Humidity control effect of vapor-permeable walls employing hygroscopic insulation material

Airtight construction and high-performance thermal insulation materials are commonly considered important building features to enhance indoor thermal comfort while reducing thermal load. However, when water vapor is generated in such airtight indoor spaces, it cannot be discharged to the outside, causing interstitial condensation and subsequent intrusion of moisture into the walls. Hygroscopic building materials such as cellulose fiber insulation (CFI), characterized by high water capacity, are a potential countermeasure against such condensation. In this study, the humidity control performance of external walls containing CFI was evaluated using data measured inside a demonstration house and calculated by numerical simulations based on thermodynamic chemical potential theory. The changes in moisture adsorption and desorption were then evaluated for different wall constructions and different climate conditions using a parameter sensitivity analysis. Finally, the effective application of CFI to prevent interstitial condensation was confirmed by comparing different wall compositions.