STP1320

    A Logical Extension of the ASTM Standard E96 to Determine the Dependence of Water Vapour Transmission on Relative Humidity

    Published: Jan 1997


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    Abstract

    It is well known that the water vapour transmission properties of hygroscopic building materials depend on the local relative humidities(rh). Traditionally, the ASTM Standard E96 specifies only two conditions of rh. The dry cup method in the standard corresponds to a mean rh of 25 % and the wet cup to 75 %. This information is not enough to describe the behaviour of the material through the entire range of rh. European standards have already proposed an extension of the existing standard to address this issue. ASTM standard should follow this change. A logical extension of the E96 standard to include the effect of rh on water vapour transmission properties has been proposed and is being discussed by one of the C16 Committee Task Groups.

    This paper presents the application of the proposed extension to several common building materials. The details include the operating principles of a constant temperature-rh chamber and the effects on the test results, of the vapour resistance offered by still air inside the cup, the surface resistances and buoyancy. The experimental data were used to critically assess the above effects. The data as well as the analyses of the data are expected to provide guidance to refine the existing ASTM Standard.

    Keywords:

    water vapour transmission, permeability, permeance, relative humidity, building materials, still air, surface resistance, buoyancy


    Author Information:

    Lackey, JC
    Technical Officer, Building Performance Laboratory, Institute for Research in Construction, National Research Council of Canada, Ottawa, Ontario

    Marchand, RG
    Senior Technical Officer, Building Performance Laboratory, Institute for Research in Construction, National Research Council of Canada, Ottawa, Ontario

    Kumaran, MK
    Senior Research Officer, Building Performance Laboratory, Institute for Research in Construction, National Research Council of Canada, Ottawa, Ontario


    Paper ID: STP12292S

    Committee/Subcommittee: C16.33

    DOI: 10.1520/STP12292S


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