What is a corbelled vault?

A corbelled vault (also called a false vault or pseudo-vault) is a covering that looks like a vault but is built from courses of stone, each projecting slightly further towards the centre than the one below. The courses creep towards each other from both sides until the gap at the top can be closed with a single stone or slab.

How it differs from a true vault

	True vault	Corbelled vault
Structural action	Arch action: wedge-shaped stones pass compression to the supports	Cantilever: each course projects and is held in place by the weight of the masonry behind it
Joints	Perpendicular to the curve	Horizontal
Outward thrust	Large, must be resisted	Much smaller, as there is hardly any arch action
Shape	Round, pointed or flat	Usually steep, stepped or pointed

Because each course may only project a little, a corbelled vault quickly becomes tall and steep. It suits small spans, or spaces where height is not a problem.

Where you find it

Corbelling is one of the oldest ways of roofing a space in stone. Well-known examples:

• The trulli of Apulia, Italy
• The nuraghi of Sardinia
• Prehistoric passage tombs in Ireland, such as Newgrange
• The tholos tombs at Mycenae
• Vaults in Maya architecture

Practical points

• Corbelled masonry needs counterweight. If an alteration removes the masonry behind or above a corbel, the projection can tip.
• Get a structural engineer involved before cutting into, propping or adding load to an old corbelled vault.
• Cracks in the bed joints and stones sagging inwards point to lost counterweight or decayed mortar.
• Repair with a compatible mortar. An overly hard cement mortar in old lime masonry can cause fresh damage.

Related terms

• Vault
• Corbel
• Dome
• Megalith
• Lime mortar

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