Green roof as a passive cooling technique for the Mediterranean climate: An experimental study

Urban areas are undergoing increasing growth and land consumption. The built environment can contribute, by means of sustainable design and strategies, to mitigate the pressure on urban systems. To this aim, passive strategies can be integrated into buildings to improve their performance and that of the entire urban infrastructure system. Green roofs are among the most encouraged passive strategies, which can be added to both new and existing buildings. Green roofs reduce Urban Heat Island effect, keeping the building and the city cooler; contribute to the stormwater management system, reducing runoff-flooding risk. However, while these advantages have been studied extensively, the actual cooling potential from evapotranspiration of green roofs has not been the subject of many studies. In this work, the passive cooling potential of green roofs by evaporation by means of preliminary experimental studies on two green roofs is investigated. In greater detail, we aim at disentangling the peculiar role of the substrate layer, without vegetation, during both a simulated extreme rainfall event and normal irrigation regime, and we compare it to the performance of a gravel-composed reference roof, whose performance with respect to cooling is already good. Results demonstrated that the green roof without vegetation is able to cool down the roof, and the intense rainfall event was the one that provided the highest thermal performance to the roof.