Durability and Measurement Uncertainty of Airtightness in Extremely Airtight Dwellings

Abstract In this paper a series of leakage tests is presented on extremely airtight dwellings, studying the durability of the airtightness level and the measurement uncertainty involved. All houses subjected to testing are certificated passive houses, meaning the maximum air leakage rate upon completion was n50 < 0.6 h-1 air changes per hour at 50 Pa pressure difference. In the literature, repeatability and reproducibility issues have been discussed by several authors, along with influences of weather conditions. However, it remains unclear to what extent the available uncertainty intervals are relative or absolute. With the current tendency towards extremely low leakage levels and the introduction of airtightness requirements in building codes, the further exploration of this issue has become crucial. Four aspects concerning air leakage tests are examined: the repeatability and reproducibility of the fan pressurization results in extremely airtight houses, the impact of weather conditions on the measurement results, the impact of the age of the construction, and the reproducibility of the airtightness level in repeated construction of virtually identical houses. The latter is limited to short term effects since all dwellings (n = 15) were completed after 2010. The results show similar relative repeatability and reproducibility intervals to those found in the literature. The rather large effects of weather conditions reported in previous studies could not be reproduced. Normal wear and tear due to occupation of the dwelling proved to introduce substantial relative deterioration of the airtightness of the building shell (20–100% increase in leakage), although in absolute value, the additional leakage was modest and the buildings remained very airtight. In general, it is concluded that pressurization tests render robust results in extremely tight construction, but with respect to ambitious leakage limits, test conditions and small preparation details such as the locking of window hardware can easily determine whether the dwelling will pass or fail.