Consideration for the Condensation Resistance of Fenestration Assemblies

The ever stringent focus on the thermal performance of fenestration products for thermal transmittance (U-factor) and solar heat gain (SHGC) ignores the third thermal performance parameter of these systems; condensation resistance. While U-factor and SHGC are areaweighted performance averages of the fenestration system, condensation resistance is a localized condition that relies on performance characteristics of discrete locations in the fenestration system. Performance factors that may have a minimal impact on U-factor and/or SHGC may be critical in the prevention of condensation formation that may, if not controlled, lead to health concerns and building component/system damage. Tighter buildings with reduced fresh air exchanges may exacerbate the problems and concerns with condensation formation on interior fenestration surfaces. This paper compares the differences between the performance of fenestration products relative to U-factor and condensation resistance and outlines principal design features to improve the latter.