barrel vault

Coffered ceiling of the barrel-vaulted nave in the Temple of Jupiter at Diocletian's Palace in Split, Croatia. Built early 4th century. Nave of Lisbon Cathedral with a barrel vaulted soffit. Note the absence of clerestory windows, all of the light being provided by the Rose window at one end of the vault. The Cloisters, New York City A barrel vault, also known as a tunnel vault, wagon vault or wagonhead vault, is an architectural element formed by the extrusion of a single curve (or pair of curves, in the case of a pointed barrel vault) along a given distance. The curves are typically circular in shape, lending a semi-cylindrical appearance to the total design. The barrel vault is the simplest form of a vault: effectively a series of arches placed side by side (i.e., one after another). It is a form of barrel roof.

As with all arch-based constructions, there is an outward thrust generated against the walls underneath a barrel vault. There are several mechanisms for absorbing this thrust. One is to make the walls exceedingly thick and strong – this is a primitive and sometimes unacceptable method. A more elegant method is to build two or more vaults parallel to each other; the forces of their outward thrusts will thus negate each other. This method was most often used in construction of churches, where several vaulted naves ran parallel down the length of the building. However, the outer walls of the outermost vault would still have to be quite strong or reinforced by buttressing. The third and most elegant mechanism to resist the lateral thrust was to create an intersection of two barrel vaults at right angles, thus forming a groin vault.