The gap between calculated and actual energy use has long be recognized as a major hurdle for a realistic assessment of buildings' performance and anticipated benefits from energy conservation measures, especially when attempting a national building stock analysis. A multinational European effort to develop a conceptual framework for monitoring the effectiveness of energy retrofit measures applied in the European housing sector has motivated a number of national pilot actions. This paper presents the results from the work carried out in Greece and elaborates a methodology for deriving different empirical adaptation factors that relate the normative calculated heating energy consumption from energy performance certificates (EPC) with the actual energy use. To gain some additional insight, the work is complemented by evidence from field surveys to collect actual energy use data from dwellings before and after refurbishment and behavioural surveys of occupants. The derived factors are used to adapt the predictions, which are then organized according to the Hellenic residential building typology. The overall approach is used with a building stock model to demonstrate a preliminary assessment of different energy conservation measures, towards meeting the national targets for 2020 and 2030. The ratio of actual to calculated primary energy consumption using the processed EPC data from over 8500 dwellings, averages 0.56 (i.e. 44% lower energy use than calculated). Findings from field surveys of occupant behavioural changes in the operation of space heating systems, confirm poor indoor thermal comfort conditions resulting from reduced operating hours of space heating, lower thermostat settings etc., which deviate significantly from normative calculation assumptions. Other field data on actual energy use before and after refurbishment provide additional insight for adapting the predicted savings as a result of common retrofit actions. Popular measures include for older buildings the installation of double glazed windows, the replacement of heat production systems and roof thermal insulation. On average, the weather corrected actual primary heating energy savings are about 21% by installing double glazed windows and about 18% by replacing an oil-fired boiler with a new natural gas unit. The application of the results with a building stock model illustrates that future energy and emission targets could be reached with the conservative adaptation factors, but will mandate combined measures and more aggressive modernization rates using an average trend scenario. (C) 2015 Elsevier Ltd. All rights reserved.