A System of Permeability Specification for Use in Moisture Simulation Models

Abstract

The successful application of moisture simulation models to building enve lopes requires accurate values of material permeability. Unfortunately, al though the presently available database is reasonably voluminous, much of the information contained therein is of limited use in such applications. This paper describes the specification of permeability data in terms of the differ ential permeability function. Several alternative mathematical forms are com pared using experimental results from a representative range of building mate rials and the most appropriate form is identified. The use of this function allows the accurate evaluation of permeability appropriate to the humidity conditions to which a material is subjected in practice. On the basis of theoret ical analysis, it is also suggested that this function allows the separation of the total moisture flux into its vapour and liquid components. This hypothesis has been tested for two materials using a prototype experimental procedure in which permeability measurements are made under different barometric pres sures.

Keywords

Permeability Moisture Condensation Building materials Dampness

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