The European Green Deal and others European Regulations designed to encourage building sectors to increase building energy efficiency towards achieving climate neutrality by 2050. Buildings account for about 40% of global energy consumption. In the European Union, 85% of buildings were built before 2000, and 75% of these have low energy efficiency. A significant number of these structures, between 85% and 95%, are expected to remain in use by 2050. Therefore, the building sector is vital to Europe’s decarbonization efforts. This paper discusses the context of assessing the level of energy efficiency of the existing buildings sector. The methodology is based on issued energy performance certificates and real data on the building’s primary energy demand. In the course of the analysis of energy performance certificates, deficiencies were found that the determined primary energy demand data do not always reflect the real situation, as energy auditors use unverified data and Latvian legislation does not verify them. This is a significant shortcoming and can only be eliminated at the national level by introducing amendments to the Law on Energy Efficiency of Buildings. This article aims to help future researchers address existing gaps and contribute to advancing the field.