An innovative test method for evaluating the critical moisture level for mould growth on building materials

The critical moisture level (RHcrit) for mould growth, that is the lowest relative humidity (RH) at which mould can grow, varies between different materials. The factors that most affect mould growth, RH and temperature, also vary in different parts of a building. One way of preventing the growth of mould in buildings is therefore to choose building materials that can withstand the expected conditions, materials that have a higher critical moisture level than the highest expected RH. It is thus crucial that data are available to allow the correct choice of materials to be made. In this paper an innovative laboratory test method for determining the RHcrit of a material is described and discussed. The results from testing of a material according to the method gives information to make the correct choices. The method is developed based on the results of a variety of laboratory studies and has been validated by field studies.