Abstract
Today, there are many variations in water vapor control membranes including smart vapor retarders (SVRs), that function as vapor barriers but whose water vapor resistance drops when the ambient relative humidity becomes high. In the first half of this study, the change in water vapor resistance against ambient relative humidity in both directions was measured using the wet-cup method for the four types of two-layer SVRs consisting of hydrophobic and hydrophilic membranes and one type of vapor retarder. All the SVRs showed high water vapor resistance under an ambient relative humidity of 60% or less and low resistance above 75%. Additionally, a clear directional dependence of the water vapor resistance was observed for all SVRs. In the latter half of the study, two sets of small-scale field tests were conducted for six types of membranes, including polyethylene foil, under hot and humid summer weather conditions in Japan. The relative humidity dependence and water vapor diffusion direction dependence indicated by the cup method were validated and confirmed. In addition, the water vapor resistance in the ambient relative humidity range of 70–75% obtained by the cup method was strongly related to the retention of dryness of the specimens in the field tests.
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