Moisture, Thermal and Ventilation Performance of Tapanila Ecological House

The research presented in this report demonstrates the moisture, thermal and ventilation performance of a recently built ecological house in the Tapanila district of Helsinki, Finland. The single-family house (gross floor area of 237 m2 including the basement and porch) has a well-insulated (250 mm in the walls and 425 mm in the roof) wooden frame with no plastic vapour retarder. A natural ventilation system provides outdoor ventilation and district heating and a wood-burning fireplace provide space heating. The space heating energy consumption was measured to be 76 kWh/(m2*a) of which 29% was provided by wood. For comparison, Finnish houses typically consume 120 kWh/(m2*a) or nearly 60% more energy for space heating. If the building envelope of Tapanila ecological house had been insulated according to the building code, the space heating energy consumption is expected to be 40% higher. The total energy consumption (121 kWh/(m2*a)) and electricity consumption (28 kWh/(m2*a)) were quite low. As a result, the total primary energy consumption was only 162 kWh/(m2*a), while the primary energy consumption in typical Finnish houses is over 40% higher. However, 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 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. The moisture performance of the building envelope was good and the risk of mould growth low. In addition, the moisture transfer between the envelope and indoor air was measured to significantly influence the indoor humidity. At a ventilation rate of 0.5 ach, the results show that a porous building envelope can decrease the maximum humidity in a bedroom during the night by up to 20% RH, which may double the number of occupants satisfied with thermal comfort and perceived air quality. Furthermore, the minimum indoor humidity in the winter can be increased by about 10% RH, which is also important in cold climates. These results show that it is possible to build a house with a porous and vapour permeable envelope that is moisture physically safe and improves the indoor climate.