Airtightness of single-family houses and apartments has been studied during the past five years in Finland in two large-scale studies by Tampere University of Technology and Helsinki University of Technology. In this paper results from 170 single-family houses and 56 apartments are presented. The mean air change rate of 100 timber-framed houses was 3.9 1/h, 19 log houses 5.9 1/h, 10 AAC block houses 1.5 1/h, 10 LWAC block houses 3.2 1/h, 10 brick houses 2.8 1/h, 10 shuttering concrete block houses 1.6 1/h and 10 concrete element houses 2.6 1/h. The mean air change rate of 56 apartments was 1.5 1/h. It was noticed that with timber-framed single-family houses at least the year the building was built, the method of construction and the material seem to have an influence on the level of air tightness. Masonry and concrete element houses had on average lower air change rate than timber-framed houses and log houses. Fifteen of these houses had a concrete ceiling structure. In these houses, even thought the number of them is relatively small, the airtightness was a bit better than in houses with timber framed ceiling structure. The mean n50-value of log houses was higher than in the other house groups. Log houses with airtight seam insulation material were more airtight than houses with conventional seam insulation material (4.1 1/h vs. 7.9 1/h). Four log houses with additional internal insulation layer had an air change rate of 5.8 1/h. The apartments in concrete element buildings were on average more airtight than apartments in timber-framed multi-storey houses. The n50-values in apartments were in general lower than in single-family houses. In addition to structural solutions, airtightness depends on construction quality. In this study good airtightness, i.e. acceptable according to standards in Scandinavia, was achieved with many different structural solutions