The buildings sector contributes to 30% of annual greenhouse gas emissions and use about 40% of energy. In this scenario and regarding the sustainable concerns, different strategies and directives have been developed, highlighting EPBD and EPBD-recast. With this last one the concept nZEB appears, and with him the promotion of the building rehabilitation sector. The strategies and the rehabilitation benefits are more and more recognized, used and increasingly considered by the stockholders. So, the aim of this article is to: critical analyse the state-of-art regarding this matter; discuss the existing solutions, directives and strategies; and present a case study where the energy performance and the economic viability are discussed. The case study is a Portuguese building model which represents the conventional construction between 1960 and 1990. On it, three scenarios of rehabilitation were tested, and their benefits and costs are presented.