Single-family buildings and apartments in multi-family apartment buildings have been studied in Finland in two large-scale studies between the years 2002 and 2009. This paper is based on the measurements of airtightness of 170 single-family detached houses and 56 apartments by fan pressurisation method at 50 Pa.The mean air change rate of 10 autoclaved aerated concrete block, 10 shuttering concrete block, 10 concrete element, 10 brick masonry, 10 lightweight aggregate concrete block, 100 timber-framed, and 20 log single-family houses was 1.5 h^-1, 1.6 h^-1, 2.6 h^-1, 2.8 h^-1, 3.2 h^-1, 3.9 h^-1 and 6.0 h^-1, respectively. In concrete-built multi-storey houses, in which the intermediate floor was cast on site, the mean n50-value of 23 apartments was 0.7 h^-1. The mean n50-value of 20 apartments in multi-storey houses built from concrete elements was 1.6 h^-1. 16 apartments in timber-framed multi-storey houses had a mean n50-value 2.9 h^-1.Factors like construction method and insulation material (polyurethane insulation) in timber-framed houses, seam insulation material in log houses and ceiling structure in heavyweight buildings among others were found to have an effect on the average values of air change rates. The mean values of airtightness do not satisfy the recommended level of airtightness in Finland. Most important result, however, is that good airtightness of individual houses was reached within all house groups regardless of the choice of structure, storeys, ventilation system or technology of construction.