This International Standard gives simplified calculation methods for: a) The internal surface temperature of a building component or building element below which mould growth is likely, given the internal temperature and relative humidity. The method can also be used to assess the risk of other internal surface condensation problems. b) The assessment of the risk of interstitial condensation due to water vapour diffusion. The method used does not take account of a number of important physical phenomena including: — the variation of material properties with moisture content; — capillary suction and liquid moisture transfer within materials; — air movement from within the building into the component through gaps or within air spaces; — the hygroscopic moisture capacity of materials. Consequently, the method is applicable only where the effects of these phenomena can be considered to be negligible. c) The time taken for water, from any source, in a layer between two high vapour resistance layers to dry out and the risk of interstitial condensation occurring elsewhere in the component during the drying process.