Field Monitoring of the Hygrothermal Performance of Interior Basement Insulation Systems

Kohta Ueno, University of Waterloo
Aaron Townsend, Building Science Corporation

Keywords

Abstract

An uninsulated basement can contribute a significant fraction of a house’s total heating load: insulating the basement can provide significant energy and cost savings, as well as the potential for more useable space. However, traditional interior basement insulation systems have resulted in a large number of moisture-related failures of the wall system, including significant mold problems. In this research, eight different interior basement insulation systems were installed in a model house in the Chicago, IL area and monitored, including stud walls with fiberglass and polyethylene, rigid foam insulation, rigid foam plus insulated stud walls, rigid fiberglass with a variable permeability facer, and roll fiberglass blanket with perforated facer. In the first year of monitoring, the insulation systems were tested under normal conditions to determine baseline performance. In the second year, a basement water leak was simulated, in the form of a wetting system injecting water into all insulation assemblies. The hygrothermal responses of these walls were compared under both conditions. Due to low humidity interior conditions, none of the tested systems experienced failures. Data showed that the concrete wall and/or exterior soil environment was a source of moisture, even after two years of drying prior to installation of the insulation. This exterior to interior moisture flow highlights the risk of the stud frame/polyethylene assemblies (walls 1 and 2), which place a vapor impermeable layer between the concrete wall and the interior. Some assemblies had very rapid drying rates due to an air leakage path to the interior, but under less favorable operating conditions, moisture issues might result.