Window Condensation--Theory into Practice

Thermal performance of fenestration systems often refers to U-factors or solar heat gain coefficients, but condensation inwindows is an even more direct aspect of thermal performance. Sweat on windows does not require expert interpretation: buildingoccupants will quickly and loudly identify acceptable levels of performance without reference to consensus-based standards orbuilding codes.

Many years ago, the author developed a computer model to predict window condensation and this paper describes the useof that model, as well as tools and techniques for in-field assessment and measurement, to either prevent condensation at the designstage or--in some cases--to address condensation-related problems that developed after construction. Specific examples are usedto show how even high-performance window designs can be compromised as a result of poor installation practice--and whatto do about it.