Several studies have demonstrated associations between living in “damp” buildings and health effects such as respiratory symptoms, asthma and allergy. There is only limited knowledge about which agents in indoor air and what levels of exposure that causes the health effects. One possible agent is mould. Because of this there is a strong need for understanding fungal concentrations and physical measurements as they relate to the microenvironment (associations between building characteristics and mould growth). The survey “Prevention of atopy among children in Trondheim” includes both self-reported information about housing, and inspections and measurements from 205 homes. The study includes registered building characteristics such as construction, building materials, installations systems and moisture problems. Measurements include temperature, relative humidity and mould spores in the indoor air. The measurements were made in bedrooms, living rooms, bathrooms, cellars and outdoor air. The data are analysed to detect associations between mould in the houses and the different building characteristics and levels of temperature and relative humidity