The Performance project concerns two new buildings erected in 2007 in Paris and near Lyon (France). It has been the opportunity to measure precisely, in a large set of dwellings, the efficiency of the French standard ventilation system (humidity controlled mechanical exhaust ventilation). After an assessment of the performance of the installation (envelop, ductwork and airflows), a total of 30 occupied dwellings has been monitored during two years since November 2007 to measure representative parameters for energy consumption and indoor air quality.