**1. Introduction**

The application of rooftop gardens onbuildings, or green roofs [1], which introduces a layer of vegetation, growing media and an additional drainage/auxiliary layers, has evidenced to improve storm water managemen<sup>t</sup> [2,3], but this is not the only positive outcome resulting from these systems. They also produce positive impacts in many other aspects [4], such as reducing the heat island effect by decreasing the temperature in main city centers [5,6], ameliorating air pollution [7] and reducing energy consumption of buildings [8–10]. In relation to this last aspect, roofs are a critical part of the building envelopes, since they are highly susceptible to solar radiation and other environmental changes. Thereby, they have a significant influence on the indoor comfort conditions of the occupants. Roofs account for large amounts of heat gains and losses, especially onone-floor buildings with large roof area. In these cases, green roofs improve the performance of the building's energy behavior by either decreasing the heat load during the winter period [11] or the cooling requirements during summer time [12]. Green roofs also reduce the temperature fluctuation of the roof membrane along the year [13] and, consequently, increase the efficiency of photovoltaic (PV) systems installed on the roof [14]. In summary, a green roof is a good alternative to improve sustainability in urban areas by reducing energy consumption, heat stress, air pollution and CO2 emissions.

All these possibilities, and the fact that thermal behavior of a building and thus, the impact of green roof installation on the building energy consumption is not an easy subject, explain the important effort developed during the last decade for research on these systems, both from the theoretical simulation and the experimental point of view [15].Thermal conductivity of employed materials is an important factor, but other factors, such as internal loads (lights, computers, people etc.) or roof reflectance to solar radiation, can play a very important role, especially in the summer period. Therefore, the contribution of the green roof to the improvement of the energy efficiency in the building will be highly dependent on local conditions and studies should be addressed to model and experimentally quantify that contribution for different climate areas. Thusfar, published works have focusedon cold [11,16] and hot climates [12,17] applications. In this last case, special emphasis has been given to the Mediterranean area [18]. Other research studies in the area indicate the benefits of integrating green roofs onbuildings, contributing to reduce a building's energy use while mitigating greenhouse gases (GHG) in urban areas [19–21].

This paper summarizes a long-term study using a green roof designed, built and installed ona public building located in the Mediterranean coast of Spain. The main emphasis of the study was to deduce its impact on the energy consumption of the building's air conditioning system by monitoring key energy and environmental variables, covering winter and summer periods. This approach allows evaluating the energy consumption of the building and address a complete comparison for similar periods before and after the installation of the green roof. Simulation studies using commercial software TRNSYS 17 allow for the extrapolation of the results to the entire year. Obtained results are representative for buildings in theMediterranean climate area. Section 2 introduces the experimental setup used for this study, while the main experimental results are presented in Section 3. Section 4 includes an extrapolation of these experimental results to the entire year period using commercial software TRNSYS 17.
