GLASS & GLAZING 43
DE-MYSTIFYING CONDENSATION
Will Goodenough of Whitesales discusses the various causes of glass condensation and misting in properties, to help developers avoid the issues.
oth misted glass and condensation are far from uncommon problems. They have plagued homes,buildings and glazings of all sorts for generations, caused by a host of external factors. Although damp is a common problem with single-glazing, modern layered insulated glazing has experienced its own share of condensation, despite the best efforts of manufacturers. This old issue is slightly more complex than people often think. Condensation or window misting implies one significant thing – lack of thermal consistency in a building’s structure. As thermal images demonstrate, many buildings suffer from gaps in their thermal bridges, holes through which energy escapes, causing conflicts of temperature and depositing condensation on the surfaces. These thermal gaps often exist in the form of windows or wall-floor connec- tions. In minor instances, condensation collects and forms damp or just looks ugly. In rare cases, cavities between layers of glazing can gradually fill with water and need replacing entirely. So why does this occur so often, and what can be done to combat it?
B
CAUSES OF CONDENSATION The direct cause of condensation is probably familiar from science lessons at school, where moisture in the air cools and collects on a surface. There are a number of factors however that impact the ways in which moisture forms on surfaces, and where exactly it manifests. Double glazing is particularly prone to condensation, but
CONDENSATION OR WINDOW MISTING IMPLIES ONE SIGNIFICANT THING – LACK OF THERMAL CONSISTENCY IN A BUILDING’S STRUCTURE
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the placement of moisture and on which face it forms can help you to deduce what your particular problem is, and how to deal with it quickly and effectively.
INNER CONDENSATION
Condensation forming on the internal face of the window can usually be put down to one or a combination of several factors: surface temperature of the glass, external temperature and climate, internal air temperature, internal humidity and the
internal ventilation rate. All of these factors (except, of course, the external climate) can be controlled and modified if need be. It is often advisable to try to collect water from the source as soon as possible to avoid condensation and damp problems. Keeping a building well-heated and ventilated will help to prevent condensation, as will warm edge spacer bars, which work to regulate the temperature of the thermal cavity.
OUTER CONDENSATION
At first look it may give the impression of poor glazing, but condensation forming on the outer edge of a window suggests entirely the opposite. Outer condensation is caused by a few external factors: the heat being passed from the interior through the glass (which, itself, is caused by the temperature differences between the inter- nal and external surfaces), heat exchange by convection with the external air and heat loss by radiation. Studies have shown that in overcast weather, heat exchange by radiation is fairly minimal, but in clear conditions a considerable amount of heat is lost to the sky.
The higher the quality of the thermal insulation (measured in U-values), of the
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