A vault cap is one of the curved surfaces (segments) from which a vault is constructed — the triangular or arched surface between the ribs or groins of a groin or rib vault. In a groin vault, there are four vault caps that together form the ceiling.
Vault cap in context
A groin vault is created where two barrel vaults intersect. Along the intersecting lines run the vault ribs (or groins), and the four curved surfaces between them are the vault caps.
Schematically:
- Vault rib — the projecting arch on the line of intersection
- Vault cap — the curved surface between the ribs
- Keystone — the closing stone at the centre, where the ribs meet
Types of vault caps
| Type | Shape of the cap |
|---|---|
| **Barrel cap** | Semicircularly curved, like a half cylinder |
| **Pointed cap** | Pointed curve, characteristic of Gothic vaults |
| **Dome cap** | Spherically curved segment |
| **Cloister cap** | Curved inward (concave) |
Construction
The vault cap is the thinnest part of the vault. In traditional construction:
- Built up in brick or natural stone on a timber formwork (centreing)
- The stones are laid in arch bond, with narrow joints on the inside and wider joints on the upper side
- After the mortar has cured, the formwork is removed
Identification
In a cellar or church, you can recognise the vault caps as the curved ceiling surfaces between the ribs or groins. They run from the springing point (wall) to the highest point (the keystone).
Related terms
- Vault
- Vault rib
- Keystone
- Springing point
- Groin vault