One of the main goals of building design is indoor comfort, regardless of its use (residential, educational, institutional, etc…). However, to achieve indoor comfort, buildings require a significant amount of energy. In the last decades, designers and researchers have been studying new strategies to improve buildings’ energy efficiency, with the purpose of mitigating the negative environmental impact caused by heavy energy consumption. Green roofs have been one of the most investigated solutions because of the many thermal benefits they can offer, and amongst these, hydroponic green roofs gained momentum. This study aims to analyse the rooftop temperature reduction provided during the hot months by a hydroponic green roof, compared to a traditional roof slab and an extensive green roof, in order to assess the different performances of these systems. In situ experiments were conducted to collect surface temperature of the roof slab during summer, with and without the hydroponic system, in order to assess the potential temperature reduction, which subsequently affects the heat flow through the roof and therefore the indoor air temperature. The results show a significant decrease in the external surface temperature of the roof compared to the bare roof, but also slightly better performance compared to the extensive green roof. Despite first promising results, the knowledge on hydroponic green roofs performance remains limited and some drawbacks need to be assessed. For these reasons, further in situ testing should be carried out, under different climatic conditions and experimental setups.