In the national context, Italy with the Integrated National Plan for Energy and Climate (PNIEC) intends to achieve an indicative target of reducing consumption by 2030 equal to 43% of primary energy and 39.7% of final energy compared to the reference scenario of 2007 while with the National Recovery and Resilience Plan (PNRR), the ecological transition will have to be the basis of the new development model on a global scale. To start it up, it will be necessary to drastically reduce emissions of climate-altering gases in line with the objectives of the European Green Deal. Secondly, it will be necessary to improve the energy efficiency of production chains, civil settlements and public buildings and the quality of air in urban centres and water. In light of these ambitious objectives, particular attention is paid to existing buildings: this research has been focused on the is the National Boarding School “Mario Pagano”, an 8,700 m2 school built in 1899, located in the historical centre of Campobasso (Molise). The effects of the intervention proposals have been simulated in order to evaluate energy savings and the reduction of CO2 emissions. The research is also supported by an economic evaluation that prove the economic sustainability within a period of about 15 years.