The need to have a more eco-sustainable world has steered our daily practices towards more conscious and rational energy uses. Among these activities, the construction of buildings with nearly zero energy need and the renovation of the existing ones can certainly have a large impact from an energy standpoint. In this direction, the "Energy Performance Building Directions" (EPBD) of 2010 defines the concept of a nearly zero-energy building (NZEB), although the requirements to qualify as NZEB remain ambiguous. In Italy, the NZEB concept is strongly related to a major use of renewable energy sources to cover the energy demand of the buildings.