Urban greenery is universally recognized as a mitigator against environmental problems. It's indeed in the cities - where lies the highest concentration of anthropogenic activities - that the effects of pollution and uncontrolled urbanization have caused more damage, with the known phenomenon of "heat islands", especially in the metropolises, undermining the inhabitants' quality of life. Numerous data collection on urban dimensions and specific indicators reveal the significant paucity of green spaces in urban realities. So how could greenery be implemented, especially in contexts where sealing and paving of outdoor spaces (squares, parking lots, etc.) have reduced the availability of natural soil? A simple but effective solution can be offered by the verticalization of green spaces, where the green areas are not only capable of purifying the environment through the retention of CO2 and particulate matter, but also of improving the building energy performance: the design proposal of the ‘Living Wall’ on the facade of a public building serves exactly this scope. An analysis of the perimeter surface has been carried out in order to identify and measure the comparison energy efficiency parameters before and after the proposed intervention. A simulation has confirmed the improvement of the building energy performance: the transmittance values, other than complying with the verification procedure as stated in the Italian decree DM 26.06.2015, show a significant reduction with those of the actual state and are decreased by almost half if compared to the case when only the insulation has been applied. The model has shown beneficial effects even on the thermal phase shift, a key parameter for both summer comfort and energy savings. Much of the heat affecting the building is absorbed in the daytime (retaining it but keeping it out of the internal rooms) and then gradually released in the nighttime when the external heat has subsided.