Timber-framed buildings are being studied in Finland in a large-scale study by Tampere University of Technology and Helsinki University of Technology. This paper is based on the measurements of airtightness done in 100 Finnish single-family houses by the fan pressurization method in the years 2002 and 2003.

The mean air change rate at 50 Pa (0.201 in. of water) of the 100 dwellings was 3.9 1/h. It was noticed that the method of construction and the materials used in wall and ceiling assemblies had at least some influence on the level of airtightness. It was also noticed that the airtightness of buildings with a mechanical supply and exhaust ventilation system does not satisfy the recommended level of airtightness in Finland. In addition to structural solutions, airtightness depends on construction quality. In this study, good airtightness was achieved with many different structural solutions.