Experimental Evaluation of Geosynthetic Vegetation Substrate for Sustainable Green Roof Applications: Thermal Performance and Operational Carbon Mitigation

Green roofs serve as a critical technology for mitigating urban heat island (UHI) effects and reducing building energy consumption. However, conventional green roofs face limitations in large-scale applications due to structural overload from heavy substrate layers. This study proposes a lightweight green roof, utilizing geosynthetic vegetation substrates (GVSs) to overcome structural load limitations. Through a 10-month field experiment in a subtropical climate, the lightweight green roof reduced the roof temperature by up to 29.70 °C, with an average reduction of 15.3 °C, and decreased cooling energy consumption by 22.19 kWh m−2 year−1, corresponding to a reduction of 41% compared with the bare roof. A random forest (RF)-based method has been used to quantify parameter contributions and thereby enabling accurate predictive green roof cooling performance modeling. In addition, a heat transfer mathematical model was developed to calculate roof heat flux and estimate building energy savings. The lightweight green roof achieved an indirect carbon mitigation potential of 12.87 kg CO2 eq m−2 year−1 through energy savings, and a direct carbon mitigation potential of 4.89 kg CO2 eq m−2 year−1 through biomass accumulation. GVS has the potential to balance thermal performance, carbon mitigation and structural constraints on 15° sloped roofs, providing critical technical pathways for carbon neutrality in cities, in line with SDG 11 and SDG 13.