Exist’air: airtightness measurement campaign and ventilation evaluation in 117 pre-2005 French dwellings

Between 2017 and 2018, the Centre for Studies and Expertise on Risks, the Environment, Mobility and Planning (Cerema) organized an airtightness measurement campaign in 117 multi-family collective and single-family French dwellings. These dwellings were built before 2005, that is, before the release in 2005 of the fifth French thermal regulation for new dwellings, that was the first to introduce specific requirements for airtightness. The aim of this campaign was to give a clear picture to the French Ministry of Sustainable Development of airtightness and ventilation performance of the existing building stock. To do so, the dwellings were selected to constitute a representative panel that represented the French residential building of the stock. First, a diagnostic protocol was defined to evaluate the state of deterioration of the building, the ventilation performance and the building airtightness. All this information and other details about the dwellings were compiled into a database to be processed. 
Air change rates at 50 Pa (n50) were very variable and ranged from 0.44 hr-1 to 13.7 hr-1.  The results showed that some air leakages paths influenced the airtightness of the panel more than others. Some of them could not be observed before the airtightness measurement and were therefore not easily predictable.  Results also highlighted the fact that some building characteristics were highly correlated to high air change rates. These characteristics were different between collective and single-family dwellings. Unfortunately, the size of the panel (67 houses and 50 apartments), compared with the number of characteristics, did not allow to propose some robust models for airtightness prediction. To address this issue, it was decided to expand the panel with a second airtightness measurement campaign in 2019.  
In the same time, ventilation systems of these dwellings were recorded and their performance were qualitatively assessed without making any measurement. A lack of ventilation was detected in 84% of the houses and 64% of the apartments, either because the system installations were out of date, or because they were too incomplete or if not inexistent.  Yet, when analysing the global air exchange rate, it appeared that it was sufficient in two-thirds of the dwellings, thanks to high air change rate that compensated  the low ventilation performance. The good aeration habits of the inhabitants also limited the risk of condensation on and into the walls and poor indoor air quality.  Those results could be used to update the air change rates used in the French thermal regulation for the rehabilitation of existing buildings, which dated from 2007. In addition, this campaign helped to develop the “A+V+P-“indicator. This is a simple evaluation of the aeration, the ventilation and the airtightness of a dwelling, which could also be promoted by the Ministry to building contractors, as it gives a quick overview of the global air exchange before and after retrofitting.