Based on the unsatisfactory energy audit for the thermal technology of the building, it was necessary to carry out additional insulation of the building according to the requirement for external thermal insulation contact systems (ETICS) for quality class A according to TP CZB 01-2015. The reduction of energy consumption also included the complete replacement of non-compliant window filler panels, both plastic and aluminium. Furthermore, the construction included modification of the existing internal sewage system and modification of the electrical wiring, specifically the power current. The central heating system was also modified in the classrooms. Another requirement of the investor was to meet the request of comfort ventilation in the school classrooms (forced fresh air supply and exhaust of degraded air – equal pressure ventilation) according to which the installation of compact ventilation units with heat recovery was carried out.