Hydrologic and thermal performance of green, blue and blue-green roofs

Blue-green roofs (BGR) and blue roofs (BR) are emerging technologies, but their performance has not been distinguished from conventional green roofs (GR). This study investigates the hydrologic and thermal performance of six different configurations of extensive BGR, extensive GR and check-dam BR. Using modular setups, the design variables focused on different planting medium types and weep hole sizes. Preliminary results indicate that BGR followed by GR and BR achieved the highest stormwater retention. Substrate type influenced the air temperature above the modules, with organic-based BGR and GR providing the highest cooling compared to mineral-based modules. BR provided less cooling than all BGR and GR modules. Overall, BGR and BR can maximize the urban runoff control and microclimate improvement. However, future implementations should consider the trade-offs between the hydrologic and thermal performance as well as the weight restrictions on roof structures.