Increase in energy efficiency and reduction of greenhouse gas emissions of buildings can be achieved through improvements made in the existing stock of buildings. Therefore, one of the objectives for incentive policies should be to promote environmental issues each time a rehabilitation process is engaged. Specific tools have to be developed for that purpose. In this paper, we present a 3D Geographical Information System (3D GIS) designed to evaluate the environmental properties of buildings envelopes, in order to assess their improvement potentials. The system offers a representation of the entities that compose the building, and its associated environmental data (solar data, energetic and sonic ones, architectural data, etc). These are obtained either by observation in situ or by simulation. The system facilitates data handling and data crossing to optimize analytical process. An evaluation of its functionalities is in progress in the city of Nantes (West of France).