Automated roof segmentation for assessing urban scale energy performance and indoor thermal environment of photovoltaic and green roofs

Urban rooftops have the potential but not-well-explored-yet for adapting to climate change by retrofitting to green roofs (GR) or photovoltaic (PV) roofs. Traditionally, the performance of these two retrofit options on one building roof can only be evaluated separately. This study takes a further step, enabling both energy saving and indoor thermal environment evaluation for mix use of GR and PV together, based on the Urban Building Energy Modelling (UBEM). Specifically, this work proposes a solid automated percentage-based rooftop segmentation approach to allocate GR and PV components and investigate five distinct GR typologies and their interactions with PV installations. Employing detailed building-by-building simulations across 1,236 low-rise domestic structures in Xiamen, China, indicating that (1) A retrofit trade-off exist for balancing the cooling and heating demand reduction, renewable energy generation, and indoor thermal environment. (2) The most effective GR typology reduces cooling demand by approximately 9.06% and heating demand by 7.20% compared to a bare roof. (3) Transitioning from fully GR to fully PV roofs increases renewable electricity generation up to 27.74 kWh/m 2 annually, but also increases cooling and heating demands by 10%, alongside an average annual top-floor temperature increase of 0.20°C. (4) The Pareto trade-off always exists for the retrofit and it is context-specific to the building age and local climatic conditions. Overall, the proposed automated percentage-based rooftop segmentation method based on the UBEM contributes methodological advancements and practical insights essential for urban planning and sustainable rooftop retrofitting. • Assess hybrid green roof-PV systems on 1,236 low-rise buildings. • Achieve 9.1% cooling and 7.2% heating savings with Ajuga Ciliata Bunge roofs. • Increase electricity output by 27.74 kWh/m 2 annually with full PV roofs. • Reveal trade-offs between energy savings and indoor thermal environment via Pareto analysis. • Develop a robust, scalable method for evaluating urban rooftop retrofits.