For passive buildings, airtightness is one of primary requirements. Insufficient
airtightness of a building affects a number of related factors. The paper
presents findings resulting from airtightness measurements. Measurements
were carried out using the blower door test. The test revealed defects especially
in the area of window structures. The defects are described in detail, classified
according to their nature and their causes are analysed. Possible solutions to
eliminate all detected defects are proposed. The analysis of the defects shows
that suitable proposals, further improvements of products and technological
procedures can lead to improvements in the airtightness of buildings.