Prediction of mould fungus formation on the surface of and inside building components: Englische Übersetzung der Dissertation, Universität Stuttgart, 2001

The "Third Report on Building Damages" by the Federal Government of Germany in 1996 estimated the costs resulting from mould fungi damages to amount to more than 200 million Euro per year. Different causes, as for example the critical combination of the airtight construction method with insufficient ventilation of the building are given as reasons for the recent increasing occurance of mould fungi in dwellings. Mould fungi do not only occur on the inside surface of external building components, but even inside construction parts. In order to avoid the mould fungus formation in buildings, a strategy has to be set up that focuses on the growth conditions for mould fungi and also considers the complex transient processes of building physics. A prerequisite for preventing mould fungus without the use of biocides is the knowledge of the boundary conditions under which fungus growth takes place. In reference to the boundary conditions for the growth of fungus it turns out that the decisive parameters of influence like temperature, humidity and substrate have to be available over a certain period of time simultaneously in order to enable the formation of mould fungi. The main focus of this paper on hand is to develop a planning instrument from the point of view of an engineer that aims at predicting the formation of mould fungus. A biohygrothermal procedure was developed that makes it possible to predict mould fungus formation and is based on the comparison of the three already mentioned biological prerequisites for the growth of mould fungi and the transient growth conditions occurring in buildings. This procedure consists of two consecutive predictive models, i.e. the Isopleth model and the transient Biohygrothermal model. The Isopleth model makes it possible to determine the germination time of the spores and the mycelium growth on the basis of different isopleth systems that also regard the influence of the substrate for predicting the formation of the mould fungus. The assessment of spore germination on the basis of the Isopleth model has the disadvantage that an interim drying out of the fungi spores cannot be taken into account in case of occurring transient microclimatic boundary conditions. Therefore, a new Biohygrothermal model was developed. This model makes it possible to calculate the moisture balance of a spore in dependence of the transient boundary conditions, thus even to consider interim drying out of the fungus spores. The Biohygrothermal model for predicting the germination of the spores is based on the fundamental idea that a fungus spore has a certain osmotic potential because of the salts, sugar and further substances inherent in the spores. It assumes that humidity absorption first takes place by means of diffusion, until a certain moisture content inside the spore is reached that is needed for starting the metabolism. In order to consider possible influences of the substrate, the Sd values of the spore septum were adjusted in that manner that the spore germination times measured in the Biohygrothermal model correspond with those taken from the isopleth systems in the building material categories. The biohygrothermal process is being validated by observation of plausibility, sensitivity analyses as well as the comparison with the results of laboratory experiments, experiments of outdoor sites, and measurements in occupied dwellings. In all cases great correspondence between the results of the predictive models and the measurements and observations in practice is being observed