structural:reformatting, information:classification
Structure

The chapel is about 35 metres (118 feet) long and 14 m (46 ft) wide, with the ceiling rising to about 20 m (66 ft) above the main floor.

Its exterior is unadorned by architectural or decorative details, as is common in many Italian churches of the Medieval and Renaissance eras. It has no exterior façade or exterior processional doorways, as the ingress has always been from internal rooms within the Apostolic Palace (Papal Palace), and the exterior can be seen only from nearby windows and light-wells in the palace. Subsidence and cracking of masonry also have affected the Cappella Maggiore, necessitating the building of very large buttresses to brace the exterior walls. The accretion of other buildings has further altered the exterior appearance of the chapel.

The building is divided into three stories of which the lowest is a very tall basement level with several utilitarian windows and a doorway giving onto the exterior court. Internally, the basement is robustly vaulted to support the chapel. The building had six tall arched windows down each side and two at either end, several of which have been blocked. Above the vault is a third story with wardrooms for guards. At this level, an open projecting gangway was constructed, which encircled the building supported on an arcade springing from the walls. The gangway has been roofed as it was a continual source of water leaking into the vault of the chapel.