Activities of moulds from domestic dwellings are normally classified into three groupsprimary, secondary, and tertiary colonizersaccording to the minimum relative humidity they require to colonize a substrate. With the help of isothermal calorimetry it is possible to directly measure the thermal activity from moulds as a function of climatic parameters. This makes it possible to provide more precise and detailed information of the growth behavior of these types of moulds under different temperature and relative humidity level than traditional methods. From this study, it is found that the optimal relative humidities and the recovery from drying are different for these three different colonizers. The fungal activities during desorption process are higher than during adsorption processes under the same relative humidity level for all of the samples. Such information makes it possible to model mould behavior indoors and can be used to access the risk for mould growth in the buildings.