This paper aims to analyse the changes that the new Hellenic Regulation on the Energy Performance of Buildings (REPB) has brought to the Hellenic residential buildings, which is in line with the European Directive 2010/31/EC. These changes refer to construction techniques, construction costs and energy performance. Our assessment is based on the numerical analysis of two typical residential buildings, a single and a multi -one. Both buildings were studied according to the requirements set before and after the application of the REPB for all (four in total) climate zones of Greece. The cost for implementing the two regulations was evaluated, as was also the energy consumption cost. Based on these costs we estimated the operating costs for heating, cooling and domestic hot water of the two buildings of this study. The implementation of the REPB significantly reduced the required heating loads for space heating in all climate zones by 37%-48% for both building types; this is mainly attributed to the improvement of the thermal properties of the building envelope and the improved energy performance of the electromechanical systems. The required cooling load was low and the implementation of the REPB did not change it significantly. Significant energy savings, in the range of 51%-58% were also achieved by installing flat plate solar collectors for Domestic Hot Water heating. (C) 2017 Elsevier B.V. All rights reserved.