Humidity is the essential condition for biological growth on facades. Beneath wetting by driving rain, condensation occurs in consequence of long wave radiation in clear nights by reaching temperatures below the dew point of the air. The importance of this wetting mechanism is obvious with regard to the occurrence of microorganisms mostly on the northern sides of buildings. In this paper results of field examinations of two construction types (ETICS and high insulating monolithic constructions) will be evaluated concerning to time periods in which the surface temperature falls below dew point temperature. In order to do a comparison between different construction types and thermal transmittances hygrothermal calculations will be done. For this, a new model which includes long wave radiation effects, is used. The influence of the thickness of the insulation (respectively thermal transmittance), and also the orientation of the construction will be shown exemplarily.
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