In this paper we present a series of leakage tests on extremely airtight dwellings (ACH50 < 0.6 upon completion) in which the durability of the airtightness and the measurement uncertainty involved are assessed. In literature, repeatability and reproducibility issues have been discussed by several authors, along with influences of weather. It remains unclear, however, 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.
In this paper, 4 aspects are studied consecutively: the repeatability and reproducibility of the fan pressurization method in extremely airtight houses, the impact of weather conditions on the measurements, 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 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 values, the additional leaks were modest and the buildings remained very airtight. In general, we conclude 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.