In the context of an increasing number of retrofitting projects and greater consideration for the criteria of sustainability, architects and engineers are looking for a global optimization of existing buildings and therefore need to multiply comparisons between different possible variants. In order to structure the approach of this complex process, research carried out with the support of the Swiss Academy of Engineering Sciences (SATW) and the Swiss National Energy Research Foundation (NEFF) in the framework of the European Master in Architecture and Sustainability has made it possible to develop a multicriteria assessment methodology for office building retrofitting strategies applied to different case studies. The present article presents a synthesis of this research and an explanation of the method as a contribution to a global vision of the retrofitting process.