Hygrothermal Characterization of Porous Building Materials-New Research Method on Water Vapor Transmission

The research on water vapor transmission (WVT) has an important function on analyzing moisture transport through building materials. According to ASTM Standards, there are two traditional methods (Dry cup and Wet cup) to test WVT of porous materials for practical application, without considering the influence of relative humidity and air flow. In this paper, multilayer method is used to test WVT of porous materials, without the influence of air flow on the whole testing process. Multilayer test method is the new way and there is little experience on how to conduct the whole process, how to obtain the accurate data and make the whole process reasonable is the big issue. Through several cases are worked on and analyzed, then renew desiccant every two hour which is depending on the type of porous materials, is the best way to make the whole testing system reaching to steady state for special building materials. At last, this paper shows that the new way is more reasonable and has higher accuracy than traditional method to get WVT.