Tiiviystulos

Tiiviystulos is a term used in building physics to describe the measured airtightness of a building envelope, that is, how well the building resists uncontrolled air leakage. It is obtained through an airtightness test, most commonly a blower door test, where a calibrated fan is installed in an exterior door and the building is pressurized and depressurized to a standard pressure difference.

During the test, the airflow required to maintain the pressure difference is recorded. The result is typically reported as Q50, the air leakage rate at 50 pascals, in cubic meters per hour, or as ACH50, the number of air changes per hour at 50 pascals, calculated from Q50 and the building’s volume. Some contexts also report leakage per floor area or provide data normalized for area. A lower tiiviystulos indicates a tighter envelope and lower energy losses, less drafts, and improved indoor comfort. It is a key parameter in energy performance assessments, energy certificates, and compliance with building regulations and green-building standards.

The test is usually performed on completed buildings or during construction when the envelope is sealed, with doors and windows closed and mechanical systems arranged according to standards. Interpreting tiiviystulos requires considering climate, building use, and construction. Values should be compared to applicable national or regional targets for new buildings, renovations, or specialized designs such as passive houses. Limitations include weather conditions, temporary test setup, and the fact that leakage pathways may change over time.