Indoor air quality (IAQ) is one of the most important factors for the welfare of the society. Indoor air quality is a complex result of different simultaneous affecting factors. Numerical and experimental simulation studies about the moisture transfer between structures and indoor and outdoor air spaces are relatively well known, but the transfer of volatile organic compounds (VOCs), particles and microbes from or through the building envelope to indoor air have been studied insufficiently. A new laboratory device, the IAQ simulator chamber, has been designed and constructed to study the effect of building materials and structures on the IAQ. The IAQ simulator device can be used to study structure components between controlled ‘indoor’ and ‘outdoor’ air spaces, which brings new perspective to the research when compared to the applicability of conventional emission test chambers. The test structure or the outdoor air may contain materials having biological growth that are impurity sources for air. The effect of these sources on the indoor air can be studied under different heat, humidity and air pressure difference conditions. The measurements include evaluation of moisture content of materials, humidity, temperature, air leakage through the building structure, air pressure difference, analyses of indoor air quality (Volatile organic compounds VOC, particles and microbes). This paper presents a short study, where Microbial VOC and new molecular biological techniques were applied to detect and quantify microbes on building materials and in air samples using small conventional emission chambers and the IAQ simulator device. The IAQ simulator device offers a new tool to study the complicated causal connections of building structures, materials and unexpected exposure to water and microbes, especially during the use of the buildings. The results can be used together with a whole building hygrothermal analysis to give ideas to a risk assessment of the building performance under realistic climatic loads. Also renovation concepts needed to protect the indoor air from emissions of polluted building materials can be studied.