Novel application and reused materials for extensive green roof substrates and drainage layers in Japan ? Plant growth and moisture uptake implementation

This study investigates the potential utility of reused materials as an alternative material for commercial substrate and drainage layers. The performances of reused materials were assessed using turf with trays on a roof for two years in Chiba, Japan. Two types of materials, a commercial green roof substrate and cocopeat, were used as the substrate. For the drainage layers, five different materials were used: a commercial green roof drainage layer, bamboo stems and nodes, and polyethylene terephthalate (PET) bottle caps and bottoms. In addition, a sample without any drainage layer was used. The trays were prepared with the combination of these two substrates and six drainage applications. Overall, reused materials were observed to function well as commercial green roof materials. The turf in cocopeat was able to survive better than turf in commercial green roof substrate. In the drainage layers, some reused materials, such as the PET bottle caps and bamboo nodes, showed higher final plant coverage than commercial drainage layers in cocopeat. Our study has addressed the importance of realizing the original substrate and drainage layer using reused materials for developing sustainable and inexpensive green roofs.