Hygrothermal Performance of Exterior Wall Assemblies Under Wind-Driven Rain Across China’s Thermal Zones

Wind-driven rain (WDR) is recognized as a primary source of moisture intrusion in exterior wall assemblies. However, China’s national code for thermal design of wall assemblies predominantly relies on temperature criteria classified by thermal zones, with humidity-related impacts on building thermal performance remaining unconsidered. Thus, the influence of WDR on the hygrothermal performance of exterior wall assemblies necessitates systematic investigation. This study aims to explore variations in moisture resistance among different wall assemblies under WDR exposure and differences in hygrothermal performance of identical assemblies across designated thermal zones. To this end, the hygrothermal behavior of five typical insulated wall assembly types was evaluated across 21 representative cities spanning four major thermal zones in China. Results indicate significant disparities in the hygrothermal performance of wall assemblies under WDR across thermal zones: dryness rates decreased by an average of 100%, 93.33%, 44%, and 30% in Severe Cold, Cold, Hot Summer and Cold Winter, and Hot Summer and Warm Winter Zones, respectively. Furthermore, although certain wall assemblies eventually dried over time, the risk of mold growth persisted. Notably, wall assemblies with external EPS insulation exhibited high sensitivity to WDR, while self-insulated and internal insulation systems were also vulnerable to WDR in the Hot Summer and Warm Winter Zone. In conclusion, annual WDR exposure and U-value are key factors in designing wall assemblies for optimal hygrothermal performance.