One of the greatest contributing factors to failures of insulating glass (IG) is from moisture and moisture vapor that penetrates the IG edge seals. This can occur from moisture that enters directly into the glazing system and does not exit in a short period of time. Some systems may also have condensation accumulation in the glazing system that becomes trapped, thus allowing moist conditions that can cause moisture vapor to enter into the IG unit more easily. Once the desiccant materials in the unit construction become saturated, the IG unit will exhibit the fogging and water droplets that indicate the presence of a seal that has failed.
Many glazing systems have a weep system incorporated in the framing system to avoid having moisture accumulate around the IG seals for prolonged periods of time. The weep system can consist of holes or slots that will normally drain away any unwanted moisture by gravity to the exterior of the building or to a collection system whereby the moisture is deposited where it will not be harmful to the IG unit or building contents. Look for a weep system usually at the base or horizontal sill of the glazing system. Check to see what the size of the holes or slots are, where they are positioned and whether or not they are properly operating. Some of the telltales as to whether a weep system works is when a stream or water marks show on the building exterior. When the system is malfunctioning or does not work, look for water stains around the glazing system or on the building interior usually around the jambs and sill. Stains can occur at the ceiling and on interior wall finishes that may indicate there is water that is entering the glazing system that passes through as well as stays in the system. It is a sure bet that if some water is passing through some also stays in the glazing channels that contribute to seal failures. One way to check a weep system is to pour water into the glazing channel and observe the weep holes/slots to see if the water exits.
The systems using insulating glass that do not have weep systems need to be examined as well to be certain that moisture does not accumulate that will or is causing seal failures. Some of the same basic inspection methods can be used as referenced in the previous paragraphs to determine if the system is performing adequately or if there may be problems.
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