Abstract
Water vapor permeability of building materials is usually measured using dry cup test according to the ISO 12572 standard. For this test, suitable adsorbing desiccant should be used to provide stable low vapor pressure conditions within the cup and, thus, to ensure the good accuracy of the measurement. In this work, different adsorbing desiccants mentioned in the ISO 12572 standard are tested for measurements performed on wood fiber insulation. For each experiment, relative humidity is monitored inside the dry cup. The results indicate that 0 %RH is not reached inside the dry cup and boundary condition is not always stable for highly permeable construction materials, depending on the adsorbing desiccants. The impact of these observation is evaluated on the determination of water vapor diffusion resistance factor and compared to other sources of uncertainties.
Highlights
Water vapor permeability is one of the required properties when performing hygrothermal simulation of building envelopes
A set of dry cup experiments has been performed on wood fiber insulation with a focus on the influence of desiccant
Temperature and relative humidity has been monitored in the air layer between the sample and the desiccant, in the view of evaluating the dryness within the cup
Summary
Water vapor permeability is one of the required properties when performing hygrothermal simulation of building envelopes. This property is mainly determined by means of cup test since the 1950’s. Results obtained in the frame of HAMSTAD project [6] or recently by Janssen et al [5] showed that the highest water diffusion resistance factor for ceramic brick is 4.5 times higher than the lowest one. Possible factors explaining these discrepancies are discussed hereafter
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