Moisture damages and failures in buildings are caused by hygrothermal conditions exceeding the tolerance of structures. In building materials these conditions may lead to the growth of microbes or mould and decay fungi after a critical exposure time. The microclimate is the acting force for biological deterioration of materials. Microclimate condition is a result of several simultaneous vectors: macroclimate (rainfall, temperature, humidity, air pressure conditions etc.), meso-climate (location of the building, building structures and details and the materials used). During the service life of a building, several factors may cause aging of building and materials. Failure to perform as intended can be of various degree: excess moisture can cause reversible or irreversible deterioration or performance degradation resulting from biological processes, chemical processes or physical changes. The critical factors affecting durability and service life should be considered and taken into account during the planning and building process as well during the use and maintenance. In this paper, modelling of mould growth and decay development based on humidity, temperature, exposure time and material is presented as a tool for the moisture risk analyse and evaluation of life time of different building materials and structures. The occurrence of decay means a severe risk for the structure performance. Mould growth may affect the indoor climate, but this depends strongly on the site for the growth. Mould on exterior surface of the structure or in material layers inside the structure enclosure cause less risk for indoor air than those adjacent or close to the indoor air space. Other risk factors are, for example, the reason for moisture increase (accidental or continuous), area for high level moisture content, species of mould, etc. The risk assessment and criteria of the moisture induced growth of organisms presented in this paper are essential in order to be able to analyse the needed and suitable renovation methods. Limited moisture levels and low microbial activity with no significant contact to indoor air may require only some follow up. On the other hand, overestimation of the actual risk may cause massive structural renovations that cost too much compared to the methods that are adjusted according to the risk.