Tiiveystasoja

Tiiveystasoja is a Finnish term referring to levels or categories of airtightness, i.e., how well a material, component or system prevents air leakage. The concept is used to assess and compare the leak-tight performance of structures, products and assemblies. In building physics, tiiveystasoja describe the airtightness of a building envelope or its elements (walls, roof, windows, doors). Airtightness is typically quantified by standardized tests that measure air leakage under a defined pressure difference; the resulting values may be expressed as a leakage rate (for example, m3/(h·m2) at a specified ΔP) or by related indices such as air changes per hour at 50 Pa in some schemes. Different standards and regulations define different rating schemes, so tiiveystasoja are not a single universal scale but a set of classes or levels used to meet energy efficiency, comfort and moisture control requirements.

In practice, lower tiiveystason (tighter levels) correspond to better energy performance and reduced drafts, but may require proper detailing and ventilation strategy to avoid condensation and indoor air quality problems. The concept is also used in other fields, such as packaging and automotive industries, to describe leakage resistance of containers and assemblies.

The term is common in Finnish technical literature and regulatory documents related to building design, energy efficiency and product testing. It serves as a practical shorthand for comparing and specifying the leak-tight performance of components and systems.