The subject of this thesis was to research the effects of a ceiling renovation on the energy consumption of a detached house built in 1976. The aim was to find out the benefits of replacing thermal insulation and blocking air leakage points. The condition of the ceiling and the location of air leaks were studied by thermal imaging and measuring the air tightness. The structures were studied with the Comsol Multiphysics simulation program. Heat loss calculations were performed using MathCad Prime. The effects of the renovation on heating energy need and air tightness were studied by measuring the air leakage rate of the building before and after the renovation and calculating the reduction in the heating requirement due to the improved thermal insulation capacity and air tightness of the structure. Ekovilla blown loose wool was used as a new thermal insulation and air leakage points were blocked by Sitko Flex tape. The research provided information on the effects of ceiling renovation on energy consumption. Both the computational and measured results showed that energy renovation on the ceiling alone can achieve savings in heating costs and improve the structural physics of the structure. The original U-value calculated from the structural drawings improved from 0,20 W/m2K to 0,09 W/m2K, 55 % overall. The heat loss of the ceiling was reduced by 65% from the original. The heat loss of the entire building was reduced 10 % by repairing only the ceiling. Airflow rate n50 improved from 8.7 1/h to 6.6 1/h, 24 %, and q50 from 7.0 m3/m2h to 5.3 m3/m2h, also 24 %. According to calculations the energy consumption of the whole building was reduced by 2 241 kWh per year.