The preservation of post-war architecture represents a complex challenge to overcome for different reasons: hesitating recognition, bad perception and a certain material fragility. Especially the economic post-war housing has difficulties to be recognized as an architectural heritage worth to preserve. This thesis analyses the phenomenon through case studies, selected within the oeuvre of a representative architect of the period, Georges Candilis, and addresses their current state. The first part of the present thesis is dedicated to the life and work of Georges Candilis and hence allows to distinguish the competition ¿Opération Million¿ as a key element of his prolific oeuvre concerning construction for the greatest number. This competition, launched by the French government in 1955 in the aftermath of the abbot Pierre¿s appeal during full on housing crises, marks the beginning of the success of the office Candilis-Josic-Woods. The second part begins with the current state of the ¿Million¿ buildings which is more than deplorable: the majority is demolished or turned unrecognizable after important rehabilitation measures in order to respond to energetic regulations being more and more restrictive. The balance of all identified buildings during this research allowed to define five intervention strategies: demolition, heavy intervention, intermediate intervention, light intervention, preservation. The following five case studies represent these five strategies: the building ¿116¿ in Persan, the cité du Bois Matar in Villeneuve-Saint-Georges, La Louvière in Rambouillet, the cité Jean-Baptiste Renoult in Ivry-sur-Seine and the cité de l¿Etoile in Bobigny. Hygrothermal simulations are set up with the goal to analyse the existing interventions and to evaluate their energetic performance in a quantitative way. The third part focusses on these simulations. This last part is concluded by a presentation of alternatives and recommendations proposing a middle ground between architectural quality and energetic requirements on the building envelope. Thus, the corpus of this work presents three very different parts that offer a global approach, started from the up-to-dateness, to an architectural heritage that is neglected and that would deserve an incontestable recognition.