This article deals with a new configuration using a phase change material (PCM) in a complex roof on a dedicated test cell. For the first time and in real conditions, an experimental device using phase change material was set up for a tropical and humid climate such as that in Reunion Island. Results showed that in the configurations tested and for a non-ventilated air layer, the measured temperatures were on either side of the PCM’s melting point. It means that the PCM is able to store thermal energy in the daytime and release it at night. Furthermore, this study has made it possible to determine the thermal resistance of the roof via a mean method meeting international standards (ISO 9869) using dynamic data. The test was implemented in a multi-zone building software in order to automatically determine the thermal indicator.