Airtightness retrofit and construction practices, unintended consequences, and ventilation practices: Gathering evidence to improve airtightness in the UK housing stock

Airtightness retrofit and construction practices influence airtightness, but more research is needed to quantify the effect of a range of airtightness measures across a range of dwellings.Most unintended consequences of more airtight dwellings are ameliorated with sufficient ventilation. Fire risk is an exception to this rule, and is poorly researched.Ventilation practices are driven by several stimuli and differ based on the type of ventilation in place, be that natural or mechanical. There is no evidence to suggest that a practically relevant difference in airtightness exists in new dwellings based on ventilation type.Research purposeThe first aim of this research is to understand the construction practices related to airtightness: the effect of airtightness improvements, airtightness failure points, ways to address airtightness failure points, the relationship between airtightness and build quality, and the influence of PAS 2035:2023 and PAS 2030:2023 in driving higher airtightness standards.The second aim of this research is to understand the unintended consequences of more airtight dwellings in the UK.The third aim is to understand how and why occupants ventilate their homes, to know if they do so sufficiently and appropriately, and if they have the knowledge to do so efficiently.Research methodologyThree Rapid Evidence Assessments were carried out. The first Rapid Evidence Assessment, which screened 1,497 documents for quality and relevance, and subsequently reviewed 26, reviewed research on airtightness construction practices and risks that relate to airtightness in the UK housing stock. The second Rapid Evidence Assessment screened 75 documents and reviewed 36 on the risks and unintended consequences of more airtight dwellings. The third Rapid Evidence Assessment screened 266 documents and reviewed 40 on ventilation practices.Analysis of secondary data from the Retrofit Revisit project investigated the durability of airtightness over time. Analysis of over 5,000 airtightness tests from existing GB dwellings investigated the presence of clustering around compliance thresholds to detect in-test temporary sealing.Construction practices, unintended consequences, and ventilation practices© Crown copyright 2025