Coarse recycled materials for the drainage and substrate layers of green roof system in dry condition: Parametric study and thermal heat transfer

Abstract

The replacement of natural materials with recycled materials for green roof systems with drainage and substrate layers has scarcely been evaluated while it can be considered as a potential solution to reduce the overuse of natural resources. Moreover, optimizing green roof layers' thickness and evaluating the thermal resistance of drainage and substrate layers in dry state have rarely been taken into account. Therefore, the aim of this work was to assess the green roof layers' thermal resistance concerning ISO 9869-1 where the drainage and dry substrate layers are substituted with coarse recycled materials. A sensitivity analysis was conducted using WUFI software to optimize the thickness of different layers. As per the results, there was a narrow difference between the Rc-value of the proposed green roof made with coarse recycled materials and that of the control green roof without coarse recycled materials, (5.3%); so, recycled materials are recommended to be used for the rooftops due to their low bulk density and light weight. Moreover, the dry substrate layer's Rc-value was about twice that of the drainage layer of coarse aggregates due to deeper thickness of the former than the latter; however, considering the same thickness for the coarse aggregates and dry substrate layers, the Rc-value of the coarse aggregates was higher. Meanwhile, by simultaneously increasing the thickness of both layers, the model with an 18-cm substrate layer and a 6-cm drainage layer adequately provided the heat retention capacity required for the green roof system.