The project B5 Boulogne is part of the urban development zone called Seguin Rives de Seine near Paris. This area was formerly home to the monumental Renault factories. As a result of the delocalization of these factories, a surface of 74 hectares has been liberated. This new area named “Macrolot B5” has been divided into seven smaller blocks distributed around a large urban garden. Seven architects were selected to design seven different buildings, organized by an urban coordinator in charge of the Macrolot B5. White concrete, implemented in several ways, is the material connection between the buildings in the project. They are also connected through a common garden, located in the centre of the Macrolot B5. Not only is this generous garden visible from the surrounding streets through vaults in the buildings, but it also forms a generous ecological biotope providing calm and green views to the inhabitants. Additionally, most of the rain water is immediately treated on site to prevent over pouring the urban drain system. As a result of this, the Macrolot B5 works as an ecological hamlet, inviting people to meet, talk and reinforce a more environmental behaviour. Our building is located in the centre of the site, which was the main constraint, just as a fountain in the middle of a cloister. How could the building’s position transcend this constraint ? The pillar of our design proceeds from this principle, this central position, providing both generous indoor spaces, and outdoor spaces by gently protecting the views brought us to this design: the Boulogne Arches.