Barrel vault

An arch is a curved structural form that carries loads around an opening, transferring them around the profile of the arch to abutments, jambs or piers on either side. Arch are structurally very stable in compression, as loads are relatively evenly balanced through their form.

A vault is a structural form composed of a series of arches, typically found in the construction of ceilings or roofs. The arrangement of the arches relative to one another determines the type of vault.

A barrel vault is a continuous arched shape that may approximate a semi-cylinder in form, resembling the roof of a tunnel, or may be pointed at its apex. It is typically formed by a series of arches or vaults placed side by side or by a continuous shell.

Barrel vaults are first thought to have been developed by the by the Sumerians, and were subsequently used by the Egyptians. They were used extensively in Ancient Rome for stone structures such as cisterns and aqueducts and as part of major buildings such as the Colosseum. Throughout the Middle Ages they were used across Europe as part of the construction of churches, and they continue to be a feature of modern architecture and engineering.

Barrel vaults must be able to withstand the outward pressure on the lower parts of the vault imposed by the structure above. If the barrel vault is underground, the pressure might be resisted by the ‘fill’ surrounding it. If it is above ground, the outward pressure can be resisted by thick supporting walls, although this becomes less practicable as the size of the vault increases. Additional strength can be provided in the form of supporting columns, stiffening diaphragm beams, side anchors or parallel walls that can distribute stress.

A groin vault (double barrel vault or cross vault) is formed by the intersection of two barrel vaults at right angles. The ‘groin’ is the edge between the intersecting vaults. This is a more efficient structure that only has to be restrained at its corners. A series of groin vaults can be built next to one another to create a similar effect to a simple barrel vault.

Stepped barrel vaults are formed by a series of barrel vaults at different levels.