13th + Walnut is a modular office building in Philadelphia's Center City District. By stacking 8 floors of prefabricated containers around a stair and elevator core, the long office space is created. Each container is pushed or pulled inside the zoning envelope, yielding larger office spaces or exterior terrace spaces. The design intent of the project is to create an activated exterior envelope zone. This is achieved by grafting a system of stacked interconnected terraces up front facade of the building, creating a vertical neighborhood. These terraces also occur on the rear facade of the building as well as connect to the common roof space. This envelope activation is complemented by private office space which are designed to passive house standards. The accessibility of the stacked office creates a sidewalk at every floor, which becomes a link to Walnut street below.