Energy performance analysis of extensive green roofs in subtropical regions: A data-driven benchmark for building efficiency

This study evaluates the thermal regulation performance and energy-saving potential of extensive green roof (GR) systems in a subtropical less-developed region. A yearlong field experiment on a nine-story building in Guangxi, China, compared the thermal dynamics of a GR against a conventional roof (CR). Measurements showed the GR significantly attenuated temperature fluctuations, reducing summer peak roof surface and indoor temperatures by up to 8.6 °C and 5.35 °C, respectively. Results indicated exceptional thermal stability, with the GR damping diurnal surface temperature fluctuations by approximately 50%. Furthermore, validated energy simulations across four building typologies reveal that actualized energy benefits are strictly dictated by operational schedules. A substrate thickness benchmark analysis demonstrates that while continuous-operation facilities (e.g., hospitals) benefit monotonically from thicker substrates, intermittently operated buildings suffer from distinct “thermal lag” and “weekend thermal storage” effects, making lightweight configurations dynamically optimal. Ultimately, a practical four-step decision-making flow is proposed to guide urban planners in screening retrofit priorities. These findings elucidate the dynamic thermal buffering mechanisms, providing actionable guidelines for sustainable urban development in subtropical regions.