A prospective Study on the Evolution of Airtightness in 41 low energy Dwellings

Airtightness of the building envelope is an important parameter affecting the performance of (low energy) buildings. In case the airtightness is effectively measured, this is typically only done once as part of the commissioning of the construction work. Several factors could affect the evolution of the airtightness of the envelope after the building is constructed. In this work, follow-up airtightness tests have been carried out to investigate the evolution of the performance in the interval of 0.5 up to 12 years compared to the original pressurisation test. The results on 41 low-energy dwellings indicate that the airtightness is indeed not a fixed value over time. Of the 41 buildings, 29 display an increased air permeability resulting in an increase of up to 200% in relative terms or up to 1.36 ACH50 (air changes per hour at 50 Pa pressure difference [h-1]). Conversely, four of the buildings in the dataset show a significant improvement of the airtightness; resulting in a decrease of air leakage of up to -1.19 ACH50. Analysis of the data shows that on average the air permeability at 50 Pa pressure difference increased by 38%, but with great variation depending multiple factors such as initial airtightness value and construction type. This corresponds to an average increase of the specific air permeability of the building envelope of 0.15 m³/(h·m²). Most of the buildings under analysis are low energy buildings or passive houses which were very airtight at time of construction. Despite the observed evolution in air permeability, many buildings under investigation can still be considered sufficiently airtight a few years after initial construction