A panel actuated by a Shape Memory Alloys (SMA) wire is proposed for building envelopes, in particular ventilated façades, and is aimed at improving architectural and energetic performances of buildings. The SMA is used with two purposes: energy-free thermal sensors (not requiring electric current or other energy sources to be activated), and actuators where the movement is due to the large amount of energy produced by phase changing associated with thermal variations. During summer, façade panels open to allow natural ventilation in the cavity in between the external façade and the internal wall, while during winter panels close for building thermal insulation, provided by the still air in the cavity. We investigate the theoretical background behind the panel idea, and then we develop a prototype where its practical feasibility is shown. The material is Aluminum for the panel and Nitinol (Ni-Ti) for the wire providing the necessary force to open the panel. The final aim is the achievement of a sustainable façade that reacts to thermal variations without energy supply.