Goals of this thesis are to discover conditions that are suitable for germination of mould spores and design solutions that exclude these conditions. We choose three family straw-bale houses with different constructions. In Area software we calculate flat thermal and moisture fields of details of chosen houses. We compare outcomes of Area software with isopleths system and discover whether there are suitable conditions for germination of mould spores. We discover that the most hazardous areas for germination of spores in straw-bale houses are near wooden elements that are place near exterior in construction. When we place OSB on interior side of wall, we can exclude germination of mould spores in straw-bale house construction.