Within the framework of the building section, the existing building stock is a research area with a high potential for energy savings, as it is a crucial energy consumption source. Studies are being carried out on many existing building stocks to prevent and reduce the increasing energy consumption and negative situations due to climate change and global warming. It is seen that parameters such as energy efficiency are considered as a whole with conservation in intervention methods, especially in European countries, since only conservation is insufficient for historical buildings, which are one of the primary sources of important existing building stock. Preserving cultural identity values and energy efficiency are the primary intervention criteria. By considering these two intervention criteria in balance and as a whole, the permanence and sustainability of the buildings for future generations is ensured. In this regard, comprehensive, large-scale, and multinational projects supported by the European Union (EU), especially in European countries, are carried out. In line with the conclusions drawn from the detailed and systematic analysis, comparison, and evaluation of the projects, the study proposed an approach and intervention model for future studies. The determined projects were examined in detail regarding purpose, scope, target, strategy, content, and project outcome outputs. Systematic inferences were made through the analysis in line with the data obtained. Comparisons and evaluations were made on approach information, objectives, analysis methods, technology and software used, active-passive and renewable energy systems, monitoring and tracking systems, and project output data obtained at the project's end to make the intervention's effects sustainable. As a result, a comprehensive approach model for energy-efficient retrofitting intervention approaches has been proposed in line with the conclusions obtained from the analysis, comparison, and evaluations of energy-efficient retrofitting of historic buildings. Thus, the approach model obtained with the study will guide the creation of intervention models for the studies to be carried out on energy-efficient retrofits in historical buildings.