Unlocking rooftop potential for sustainable cities: A systematic review

The utilization of rooftop space offers various benefits to cities and their residents, such as urban heat island mitigation, energy saving, and water management. However, a comprehensive understanding of these benefits and their regional differences is still lacking. We reviewed 97 articles published between 2000 and 2022 to evaluate the efficiency of various rooftop engineering approaches, including green roofs, white roofs, solar roofs, blue roofs, and wind turbine roofs. The main findings are as follows: (I) As of 2020, there are ~245 billion m² of rooftop space worldwide, equivalent to the land area of the UK. About 29%–50% of these rooftops are suitable for utilization. (II) Effective use of rooftop space can cool cities by ~0.60°C, meet ~44% of city energy demand, reduce runoff by ~17%, and save ~23% of building water demand. (III) Climate and building types influence the efficiency of rooftop engineering, with mediterranean climates and low-rise buildings offering the most favorable conditions. This review provides a comprehensive evaluation of global rooftop resources and their potential benefits, offering valuable guidance for cities to adopt differentiated rooftop strategies.