Unveiling the design faults of green roofs as novel urban green spaces for enhanced thermal comfort: Lessons from Melbourne

Urban green spaces can enhance human thermal comfort in densely populated cities but creating them at ground level is challenging due to limited land availability. Green roofs offer a promising alternative, and this study examines their effectiveness in providing thermal comfort in summer by focusing on the Sky Park green roof in Melbourne's CBD. Over a month in the summer of 2022, microclimate data from the Sky Park green roof were compared to a nearby paved plaza control site. Surprisingly, the results showed minimal differences in temperature between the two sites, indicating limited thermal comfort benefit from the green roof. The Universal Thermal Climate Index revealed that during opening hours from 8:00 to 18:00, the Sky Park experienced temperatures >32°C (strong heat stress) for 27.8% of recorded hours, compared to 22.3% at the control site. The reduced thermal comfort was attributed to a) the Plexiglas barrier around the Sky Park that hindered ventilation and b) reflective surfaces of nearby buildings that increased radiant heat. The study underscores the impact of adequate site ventilation and surrounding infrastructure on the thermal comfort of urban green spaces on hot summer days and the importance of integrated urban planning to create thermally comfortable environments.