Traditional building technologies establishing highly-breathing multi-layered wall systems provide healthy indoor environment and energy efficiency in buildings due to the use of lightweight, porous, water vapour permeable and thermal resistive building materials. The breathing performance of traditional buildings and materials that contribute to the healthy indoor conditions and air quality are needed to be investigated in detail. That knowledge on breathing performance has also vital importance for the improvement of the contemporary building and materials technologies. The study was conducted on three kinds of porous masonry units: mud brick, collected from the sound parts of the traditional houses of Hamzalı Village, Kırıkkale (Turkey) and autoclaved aerated concrete (AAC) type G2 and type G4, the commonly used lightweight concrete material which are also produced in Kırıkkale. These three groups of materials were examined in terms of their air exchange properties by means of laboratory analyses. Some supportive laboratory analyses were also done on material characterization of the samples. The experimental setup is developed for the analyses of the samples, particularly for the assessment of air flow through the material by using CO2 as tracer gas. The interpretation of the results were done in order to compare the porous building materials in terms of their effects on indoor air quality. The double-zone experimental setup based on concentration decay procedure was found to be useful to better-understand the air exchange features of a material in terms of rates of concentration decrease and increase in neighbouring zones by monitoring the concentration of outgoing air. The data achieved is expected to improve the contemporary building walls by benefitting from the self-ventilation capability of building materials and to provide healthier indoor conditions for the occupants. The results are also useful to discuss the airtightness aspect of passive house technology and to minimize the mechanical ventilation needs for fresh air intake by benefitting from the self-ventilation performance of air permeable skin.