Evaluation of Multifunctional Aspects of a Green Roof in Mitigating the Negative Effects of Urbanization in Mediterranean Environment

Green roofs have a potential to mitigate the negative effects of urbanization and represent a viable solution for increasing stormwater retention while improving the energy performance of both new and existing buildings. They are still a pivotal point against the more and more complex climate change, increasing urban biodiversity and replacing the vegetated footprint that was destroyed when the buildings were constructed. This study aims to analyse a technological installation of a green cover on a flat terrace, applying temperature sensors and a rainwater recovery system. For this purpose, two green roof prototypes were installed that differ each other exclusively for the vegetation planted (all plants suitable for the Mediterranean climate, but with green or grey leaves). At the base of each one, the stratigraphy varied for the presence or absence of XPS panel. Substrate, the same for both prototypes, was made up of lapillus, pumice and compost (20% -65% -15%). Monitoring was performed using three data loggers for measuring the external temperature and that recorded under each type of substrate. The simultaneous installation of a weather station allowed to check temperature, wind, humidity and rainy events in the site. The results obtained in the first months of experimentation show the effectiveness of the roof in containing temperatures. Data from data loggers show that the green roof was able to keep the underlying environment cooler by about 2°C during the thermal peak and warmer by the same amount at the minimum external temperatures, with variability due to substrate humidity and to colour of plant cover. The rainfall measurements, until now scientifically insufficient for the scarce rain amounts, will be implemented for existing roofing and evaluated as well as the benefits that the use of green roofs entails, like energy saving, ability of the green roof to provide water retention and to filter the pollutants present in precipitation. Moreover, what results from the research is that not only this system allows to reach environmental improvement, but it also brings to a decrease of the loads bearing on the structure with positive repercussions on the building.