Building airtightness is an important parameter to improve the energy efficiency of buildings. By means of a literature study, as well as the use of empirical data on the specific leakage of more than 300 dwellings, this paper provides insights in the relationships between building airtightness and eight individual variables. A total leakage construct was one of the adopted variables to distinguish cases. Correlational analyses, as well as ANOVA tests show that year of construction, total leakage, roof type, construction method and construction typology have significant relationships with building airtightness, but regression analysis suggests that only the year of construction and the total leakage influence the airtightness. Two-way ANOVA tests show that both have a significant interaction on building airtightness, in terms of specific leakage rate. Considering that the year of construction is related to multiple other variables influencing the airtightness of a building and the number of individual leakages and their sizes can only be assessed after completion, both variables cannot yet help us to estimate the specific air leakage of an object in advance.