The main category of residential building through 120th and 150th street is cooperative houses built 100 years ago, and most of them are already in disrepair. The main issues are security problems and loss of indoor public space compared to modern luxury buildings. I want to redefine those unoccupied interstitial spaces and transform them into collective public space including amenities like a gym, reading space, and gathering space. The project allows me to engage and invest architecturally in the dichotomy of inside-outside through the lens of urban planning. By clarifying the different levels of privacy and defining how the two circulations intertwine, that allow the public to access the programmatic elements without disturbing residents living there. The privacy level changes vertically. Two scissor stairs merge on the rooftop. In the 1 to 1 physical model, I chose to realize the core wall facade system, which consists of a concrete panel including nine pieces of concrete transparent bricks.