Barrel Roof (Barrel Vault)

A barrel roof has a semicircular or segmental cross-section extended along the length of the building, like a barrel or tunnel cut lengthwise. In masonry, the structure is called a barrel vault, also known as a tunnel vault or wagon vault; effectively it is a series of arches placed side by side. In modern buildings the same curved profile is produced in steel, timber, glue-laminated arches, curved metal sheeting or polycarbonate, and is often simply called a curved or arched roof.

History

• The earliest known example is a tunnel vault beneath a Sumerian ziggurat at Nippur, dated to around 4000 BC.
• Egyptian builders used tunnel vaults from about 3500 BC, mostly for underground passages, and the Ramesseum mortuary temple was vaulted in this way.
• The Romans used barrel vaults widely but increasingly favoured groin vaults, which need thinner supporting walls and allow more openings.
• Barrel vaults returned in medieval Romanesque churches such as Cluny Abbey, gave way to ribbed vaults in Gothic cathedrals, and were revived in the Renaissance and Baroque, including at St Peter's Basilica.
• In the 20th century, Louis Kahn's Kimbell Art Museum in Texas used a series of vaults.

Structural behaviour

A barrel vault pushes outward along its full length, so the supporting walls must be thick, buttressed or tied, or the thrust must be balanced by adjacent vaults. Intersecting two barrel vaults at right angles creates a groin vault.

Modern curved roofs

Curved metal roofs, either crimp-curved profiled sheets or curved standing-seam panels, are used on houses, Dutch barn conversions, sports halls and industrial buildings. Curved roofs pair well with metals such as zinc. Lightweight arched steel buildings, including military huts, use a similar profile. Drainage is straightforward because water flows down both sides, but the flatter crown can require a covering suited to low slopes.