The thermal and moisture performance of the wall systems in two unvented residential crawlspace foundations built in Pennsylvania is characterized in this paper. Both wall systems include drainable exterior insulation and concrete block walls with interior insulation in some areas. The results indicate that nonconductive heat loss resulting from air leakage or internal air circulation can affect thermal performance and may greatly increase heat loss. Normalized seasonal heat loss estimated at measurement locations ranged from 1,634 to 5,736 Btu/ft² (18.56 to 65.16 MJ/m²). Absolute humidity was generally higher in the crawlspaces than in outdoor air, and in one of the two homes, the block wall acted as a humidifier throughout the year. Temperature and humidity conditions that could support mold growth were present on crawlspace wall surfaces in both homes for significant time periods, although no mold was observed in either home.