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Moisture permeability measurements under reduced barometric pressures

Galbraith, G.H. and Kelly, D.J. and McLean, R.C. (2004) Moisture permeability measurements under reduced barometric pressures. Materials and Structures, 37 (269). pp. 311-317. ISSN 1359-5997

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Abstract

The successful application of modern hygrothermal simulation models to building envelopes requires accurate values of moisture permeability. Unfortunately, the generation of reliable data is sometimes not possible using the currently-applied gravimetric test methods, because of the extremely long test periods which can be involved. In addition, these test methods are incapable of separating the total mass flow into its vapour and liquid components, the individual transfer coefficients which are required for the complete description of the moisture transmission process. This paper introduces a new approach to permeability measurement, which has been developed to overcome these deficiencies. It involves testing under reduced barometric pressures, which allows a rapid evaluation of permeability, together with the identification of the separate vapour and liquid fluxes. The new approach is validated through the presentation of experimental results for five building materials, which are compared with benchmark data on the same materials obtained from standard tests.