Abstract
Energy efficient design is a high priority in the national energy strategy of European countries considering the latest requirements of the European Directive on the Energy Performance of Buildings. The residential sector is responsible for a significant quantity of energy consumptions from the total amount of consumptions on a worldwide level. In residential building most of the energy consumptions are given mainly by heating, domestic hot water and lighting. Retrofitting the existing building stock offers great opportunities for reducing global energy consumptions and greenhouse gas emissions. The first part of the paper will address the need of thermal and energy retrofit of existing buildings. The second part will provide an overview on how various variables can influence the energy performance of a building that is placed in all four climatic zones from Romania. The paper is useful for specialist and designers from the construction field in understanding that buildings behave differently from the energy point of view in different climatic regions, even if the building characteristic remain the same.