This article describes the application of a method of environmental certification of buildings used in Brazil and named as Brazilian Labelling Program PBE–Edifica. The method was developed by Procel, National Electric Energy Conservation Program, which confers, four Labels of the Energy Efficiency levels of a building, covering the Envelope; the Lighting System; the Indoor Air Conditioning; and the building Overall, which includes all previous levels and bonuses. The levels and scope of the Label apply both in the design phase and after construction or existing building in accordance with the Technical Quality Regulation for the Level of Energy Efficiency for Commercial, Service and Public Buildings, RTQ-C. The efficiency level ranges from A to E, where A is the most efficient and E the least efficient. The method also considers Bonuses that allow improvements in the Overall Classification efficiency. Thus, the objective of the research carried out was to identify the classification of the level of energy efficiency of an existing building on the campus of the Federal University of São Carlos, the Community Library, called BCo, Brazil built in 1995 with an area of 6,947.48 m2. The guidelines of the PBE Edifica using the prescriptive method were applied, and the characterization of the level of energy efficiency was carried out based on data obtained from plans and technical drawings of the building, and through a technical visit to obtain the data for entry into an application, WebPrescriptive. To obtain specific information about the wall's thermal transmittance and roof solar absorbance the PROJETEE application was used. All information processed so the building obtained an Overall classification C. For envelope and lighting level E, and air conditioning level B. To improve the level of efficiency, through bonuses, improvements in the lighting system and the elevator were suggested, resulting in level B for both Lighting and Overall efficiency. Notice that the building, due to its design and construction system does not have the conditions to reach level A of efficiency. In conclusion, we would like to point out that it is feasible to submit the building to the formal labelling process, since the proposed improvements resulted in an Overall Energy Efficiency Rating B. As a contribution for EFFICACY Project, some guidelines to be considered for buildings rehabilitation will be stated, as simulation of thermal insulation in facades and others improvements.