Influence of driving rain and vapour diffusion on the hygrothermal performance of a hygroscopic and permeable building envelope

This study investigates the relative importance of driving rain, plaster capillarity and the presence of a vapour barrier on the moisture content of building materials and the risk of mold growth for a hygroscopic and permeable building envelope (HPBE). Hygrothermal simulations of a single-family house in Denmark mainly made of wood and clay are performed with WUFI. Results indicate that the presence of an overhang is essential to ensure the durability of a HPBE rendered with a capillary active lime-based plaster while the presence of an overhang has a negligible impact for a mineral cement-based plaster. Including a vapour barrier did not introduce significant changes on the moisture content of this wall assembly. Simulation results indicate that the type of plaster and the wind-driven rain exposure are the most critical variables affecting the hygrothermal performance of this wall assembly.