In an ambitious tertiary program, within highly demanding constraints, we tried to generate a compact building with an efficient relationship between the surface of the skin and the surfaces of the floors. The nature of this skin confirms a strong energy strategy. It is a bearing facade, isolated from the outside and dressed in a glass skin naturally ventilated. Such thick skin confers to the building an excellent thermal inertia by restricting the exchanges between inside and outside in order to smooth thermal cycles. The envelope expresses by its architectural concept the critical relation [full / empty = approximately 50 %] by the systematic alternation of an opaque module façade with a transparent module of identical dimensions. In the same way, particularly in the South, the choice of an adapted solar protection, according to a detailed analysis of the solar contributions, affirms the consideration of energy issues including those due to overheating by solar radiation. In order to be integrated in the global program of the ZAC Claude Bernard, the design of the ground floor enlarges transparencies from the boulevard McDonald towards “the linear forest”. An architectural process for specific glass screen will hide the technical contingencies related to the operation of the building. The level of attic was also the object of a particular attention in its volume in order to create a signal, a visual identity for the ZAC Claude Bernard from the ring road of Paris.