Quantities used in the analysis of vapour movement through building elements are reviewed. A graphic method of predicting condensation risks is presented, based on the psychrometrie chart: a temperature gradient is constructed by projection to a thermal resistance section of the element, and a vapour pressure gradient by using a vapour resistance section; the latter is converted to a dew-point temperature gradient by parallel projections modulated by the saturation curve of the chart. A worked example is given and the application and limitations of the method are discussed. Some relevant data are included in the appendix.
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