Comparative Analysis of Thermal Insulation Performance When Subjected to Various Levels of Moisture

As energy code requirements have become more stringent in the last decade, the incorporation of continuous insulation within opaque assemblies to mitigate the negative impacts of thermal bridging has become the standard for many climate zones. To be installed continuously, the insulation is placed outboard of the air and water barrier in most wall assemblies, which means it will generally be exposed to higher levels of moisture than insulation placed within an interior wall cavity. When the thermal resistance value of insulation materials is determined using standardized laboratory testing, the changes in moisture levels that the material would be exposed to in typical in-service conditions are not accounted for. Because water conducts heat at a faster rate than insulation, the presence of moisture within the assembly could have a negative impact on the thermal performance of the material, and the in situ thermal performance of the insulated wall could be less than the assumed values used for the design of the building. This paper presents an experimental study to evaluate the relative change in thermal performance of two types of insulation when exposed to increasing levels of moisture. A test chamber was constructed that maintains specific temperature and relative humidity levels within the chamber. Insulation was mounted within the chamber, and a series of thermocouple sensors and heat flux sensors was used to monitor the thermal performance of the insulation under steady-state conditions at increasing levels of moisture within the chamber. Keeping the temperature constant, the relative humidity within the test chamber was incrementally increased such that an approximate R-value of the insulation could be calculated at each test condition. The results were compared to determine the effects of moisture levels on the different insulation types that were tested.