Life on earth would not be conceivable without fungi, bacteria and other microorganisms. These organisms are responsible for the fast decomposition of dead material, splitting it up into its components and thereby giving it a new access to a further life cycle. Therefore microorganisms as fungi and bacteria are important components of our ecosystem. In buildings, however, favourable growing conditions for mould fungi can also occur and cause fungus infestation. Despite the quality of house building having improved over the last decades, especially by measures aiming at the reduction of heat losses due to transmission and ventilation, the number of reports on building damages caused by microorganisms, especially by mould fungi is still increasing. 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. Whereas before the energy crisis in the 1970's regulating the temperature was mainly operated by opening the windows, today, because of energy saving reasons, airing is not done as frequently. Especially the unintentional ventilation due to leakages was reduced considerably. As a result the air humidity in rooms rises. Thereby mould fungi do not only occur on the inside surface of external building comp onents, but even inside construction parts.

The danger for the occupants of dwellings lies in the settling and spreading of pathogens (disease causing agents) through microorganisms. Therefore, consequent measures have to be taken to avoid health dangers that come from mould fungi on the surface of building components. For example, when selling a building in the USA proof has to be furnished guaranteeing that the dwelling is free of the mould fungus Stachybotrys atra. In comparison to health aspects, building damages caused by mould fungi - i.e. the 16 destructive effect the fungi have on building materials, like bio-corrosion or bio-fouling - only is of minor importance. For that reason the scientific paper on hand does not deal with building damages nor with legal problems ever occurring in this conte xt.

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. The application of biocides is always accompanied by additional health risks, especially when used indoors, and moreover can prevent the formation of mould fungus only over a limited period of time. Moreover, biocides often have a very selective effect, so that other fungi or microorganisms can spread instead. Besides a considerable limitation for the selection of biocides is to be expected within latest EU directives. 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 ormation of mould fungi. The presently common valuation methods for the growth of mould fungi do not, or only indirectly, take into account the transient boundary conditions. Whereas in German publications mainly the relative humidity is given as only criterion for mould fungus formation, the relative humidity in dependence on the temperature is seen as a cause by international experts. These characteristics usually do not allow any greater differentiation regarding the influence of the substrate, i.e. of the building material or the degree of contamination. Therefore, the main focus of this scientific 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. This instrument is provided for being used by building physicists or consulting offices acting in the field of the building sector. This is also the reason for the deliberately chosen

17 simple approach employed in this interdisciplinary scientific paper. 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 isopleth system describes the hygrothermal prerequisites for the growth of the fungus. It consists of a boundary line that is dependent on the temperature and on the relative humidity regarding fungus activity, and of isolines that indicate spore germination time when spore germination is to be predicted, and stand for growth per time unit when the description of the mycelium growth is co ncerned.

Significant differences exist among the various fungus species. Therefore, when developing common isopleth systems only fungi were regarded that are dangerous to human health and also can be detected in buildings. Quantitative statements on the growth conditions temperature and humidity will be set up for these more than 150 species that fulfil both features, as far as they are given in literature. To further clarify the differentiation of the life phases of the mould fungi, the data for spore germination and mycelium growth will be given separately. In order to differentiate the mould fungi according to the health dangers they may cause, the so called hazardous clas ses will be defined as follows: ...

• fungi: growth and growth model

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