This article aims to evaluate the potential application of prefabricated panels in energy retrofi t of facades in the Portuguese building stock. The fundamentals of this study were part of Annex 50, which was an international ECBCS IEA project, with the purpose of developing an innovative concept of building renovation for the most representative buildings based on prefabricated systems. To analyze the potential application of energy retrofi t using prefabricated panels, was important to know the reality of the existing building stock and its morphology. To know the reality of the building stock, an analysis was done based on the existing statistical data and to fi nd the most representative residential buildings, target of the study, three criteria were defi ned: buildings built before 1990, with 2 to 6 fl oors and with renovation needs in the exterior envelope. In the absence of statistical information about buildings morphology, a research work was done in the fi eld. During the collection of data a methodology was developed in which each opening was classifi ed according to a code with three parameters. In the end of the classifi cation, 29 fi nal codes were achieved and was verifi ed that three types of panels have a higher probability of being applied.