Add another room to your main whelping box. Multiple rooms can be daisy-chained together. A 4x4 room can be added to a 4x6 room, and vice versa. A 3x3 add-on room can only be added on to 3x3 Fab boxes. Add-on rooms allow the breeder to teach proper feeding habits, socialization, and house training. Doors are fully functional between room