Internal moisture excess of residential buildings in Finland

In Finland, the indoor air conditions of 171 single-family buildings and 49 apartments in multi-family buildings have been studied in large research projects in collaboration with Tampere University of Technology and Helsinki University of Technology. This article deals with the results of moisture excess studied in these single-family buildings and apartments. Continuous field measurements up to 28 months enable to include two consecutive heating seasons in the analysis of the internal moisture excess. The higher 10% critical level during the cold period (T_e ≤ 5°C) was between 3.4 and 4.9 g/ m³ in Finnish heavyweight and lightweight single-family buildings and between 2.4 and 3.6 g/m³ in apartments of multi-family buildings. During the warm period (T_e ≥15°C), the corresponding values were between 0.3 and 2.6 g/m³ for single-family buildings and 0.5 and 1.5 g/m³ for apartments. The number of occupants and the airtightness of different groups of external wall did not have influence on the average values of moisture excess. Slightly better ventilation air change rates were measured in apartments of multi-family buildings, where also the air change rates from supply–exhaust ventilation systems generally fulfilled the Finnish guideline value. The design values of moisture classes in EN ISO 13788:2012 were found difficult to apply for Finnish residential buildings. The upper limit value of humidity class 2 of EN ISO 13788:2012 is suitable for apartments in Finnish multi-family buildings, but too low for Finnish lightweight and heavyweight single-family buildings. Applying the design values of Finnish guidelines would be justified for the studied buildings almost at the full range of outdoor temperatures.