Urban economic development is strongly linked to energy consumption, particularly in cities with the highest energy demand. In semi-arid regions, extensive green roofs (EGRs) have effectively reduced building energy use. This study aimed to assess the potential of EGRs to reduce Heating, Ventilation, and Air Conditioning (HVAC) related peak power demand through a simulation-based approach. We used EnergyPlus modeling software to develop an integrated building energy simulation, evaluating different plant assemblages (Native herbs and grasses, Exotic sedums, Native herbs and exotic sedums, and Native tall grasses and exotic sedums) installed on EGRs under both current and future climate scenarios (SSP3-7.0 and SSP5-8.5) projected for years (2050 and 2080). Our results indicate that during current warm periods, EGRs in semi-arid climates contribute to the passive cooling of indoor spaces, reducing the peak demand for HVAC. However, during cooler periods, EGRs were less effective in maintaining indoor thermal comfort. Assemblages composed of herbaceous plants and sedums exhibited superior thermal performance. Under future summer climate conditions, overall HVAC energy demand is expected to increase, yet EGR treatments showed significantly lower peak demand than traditional roofs. As EGRs deliver multiple ecosystem services in urban environments, they offer a promising nature-based solution with the potential to enhance energy efficiency and mitigate the impacts of climate change.