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With age various plastics and rubbers can shrink

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With age, various plastics and rubbers can shrink, become less flexible and/or permanently deform.Shrinkage can lead to gaps forming at joints. Reduced or inadequate compression can allowincreased air and/or water leakage. The material types and formulations influence the rate at whichthis occurs.3.8Window Thermal BridgingAluminum and glass are poor insulators; they readily conduct cold and warmth. Thermal breaks (nonmetallic elements) are incorporated in modern aluminum frames to help limit this problem. Somesystems have omitted these elements, leading to excessively cold frames and ice accumulation inwinter months.Spacers used at the perimeter of IGUs have historically been metallic. These create a thermal bridgethat conducts cold inwards and causes condensation to form at the glass perimeter.The frame installation is also critical to assure adequate performance.The frame should be alignedwith adjacent wall insulation in a manner to avoid the inner portion being exposed to cold. Insulationalso needs to be provided around the frame to assure continuity of the thermal barrier.However, it is not uncommon for the design to shift the frames too far towards the exterior or placethem in full contact with cold wall elements. This causes the interior frame to become excessivelycold and promote condensation and/or ice.3.9Excessive Solar Heat GainClear glass readily permits solar energy to pass into the building.Where air conditioning is employed,this solar gain represents a major cooling load that the air conditioning system must accommodate.3.10Interior CondensationWindow and door systems have limited ability to resist developing cool interior surfaces during coldweather.Interior air deposits condensation (water) when it comes into contact with a surface that isat a temperature below the “dew point”.As temperatures drop, there is a corresponding reduction inthe interior humidity limit that can be sustained without allowing condensation to form.To control condensation, interior humidity can be controlled by actions that include reducinghumidifying devices and increased operation of exhaust fans.Avoiding elements that obstruct warmair flow, or adjusting mechanical ventilation to direct air onto the problem areas can also providesome relief.
©WSP/Halsall – FOR STUDENT USE ONLYPage F-9Photo 1.: Example of severe condensation from thermal bridging, excessive humidity and poor heatdistribution.3.11Insulating Glass Unit (IGU) Seal FailureInsulating glass units are formed by sealing 2 or more lites of glass together with desiccant exposedto the interior air cavity to maintain low enough humidities that avoid condensation or fogging duringcold weather.These have a limited service life. Even with properly applied and intact seals, water vapour slowlypenetrates the unit and is absorbed by the desiccant.Once the desiccant is consumed, the cavityhumidity rises. Condensation or fogging begins to form in cool weather. The inner glass surfaces

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Term
Fall
Professor
BryanKarney
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