In buildings, favorable growing conditions for mold fungi can occur and cause fungusinfestation. The danger for the occupants of dwellings lies in the spreading of pathogensthrough microorganisms. Mold fungi can occur not only on the surface of external walls, butalso inside construction parts. A prerequisite for preventing mold fungus is the knowledge ofthe transient building physical boundary conditions under which fungus growth takes place.The decisive parameters of influence like temperature, humidity and substrate have to beavailable over a certain period of time simultaneously. Presently common evaluation methodsdo not take into account the transient physical boundary conditions or lack information onmold fungi species and their favorable growing conditions.The problem is uniquely suited for analysis by a numerical simulation model that accounts forcoupled heat, air and moisture transport. A Combined Heat, Air, Moisture and PollutantsSimulation (CHAMPS) model has been supplemented by features to account for the localclimate next to the internal surface of the building parts (micro climate) which is essential forpredicting the formation of mold fungus under realistic climatic conditions. The paperpresents recent advances in CHAMPS modeling as implementation of boundary layerequations for a wall-room coupling and a study on extension to multi-zone simulation.