This article proposes to study the impact of envelope and internal partition walls airleakage distributions, on the indoor air quality (IAQ) performance. It is based on a preliminary performance-based approach using formaldehyde with three emission levels (low, medium, high). This multizone modelling (CONTAM) approach uses as performance indicators, the average concentration per room as well as the percentage of time of exceeding the limit value (ELV) of 9 µg.m-3. This work allowed to highlight that the ELV was largely exceeded for the high and medium emission scenarios, whether for balanced ventilation or exhaust-only ventilation, complying with the regulatory flow rates. And this, respectively in 100% and 90% of the time for balanced ventilation, and 100% for exhaust-only ventilation. Impacts on concentrations of detailed external and internal airleakage distributions are higher with exhaust-only ventilation than with balanced ventilation (52% and 18% of maximal variation between the different distributions, respectively).