Moisture permeability data presented as a mathematical function applicable to heat and moisture transport models

The physics of moisture transfer is complex and as a result modelling is normally carried out on a macroscopic basis, with empirical coefficients used to simulate the transport process. These coefficients are not single values but depend on the moisture content of the material. The application of this data within the simulation environment requires the determination of a systematic methodology for its presentation. This paper investigates the transport coefficient referred to as the vapour (or moisture) permeability. This coefficient is central to the accurate simulation of moisture transport. A detailed analysis of various functional relationships between vapour (or moisture) permeability and relative humidity is carried out and a possible form of equation proposed. An initial data-base of material moisture permeability data is then reported for a range of common building materials.