Abstract The objective of this article is to improve diagnosing and data availability for all stakeholders, including building operators, planners, inhabitants and utility suppliers. This paper presents the results concerning the demand for final and primary usable energy. For each of the buildings a preliminary energy audit was prepared and this was the basis for comparison between the estimated energy consumption in the buildings before and after thermal upgrading. The research was carried out mainly in buildings belonging to the Department of Public Utilities and Housing in Zielona Gora. The group of selected buildings consisted mainly of traditional technology buildings having different functions, i.e. residential, residential-commercial, commercial, and other buildings (schools and boarding houses). Forty buildings were selected for analysis. They were built in different years and had different functions, i.e.: 23 residential buildings, 6 residential commercial buildings, 7 commercial buildings, and 4 buildings had other functions (schools). They are the main energy consumers, which has a considerable impact on the environment.