Characterising the airtightness of dwellings: Its improvement over time and relationship to construction technique

Purpose: The purpose of this paper is to investigate the distribution of dwelling airtightness test results for a developer, between 2007 and 2011. The changes in airtightness test results over time are discussed, and links between the airtightness test results and the construction technique are investigated. Design/methodology/approach: A data set of airtightness test results was statistically analysed by applying probabilistic model of the distribution and using Bayesian parameter estimation techniques. Findings: The inferred background distributions, those estimated to describe dwelling performance before secondary sealing, suggest an improvement in airtightness between 2008 and 2011, the mode decreases from 5.46±0.09 m3/m2h to 4.12±0.07 m3/m2h with a corresponding shift in practice towards a more target-driven approach. The most airtight dwellings are constructed from reinforced concrete frame, followed by “traditional” (dry lined masonry), timber frame and lightweight steel frame. Research limitations/implications: This study is limited by the size of the available data set (901 dwellings), and by the fact that the data set contains a larger proportion of flats to houses; however, the metadata has enabled the exploration of the link between construction practices and airtightness. Practical implications: Developers need better guidance surrounding how to meet more stringent airtightness requirements through improvements to the primary air barrier, with incentives and support to deliver changes in practice. Furthermore, if a large number of dwellings undergo secondary sealing, this may have implications for the long-term efficiency of the dwelling stock. Originality/value: This analysis investigates two issues that have not previously been studied on a significant number of dwellings: the changes to the distribution of airtightness results over time and the link between construction methods and airtightness.