Physical, chemical and hydraulic characterization of different green roof growing media

Green roofs are widespread in northern Europe and in recent years they are receiving great attention also in Italy, due to their important benefits, including urban climate mitigation and rainfall retention. In the green roof technology the substrate plays a decisive role in guaranteeing performance of vegetation and storm water management, and the main regulations governing this topic (FLL-2008, UNI 11235:2015, MT 3700:2017) provide precise indications about its chemical and physical properties. In the LifeMedGreenRoof project (LIFE12ENV/MT/000732) a significant activity was carried out in order to identify innovations that may improve the substrate performance, mainly in terms of long stability and water management. Six different substrates (two with wood biochar) have been selected and characterized for their chemical and physical properties, according to the Italian and German standards for growing media (UNI 11235:2015 and FLL-2008), focusing above all on their hydraulic performance. Such substrates were also tested in a rainfall simulator for the determination of runoff coefficient, comparing water availability data obtained in the rainfall simulator with those derived from the usual laboratory protocol (UNI EN). Many differences among substrates about their physical, chemical and hydraulic properties arose. The presence of biochar positively influenced water availability and some chemical properties.