This study investigated the feasibility of PCM as a retrofitting option to reduce the zone air temperature and improve occupant thermal comfort under free running condition in an existing house in Melbourne, Australia. Both the experimental and numerical approach were applied in this study. In the experimental study, PCM was installed in the ceiling of one of the rooms and indoor air temperatures of two rooms (one with PCM and the other without PCM) were recorded. A simulation model was developed using building simulation software EnergyPlus and validated using the recorded experimental temperature data. The results showed up to 1.1 degrees C reduction in BED 2 indoor air temperature during daytime and 34% reduction in thermal discomfort hours through the passive installation of PCM on the ceilings. Several simulations including different user behaviour scenario (windows and internal door operations) were carried out to identify the influence of user behaviour on the effectiveness of PCM. It was observed that integration of PCM is more effective in reducing thermal discomfort hours if windows are kept open at night for night purging and the internal doors are remained closed at all time to prohibit any mixing with surrounding zones without PCM. Further improvement in PCM effectiveness was observed when similar amount of PCM was spread in the ceiling and walls. (C) 2016 Elsevier B.V. All rights reserved.