peer reviewed ; Alternative materials exist for green roof layers: secondary resources like coarse or fine recycled aggregates may be used as a substitute to natural materials. For using these new types of materials, it is needed to assess their heat resistance which is performed according to ISO 9869-1 standard. Moreover, the initial hygrothermal conditions of unsaturated substrate and drainage layers have also to be modelled and assessed for optimizing the layers’ thickness. In this study, the green roofs with unsaturated substrate and drainage layers incorporating coarse recycled materials were tested and assessed. The hygrothermal conditions of unsaturated substrate and drainage layers were simulated using WUFI software. A small difference (4.2%) was observed between the Rc-value of the green roofs with and without coarse recycled materials, confirming that these materials provided a sufficient thermal resistance, similar to soil particles for the substrate layer. Considering a constant thickness for the substrate layer (15 cm), a 6-cm drainage layer with coarse aggregates was considered as the optimum design for green roof systems. Besides, 18-cm unsaturated substrate layer was the optimum design when the drainage layer’ thickness was considered constant (5 cm). The 6-cm drainage layer and 18-cm unsaturated substrate layer were definitely the best design for the roofing systems with the simultaneous change in the substrate and drainage layers’ thickness.