The life cycle research paper retrieval analysis of GRs is depicted in Figure 16, with the node paper analyzed subsequently. GRs typically comprise several components, including the vegetation, substrate, filter layer, drainage material, insulation, root barrier, and waterproofing membranes ^[1][35]. There exist two categories of GRs: intensive and extensive ^[2][9]. GRs proffer a multitude of benefits, such as effective stormwater management ^[3][13], mitigation of the urban heat island effect, enhancement of air and water quality along with improved quality of life ^[4][36], reduction in energy consumption costs for buildings ^[3][13], diminution of noise pollution ^[4][36], and carbon sequestration ^[5][37].

GRs have gained global attention due to their multiple social and environmental benefits and potential to mitigate climate change impacts ^[6][38]. Further research on the life cycle of GRs can enhance their role in addressing climate change and urban flooding. Chenani et al. ^[7][39] performed an analysis of GR layers employing the LCA methodology, culminating in the conclusion that the layers responsible for water retention, drainage, and substrate-encapsulated components with the most pronounced negative environmental impacts. El Bachawati et al. ^[8][40] meticulously examined the Lebanon case utilizing the LCA instrument and discerned that the concrete, rebar, waterproof membrane, and thermal insulation were the primary contributors to potential environmental ramifications. Shafique et al. ^[3][13] and Vacek et al. ^[9][41] conducted comprehensive studies on GRs’ impacts, revealing that construction and disposal stages had higher negative environmental impacts during GR analysis. However, utilizing recycled materials could significantly reduce negative environmental impacts during the material extraction and disposal phases ^[3][13]. Vacek et al. ^[9][41] conducted an in-depth life cycle study on semi-intensive GRs, scrutinizing the effect of incorporating man-made materials on the cumulative environmental impacts of the assemblies. Their findings underscored the necessity for judicious consideration when employing man-made thermal insulation in GRs, given its potential overuse. Nevertheless, man-made substrate replacements, such as hydrophilic mineral wool, can have environmental impacts comparable to those of “natural” substrate mixtures, suggesting that hydrophilic mineral wool could potentially be a more suitable choice than “natural” substrates ^[7][39]. Peng and Jim ^[10][42] embarked on an evaluative study of two types of GRs in Hong Kong—extensive and intensive GRs. They assessed their annual benefits and life-cycle cost-effectiveness under a district-scale installation. The findings indicated that large-scale GR installations can significantly reduce energy consumption, upstream emissions, and atmospheric concentrations. Koroxenidis and Theodosiou ^[11][43], in their analysis of the life cycle of GRs and flat roofs in a Mediterranean climate, concluded that GRs facilitated minor enhancements in energy consumption for heating and cooling (up to 8.30% and 3.50%, respectively). However, they observed substantial reductions in total life cycle energy consumption (8–31%), emissions (24–32%), and waste production (15–60%). This established GRs as a more environmentally amicable alternative to flat roofs, notwithstanding a significant escalation in total life cycle water consumption (279–835%).

The life-cycle environmental performance of GRs demonstrates their potential to contribute positively to urban environments. They can provide significant reductions in energy consumption, emissions, and waste production compared with conventional roofs. However, it is crucial to carefully consider the materials used in GR construction to minimize negative environmental impacts during the material extraction, construction, and disposal stages. The incorporation of recycled materials and alternatives to “natural” substrates, such as hydrophilic mineral wool, can help to further improve the environmental performance of GRs. Additionally, the increased water consumption associated with GRs should be acknowledged and managed to ensure the optimal balance between environmental benefits and resource use. By thoroughly examining the life cycle of GRs, researchers and practitioners can optimize their design and implementation, ultimately enhancing their role in mitigating climate change and addressing urban flooding challenges.

The LCC remains a significant factor in determining the widespread implementation of GRs. A variety of elements, including plant species, waterproofing layers, and lifespan, contribute to the overall cost of GRs. Peri et al. ^[12][44] embarked on data collection from an experimental GR plot to construct a benefit–cost analysis for the life cycle of extensive GR systems within an urban watershed. This comprehensive analysis provided valuable insights into the economic feasibility of GRs across various urban contexts. Yao et al. ^[13][45] analyzed an actual extensive GR situated in Sicily and expanded the examination to include the disposal phase. The study employed eQUEST software (version 3.65) to compare the impact of GRs on building energy consumption. The results revealed that GRs reduced space heating and cooling electricity consumption by 9500 kilowatt-hours annually, or 2.2 kilowatt-hours per square meter, underscoring the long-term economic benefits of GRs implementation. Illankoon et al. ^[14][46] conducted an extensive analysis, calculating the life-cycle costs of over 2000 roofing solution options using the net present value (NPV). The researchers identified optimum solutions for each climate zone in Australia, emphasizing the importance of tailoring GR designs to suit specific regional conditions. The study’s findings indicated that initial and replacement costs played a considerable role in determining the total LCC, highlighting the need for cost-effective strategies in the design and implementation of GRs ^[14][46].

These studies demonstrate the potential for GRs to yield significant economic benefits over their life cycle, particularly when considering energy savings and other long-term advantages. However, further research is needed to explore innovative approaches to reducing initial and replacement costs, thereby making GRs more economically viable for a broader range of applications. By examining the economic performance of GRs through a life-cycle lens, it becomes increasingly evident that these innovative solutions can play a crucial role in promoting sustainable urban development while providing tangible financial benefits for building owners and communities alike.

GRs have been recognized for their capacity to deliver various social benefits, including improved livability, increased urban green spaces, public education opportunities, and enhanced public health ^[15][47]. Despite these advantages, there is a dearth of research examining social benefits from a life cycle perspective.

Bianchini and Hewage ^[16][48] pioneered this area by assessing the NPV per unit of area for both extensive and intensive GRs, incorporating the social–cost benefits accrued over their life cycle. Their analysis revealed that GRs contributed to both personal and societal gains, with a low financial risk associated with installing any GR type. The probabilistic NPV analysis further confirmed the potential for economic advantages for both personal and social sectors ^[16][48]. Expanding upon this, Liu Li-ping et al. ^[17][49] employed an LCA to investigate the private and social costs and benefits of GRs across three region models: metropolises, middle and small cities (MSCs), and new countryside construction farmer model communities (FMCs). The study’s findings illustrated the diverse focus of green roof benefits across these region models. Metropolises prioritized ecological environment benefits, MSCs emphasized social and private economic benefits, and FMCs placed a greater emphasis on private economic benefits ^[17][49]. Further research by Toboso-Chavero et al. ^[18][50] evaluated various growing media (perlite, peat, and coir) for urban rooftop farming using the social LCA method. The research concluded that peat emerged as the most socially amenable growing medium, showcasing superior indicators in impact categories such as community infrastructure, human rights, and labor rights and decent work when juxtaposed with other alternatives ^[18][50].

Collectively, these studies underscore the importance of considering GRs’ life cycle social performances to better understand their comprehensive impacts on communities. By examining the myriad social benefits GRs offer over their life cycle, researchers, policymakers, and urban planners can make more informed decisions regarding the implementation and promotion of these sustainable urban solutions, ultimately contributing to more resilient and equitable communities.