The problem of energy certification in the housing stock remains a priority for the European Community Member states referring to the European Directive N. 93/76/EEC. It is also a certainty that the potential for energy conservation in the existing buildings is very large, and there is a need for a rating of their energy performance. Facing this problem and the lack of tools, we chose to develop a measurement based approach, often referred to as an identification method. The principle of this method is to derive the thermal behavior from a continuous recording of internal temperature within the building in response to outdoor climate (temperature and solar radiation) and internal loads (heating and appliances). The derived parameters are then used to calculate a normalized heating annual consumption (NHAC) for a standard climate and a standard operation of the building (set point temperature, air change rate and casual gains). The paper presents the proposed methodology for single family houses, including the experimental equipment, the monitoring protocol and the calculation tool. Results are also discussed for a set of 10 monitored houses within Europe. Although some limitations of the methodology were found, that will require deeper investigations, the NHAC was found a robust indicator to deal with occupants' influence. (C) 2001 Elsevier Science B.V. All rights reserved.