Mold growth modeling of building structures using sensitivity classes of materials

Numerical simulation of mold growth can be used as one of the hygrothermal performance criteria of building structures. Mold growth is one of the first signs of too-high moisture content of materials, and it may affect the indoor air quality and also the appearance of the visible surfaces. Mold growth potential can be predicted by solving a numerical value, mold index, by using the dynamic temperature and relative humidity histories of the subjected material surfaces. The model was originally based on mold growth of wooden materials, but it has now been completed with several other building materials. The model can be used parallel with heat, air, and moisture simulation models or as a post-processing tool. This paper presents the latest findings of mold growth and the modeling of these factors on different materials. The mold growth model has been improved by taking into account the effect of seasonal, long dry or cold periods that do not allow growth. This includes mechanisms for the decrease of mold level (decline of mold index) during unfavorable growth periods and the intensity of the growth after these periods. The laboratory and field results show that the sensitivity of the mold index level may vary in a large range depending on materials. Also, the performance on the interface of two materials has been studied. Instead of modeling the performance separately for each material or product, the materials are presented as different mold sensitivity classes varying from resistant to very sensitive. The sensitive class corresponds to the performance of pine sapwood, which was one basic material in the original model format. Other materials are presented by using the detected correlations between these materials. The mold growth sensitivity classes, decline of the growth level, comparison to detected mold level in materials, and numerical application in practical hygrothermal performance analysis are presented and discussed.