This paper consists of theoretical research and a practical part. In the theoretical – research part, the characteristics of the Simprolit system products are given. In the practical part, an assessment of the building of the restaurant „Košutnjak“ in Kragujevac was made. After a detailed visual inspection of the building, the type, the cause, and the degree of occurred damage were determined and the measures for their repair were also. Then, the calculation of the energy efficiency of the building in its current state was performed, with the determination of the energy class. Finally, energy rehabilitation measures were proposed and the calculation of energy efficiency was repeated. The energy efficiency of the building is significantly improved by the suggested measures.