Airtightness and ventilation of a naturally ventilated house in Finland.

This paper illustrates the airtightness and ventilation performance of a recently built ecological house in Helsinki, Finland. The wood frame house, which is built with no plastic vapour retarder, has a satisfactory air tightness (3 ach at 50 Pa). The ventilation measurements show that the outdoor ventilation rate provided by the natural ventilation system tended to be lacking (i.e., less than the required value of 0.5 ach) even though the measured CO2 concentrations were generally satisfactory (i.e., below 1000 ppm) when the bedroom doors were open. Extrapolating the measured ventilation data shows that the ventilation rate is expected to be about 0.45 ach (10% below the required value) in the winter and about 0.25 ach (50% of required value) in the summer when the windows are closed. When the windows are open in the summer, the outdoor ventilation rate will be higher.