ISO 13788:2001

Hygrothermal performance of building components and building elements -- Internal surface temperature to avoid critical surface humidity and interstitial condensation -- Calculation methods

This standard gives calculation methods for:

• 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 surface condensation problems.
• The assessment of the risk of interstitial condensation due to water vapour diffusion. The method used assumes built-in water has dried out and does not take account of a number of important physical phenomena including:

• the dependence of thermal conductivity on moisture content;
• the release and absorption of latent heat;
• the variation of material properties with moisture content;
• capillary suction and liquid moisture transfer within materials;
• air movement through cracks or within air spaces;
• the hygroscopic moisture capacity of materials.

Consequently the method is applicable only to structures where these effects are negligible.