For promoting energy-efficient building design, various green building certification schemes such as BREEAM, LEED, DGNB, Green Mark, BEAM Plus, ASHRAE Standard 90.1, Code of Practice for OTTV, etc. have been developed around the world. In recent years, photovoltaic system is widely adopted in building application. This system can offer double benefits: (i) generating electricity by absorbing and transforming solar energy; (ii) reducing heat gain transmitted into a building through building envelope. Since the current building certification schemes were originally developed for buildings constructed with conventional building materials, the reduction in heat gain resulted from the application of photovoltaic systems cannot be properly reflected in these building certification schemes. This study investigates the effect of photovoltaic systems on the thermal performance of buildings. Three existing buildings located in subtropical Hong Kong were used as case study. It was found that the effect of photovoltaic glazing system on the reduction in heat gain was significant (ranging from -13.59% to -38.78%). Based on the findings from this study, it is recommended to incorporate the effect of photovoltaic glazing system into the OTTV regulation in Hong Kong. The methodology developed in this study can be applied to other building certification schemes and energy codes.