Abstract
Hygrothermal modelling is increasingly used to inform building envelope design. A key input for these calculations is the material’s vapour diffusion properties. Respecting a growing international concern, this research has questioned the appropriateness of the current test method to establish construction material for vapour diffusion properties. This article reports on the empirical measurement of the vapour diffusion properties of two vapour-permeable building membranes commonly used in Australia residential systems when subjected to variable relative humidity conditions. The method involved completing dry cup and wet cup standard tests as specified in ISO 12572, (23 °C and 50% relative humidity RH). Further tests were then conducted as temperature remained at 23 °C but the relative humidity changed to 35%, 65% and 80%, respectively, in order to know if the diffusion properties are the same or change with varying relative humidity. The results from the wet cup and dry cup tests under different relative humidity conditions were non-linear and different. These results indicate vapour-permeable membranes behave differently when exposed to different relative humidity conditions. In conclusion, this research demonstrates that the current vapour resistivity test method is inadequate, hence the need to establish more detailed diffusion resistivity properties in different humidity ranges that represent conditions experienced within a building’s external envelope.
Highlights
This research has sought to investigate the sufficiency of the current standard testing method for establishing the water vapour diffusion properties of construction materials through laboratory measurement
The aim of this research was to establish if the water vapour diffusion properties of construction materials is variable or fixed, subject to the relative humidity conditions they experience
This line of enquiry has been developed in response to concern about the static nature of the standard test methods to establish water vapour diffusion properties of construction materials
Summary
This research has sought to investigate the sufficiency of the current standard testing method for establishing the water vapour diffusion properties of construction materials through laboratory measurement. The two international standards, ASTM E96m and ISO 12572, have prescribed a single temperature of 23 ◦ C (±1 ◦ C) and a relative humidity 50% (±5%) for conducting the gravimetric water vapour transmission laboratory testing for construction materials [5,6]. These standards have been regularly revised over time, the reality and the demand for modern, healthy and energy efficient homes within our world’s very diverse climates is causing a paradigm shift about the understanding of high-performance building envelope systems’ hygrothermal analysis [7,8,9]. Aside from building durability issues, this will further affect opportunities to reduce carbon emissions generated through the operation of heating and cooling equipment within buildings [18,19]
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