To comply with building regulations the industry is required to fit thermally efficient window systems and glass.
External Condensation is a consequence of superior energy efficiency. The high performance coating on the glass reflects heat back into the room. As a result the outer pane of the insulating glass unit remains cooler and presents a colder surface to the outside environment.
The phenomenon occurs in certain climatic conditions, it is even possible that condensation will appear on some windows and not on others. This is due to localised atmospheric situations such as shelter from buildings, trees and even vegetation. Variable wind speeds and air currents will also influence the occurrence of external condensation.
In the Northern European countries where high performing windows are the standard this event is understood and excepted as the householders have become more focused on saving energy and maintaining a comfortable internal environment.
In summary, rather than being seen as a defect of the product, it is a tangible and positive indication that the windows are actively reducing heat loss through the glass.
No matter how clean a pane of glass may appear there may always be contaminates present on the surface. Fingerprints are the most common but any contamination that creates a water –repellent (hydrophobic) layer may produce the formation of distinctive patterns. Grease, glazing materials, suction cups, protection pads and packing materials can also create similar issues. Generally these contaminates will disappear over a period of time with natural weathering and exposure to the elements.
The surface can be cleaned with traditional window cleaning chemicals or a degreasing agent but occasionally deposits can form chemical links with the glass making them more difficult to remove.
In this instance mild abrasives/polishers, such as ‘Jewellers Rouge’ may be required for complete cleanliness.
Again, these variations formed by condensation do not indicate any fault in the glass and has no effect on the performance of the insulating glass unit.
The appearance of the glass should only be assessed under normal viewing conditions as specified by the Glass and Glazing Federation viewing standards.