The city of Lausanne is built on fairly steep slopes, with the consequence that some buildings are leaning against what could be described as cliffs and, therefore, have only one glazed facade. The Rue Saint Martin office building has been built during the 1970s. Because of its important depth (similar to 23m from the facade), the spaces located at the back were totally deprived of natural light. During the renovation of this building, the architects wanted to create large openings in the roof and in the floors' slabs in order to provide daylight to the rear spaces. The close collaboration between Estia(1) and Archespace(2) allowed for the design and implementation of an efficient daylighting system that provides a new quality of use for the interior spaces and a new identity for the building.