The relationship between airtightness and summertime infiltration rates

All new dwellings in England and Wales are required to undergo a model-based overheating risk assessment prior to construction. An important model input is the building infiltration rate, which is usually estimated using a conversion factor on the dwelling airtightness. There is a paucity of evidence regarding the reliability of these methods in summertime. This aim of this paper is to provide new evidence on the relationship between airtightness and infiltration during summertime. The airtightness of a single test house was repeatedly measured over a three-month period using a blower door. Following this, 15 whole house tracer gas tests were undertaken in the same test house over a summer season to measure infiltration rate. Eleven different infiltration estimation methods were used to calculate the infiltration rate and were compared to the measured infiltration rate. The summertime infiltration rates were predicted to be between 64 and 208% higher than measured. These findings have implications for the reliability of overheating risk assessment and suggest that these uncertainties must be accounted for when designing and modelling buildings to be resilient to summertime overheating.