Comprehensive Evaluation of Energy and Environmental Performances of an Extensive Green Roof of a Building in Subtropical Climate

Green roof has been investigated to be one of the effective means for improving the building energy performance and relieving the urban heat island (UHI) effect. This study presents a case study in South China with a subtropical climate to evaluate the benefits of extensive green roof to the building energy, indoor and outdoor thermal environment through field tests and simulations. During the field tests in summer, a room on the top floor of a residential building was covered with green roof as the studied room, and another similar room with conventional roof was regarded as the reference room. The field tests showed that the green roof has better thermal behaviors in terms of heat insulation and thermal resistance capacities. The field measurements and thermal voting tests revealed that better comfort indoor thermal comfort and lower outdoor air temperature above the roof (reduction by 0.9-3°C) can be achieved using the green roof. Based on the results of field measurements and simulation study, 32.7% of the mean daily energy was saved by using the green roof for the room studied, and 0.75% of the total electricity consumption of the city was estimated to be saved if 15% of the buildings in the city are covered with green roofs.