The main task of the present project proposal is sustainable energy renovation by introducing integrated energy efficiency measures in residential building, subject of the present project proposal. The implementation of the project activities will improve the living conditions of households and will help to achieve a higher quality of the living environment, will contribute to high thermal comfort in connection with the reduced emissions of greenhouse gases, as well as to the reduction of energy consumption in the building. Improving EE will have long-term positive effects on the economy as well. The planned interventions and the reduction of energy costs for households will contribute to increasing social sustainability in many aspects, improving the living conditions of households, increasing the quality of life of the population in connection with reduced greenhouse gas emissions. The parallel efforts of national and local authorities as well as consumers to increase energy efficiency are extremely necessary given the high levels of energy intensity of the economy, exceeding 3.5 times the energy expenditure for production per unit of GDP on average in the EU, as well as given the extremely unfavorable energy characteristics of the country's building stock with predominant energy consumption classes E, F and G. Efforts to renew the building stock are essential to support economic recovery by creating jobs in the construction sector, energy savings, healthier living conditions and reducing energy poverty. In this regard, the project is in full compliance with Bulgaria's regulations in the field of EE, as well as mainly with the Strategy for Sustainable Energy Development of the Republic of Bulgaria until 2030 with a horizon of 2050, namely the achievement of a highly energy-efficient and decarbonized built fund by improving the energy performance of multi-family residential buildings.