A rib vault is a cross vault in which stone ribs run along the diagonals and carry the vault. Where a groin vault has only a groin — the line where two vault surfaces meet — the rib vault turns that diagonal into a structural member in its own right. It is the vault of the Gothic period.
Why ribs?
The advance lies in the building process. A groin vault has to be built in one operation on timber centering that supports the whole vault surface — a great deal of timber, a great deal of work, and none of it can be struck until the whole has cured.
A rib vault works differently:
- First the ribs are built on narrow, curved centres — supporting only the ribs themselves.
- At the top the keystone is set, locking the ribs together.
- The ribs then carry the infill: the vault webs between the ribs are built more lightly, often in thin or lightweight stone.
This saves a great deal of centering timber, and the centres can be moved on to the next bay. The webs themselves no longer need to be heavy masonry either, which reduces the total weight — and so the load on walls and buttresses.
What you can see
- The ribs are moulded. They are usually dressed stone with a pronounced profile; the infill is often brick or plastered.
- The keystone. A boss sits at the intersection, frequently carved with a coat of arms, a rose or a figure.
- The springing. At the bottom the ribs gather on a corbel, a capital or a compound pier. That point carries everything.
- Elaboration. In the late Gothic, additional ribs appear: liernes, tiercerons and eventually full net and star vaults.
When inspecting
Cracks in the webs are often less alarming than cracks or movement in the ribs and at the springing points: the ribs are the structure. Also watch for walls leaning outwards and check the condition of any tie rods — the vault pushes sideways, and that thrust has to be taken somewhere.
Inspecting a rib vault: what to check
- Ribs and springing points: Cracks or movement here are often more alarming than cracks in the webs: the ribs are the structure.
- Walls: Watch for walls leaning outwards.
- Tie rods: Check the condition of any tie rods: the vault pushes sideways, and that thrust has to be taken somewhere.
Related terms
- Groin vault
- Vault rib
- Vault web
- Vault keystone
- Vault bay
- Buttress
- Gothic
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