow on the roof have a highly insulated loft which is not allowing heat to escape and melt the snow. In comparison the houses with no snow on the roof do not have very good loft insulation, meaning a lot of heat is been lost through the roof, which is melting the snow.

More can be read about external condensation on the Saint Gobain Glass Website and on the Pilkington Glass Technical FAQ.