The base of the project is the measurement of air tightness and air change rate in a carefully selected set of buildings in Croatia and in Hungary. Based on the data collected by the application of a shared methodological approach by the common research team, a set of recommendations will be prepared for decision makers, for the industry, for education and for the general public. The results will be shared with the scientific community and published in a text book, applicable in teaching in the future. Achievements: A common way of energy efficient renovation of buildings is by replacing doors and windows with airtight fenestration, however often such an upgrade can lead to problems with air quality in the living space and it can lead to cases of mould. The aim of this joint research project was to examine the air tightness of the diff erent types of existent public buildings in the crossborder region. Fifty buildings from each side of the border were surveyed and categorised according to their structure, age and use, forming the basis for further joint research eff orts in this fi eld.