The relationship between airtightness and ventilation in new UK dwellings

The UK’s Air Tightness Testing and Measurement Association competent persons scheme collects pressure test data and metadata from the majority of new build dwellings in the UK. This article uses the dataset to investigate the importance of the ventilation strategy in airtightness design and construction. Design and measured airtightness were tested for association with declared ventilation strategy. It was found that ventilation strategy makes a statistically significant difference to airtightness; however, this difference is too small to be practically relevant. Properties with mechanical ventilation and heat recovery (MVHR) were shown to have a mean designed air permeability only 0.46 m3/m2h lower than naturally ventilated dwellings. Seventy-three per cent of homes with MVHR have design airtightness greater than or equal to 5 m3/m2h and 17% of naturally ventilated dwellings have design airtightness less than 5 m3/m2h. We discuss how current design is not maximising the CO2, cost and air quality benefit ...