Among the adaptation measures against the climate change, energy saving in buildings is a crucial point. Detailed analysis to keep the operation of the building as well as its architectural features when listed is required. A school is selected as case study for its age of construction and potential of replicability due to its similarities for many other schools which make it an archetype. Building envelope and energy systems are the area of intervention supported by an experimental campaign to assess the status quo. Furthermore, the design complies with minimum environmental requirements by current regulation for public buildings. For the new proposed design, the target of high-efficient building is reachable even for so constrained existing building.