Tiiveystasot

Tiiveystasot is a Finnish term used in building science to describe the airtightness levels of structures, assemblies, and components, i.e., how resistant they are to unintended air leakage. The concept is used to classify and compare how well buildings prevent air from passing through the envelope, with implications for energy use, indoor air quality, and moisture control. In practice, tiiveystasot is most commonly expressed as an air permeability value or as air changes per hour at a reference pressure, most often ACH50, which denotes how many times the indoor air volume would be replaced per hour at a 50 pascal pressure difference.

Measurement and standards: Airtightness is typically assessed with a blower door test, where a calibrated fan creates a controlled pressure difference and measures leakage. Duct leakage tests may accompany the assessment for systems-specific airtightness. International standards such as ISO 9972 (air permeability of buildings) and related European protocols (including EN 13829) define procedures and reporting formats for tiiveystasot. Values are influenced by climate, building type, construction details, and ventilation strategy, and may be reported for the whole building envelope or individual components such as walls, joints, or windows.

Applications and interpretation: Tiiveystasot data are used in energy performance certification, design optimization, and retrofit planning. Lower tiiveystasot generally reduce heat loss and may improve comfort and indoor air quality when accompanied by appropriate ventilation. Typical ranges vary: older or poorly insulated buildings may exhibit higher ACH50, while modern energy-efficient buildings aim for lower values, with high-performance projects sometimes targeting sub-1 ACH50.

See also: airtightness, energy efficiency, blower door test, passive house.