Thermal performance and energy consumption analysis of eight types of extensive green roofs in subtropical monsoon climate

The green roof is important for sustainable urban development. There is relatively lesser research on the thermal performance of green roofs considering the characteristics of the subtropical climate and differentiated structural design. In this study, the effects of different structural configurations of extensive green roof on its thermal performance under a subtropical monsoon climate condition were explored. The effect of different green roof components (vegetation type, aquifer, soil layer thickness) on energy consumption was investigated. The results demonstrated that (1) the order of cooling ability of three plants was Ophiopogon japonicus > Ajuga ciliata Bunge > Sedum lineare Thunb. (2) Aquifers improved the water retention capacity of green roofs, and higher water content lowered the thermal gradient in the matrix. (3) Among the meteorological factors, the correlation between air temperature and the temperature of each structural layer of the green roof was the greatest, and the correlation coefficient of each layer was 0.871–0.925. (4) Among the three soil thicknesses tested for extensive green roofs, 200 mm was the most energy efficient, which can save 30.2%–56.4% of energy consumption throughout the year. It is concluded that the use of appropriate green roof structures can effectively reduce the roof temperature and save building energy consumption.