Biochar in green roofs

Green roofs have captured significant interest as a strategic approach to delivering urban ecosystem services, mitigating the heat island effect, and curtailing building energy consumption; thus, green roofs make a significant contribution towards a sustainable-built environment. Nevertheless, the challenging conditions on rooftops do not favor plant growth. Biochar, a carbon-rich porous material derived from biomass or biogenic waste, stands out as an exceptional additive to green roof substrates owing to its light weight, high water- and nutrient-retention capacities, and inherent resistance to biological degradation. In recent studies, biochar additives in green roof systems have shown effectiveness. This review article aims to guide the research on this topic by outlining the impact of biochar on green roof systems. Biochar-amended green roof substrates enhance water retention, increase plant-available water, curb nutrient runoff, and reduce substrate erosion and density. Particle size and amendment rate are the most influential parameters for the application of biochar to green roofs. However, current biochar use on green roofs has limitations such as a lack of multi-year field studies and the needs for minimizing nutrient losses from soils and optimizing biochar application to a green roof system. Further research recommendations to address these issues are discussed, obtaining more information about how different variables regarding biochar affects overall effectiveness of green roof system by long-term studies. The findings of this study provide a good point of departure to explore the strategies for broader adoption of biochar-based green roofs.