Airtightness and ventilation in a mild climate country rehabilitated social housing buildings – What users want and what they get

Abstract Dwellings should be designed for users' wellbeing but frequently their actions seem to contradict the logic adopted in the design. The impact of users' actions and habits on buildings energy efficiency is well established and documented. However, there is a lack of available information concerning the relationship between user behaviour, building airtightness and ventilation. This paper explores the results of a large experimental campaign, which included: airtightness measurements by fan pressurization of flats; continuous CO 2 measurements, and a questionnaire regarding tenants' habits. Forty nine apartments from two different social housing neighbourhoods, one of them recently rehabilitated, were used as case study. Non-rehabilitated flats presented an average ACH 50 of 8.9 h −1 while the rehabilitated flats presented an average of 6.8 h −1 . The impact of user behaviour in airtightness levels was investigated and, in the rehabilitated case study, the average ACH 50 was 4.3 h −1 in modified flats and 7.7 h −1 in non-modified. This can have important consequences on the indoor environment as the average ACH found in a modified flat, ranged from 0.35 h −1 , in December to 1.01 h −1 in August, showing the importance of window opening in the actual ventilation rates. The standard methods for estimating average ventilation rates were applied to the sample and results compared with measurements, indicating a need to adapt currently used methodologies to adequately include user effect. The complexity of human behaviour is a challenge for designers and therefore increasing the knowledge of user actions and habits is decisive for building better homes.