Philadelphia’s urban renewal era left behind an east-west cut through the city’s urban fabric in the form of the sunken Vine Street Expressway. The highway construction sliced through the city’s Chinatown neighborhood, creating many small lots that are difficult to occupy and currently underutilized as surface parking. XS House places seven apartments on one such leftover site. Its extremely narrow 11-foot-wide by 93-foot-long parcel is strategically expanded through bays, mezzanines, and bi-level upper units.