As part of its Agenda 21 and Cit’ergie labeling, the City of Rouen is committed to strengthening its exemplarity in the fight against global warming and energy efficiency.Laureate of the call for applications "positive energy territories for green growth" (TEPCV), the city of Rouen is leading an efficient energy renovation of the City Hall, a very energy-intensive building dating from the 18th century, whose facade is classified as a historic monument.To achieve a very high level of energy performance without changing the facade, it was necessary to set up "a system of heating and managing them innovatively. This building will be heated by a boiler and cogeneration to produce electricity, will benefit from Leds lighting and a technical building management system that can be used by users. In addition, it will participate in the national CUBE 2020 competition for energy saving in tertiary buildings thanks to users. Finally, as far as possible, the materials used will be biobased.