Water Vapour Permeance Under Isothermal and Non-Isothermal Conditions

Abstract

This report describes the effect of temperature gradient on the water vapour transmission properties of building materials. The generated temperature gradient across a test material is validated with thermal analysis by using SOLIDWORKS (3D CAD software). The water vapour transmission measurement technique used for this study is a modified cup method, which has constant 50% mean relative humidity. The two wall sheathing membranes, asphalt saturated kraft building paper and Polymer based sheathing membrane were tested under isothermal and non-isothermal boundary conditions. The comparison was made between the results of isothermal and non-isothermal boundary conditions. The results obtained from non-isothermal test conditions show increase in water vapour transmission rate (WVT) and water vapour permeance of asphalt saturated kraft building paper. On the other hand, the results of polymer based sheathing membrane show decrease in WVT rate and not much significant change in water vapour permeance.