Abstract Green roofs are increasingly being used to improve the energy balance and stormwater management of buildings. This work examines the thermal behaviour, water drainage and vegetation growth of two green roof systems: a conventional system containing extruded polystyrene and polyethylene, and an alternative cork-based system. In the new system, an eco-friendly expanded cork layer is used to provide thermal resistance and water storage capacity in a more sustainable way, as cork is a natural material. This material can also be used as an uncoated finishing layer for architectural purposes. The main goal of this work was to see if the new system is reliable in real environmental conditions and to compare its behaviour to that of the conventional system for a full year. This work presents the results of a fully functioning prototype built in Portugal with a technical substrate 10 cm thick and planted with a variety of vegetation. The reference and proposed systems were installed side by side and monitored under spring, summer, autumn and winter conditions. The thermal insulation and the water drainage and storage capacity provided by the cork-based green roof were found to be similar to those of the reference solution, with the expanded cork layer showing a more marked temperature delay and a more effective management of rainfall events under dry conditions. Additionally, it was found that the growth and health of plants in the cork-based green roof were comparable to those of the reference solution, indicating the good performance of the cork system.