FAN VAULT  , in architecture, a method of vaulting used in the Perpendicular style, of which the earliest example is found in the cloisters of Gloucester cathedral, built towards the close of the 14th century . The ribs are all of one curve and equidistant, and their divergency, resembling that of an open fan, has suggested the name . One of the finest examples, though of later date (1640), is the vault over the staircase of Christ Church, Oxford . For the origin of its development see VAULT .