Interstitial condensation in building structures: Revised model for identifying problem material combinations

The computation of interstitial condensation risk, in particular the rate of condensation, has increased in importance in assessing the acceptability of building details, especially those incorporating insulation or vapour-resisting materials. This Note details a model which incorporates effects currently omitted from the present methods; in particular, the effect of the presence of the saturated water film, the absorption of water by the materials and the latent heat flow resulting from the condensation or drying out process. It is shown that in some simple example cases these effects can considerably alter the conclusions that might be drawn concerning the acceptability or otherwise of a combination of materials and environmental conditions.