Moisture behavior of polystyrene insulation in below-grade application

•Provide a set of data on moisture behavior of polystyrene insulation in below-grade applications.•Provide comparisons between laboratory and field testing of moisture content by a customized parameter “SVR/Density”.•Provide detail analysis on the criteria set for the selection of thermal insulation in two main buildings codes.•Provide recommendations to better predict the long-term performance for further improvements in the building codes. Expanded polystyrene (EPS) and extruded polystyrene (XPS) are common insulation materials used in thermal insulation systems for below-grade applications. Moisture control components in these systems sometimes fail, resulting in moisture exposure to the surrounding insulation. Although there are several laboratory methods proposed in the literature on the determination of moisture content in polystyrene insulation, the correlations between laboratory data and field data are not evaluated in detail. This paper first conducted an analysis on such correlations and provided a comparison on the laboratory methods defined in different standards. Based on the findings on the correlation study, the criteria on the moisture behavior of polystyrene insulation setting in two main building codes (ASHRAE 90.1 and ASCE 32) that utilize the laboratory data and specific test standards were discussed in detail. Recommendations on the test methods that can better correlate the laboratory data with long-term performance were also present in this paper and these improvements would be able to provide more appropriate information to the building codes.