A wall arch — also called a formeret or wall rib — is the arch by which a vault meets the rising wall: it lies against or within the wall plane and carries the edge of the vault cell. It is in effect a transverse arch placed against the wall, and so forms part of that wall. The Dutch term muraalboog comes from the Latin murus, wall. It belongs above all to Romanesque and Gothic church architecture.
Where it sits in the vault
In a rib vault four kinds of arch are distinguished:
- Diagonal ribs — the two ribs running corner to corner across the bay
- Transverse arches — the arches across the length of the building, between two bays
- Wall arches (formerets) — the arches along the side walls, in the plane of the wall
- Lunette or wall panel — the wall surface closed off by the wall arch, usually containing the window
The wall arch therefore bounds the vault cell on the wall side and makes it possible to place a window beneath the vault without weakening the structure.
Application
- Forces. The vault thrusts outwards. The wall arch carries that thrust to the wall piers and from there to buttresses or flying buttresses. A window opening therefore always sits between the load-bearing points, not on them
- Recognising it. Look up along the side wall of a church: the arch separating the vault from the wall and spanning the window is the wall arch
- Cracking. Cracks running along a wall arch indicate movement at the vault springing — through settlement, or through failing tie rods. This is always work for a structural engineer with conservation experience
- Conversion. Churches converted to new uses often gain new floors or partitions. Never load a wall arch with point loads and do not drill into one without investigation: it is a load-bearing part of the vault system
Related terms
- Vault
- Transverse arch
- Rib vault
- Vault rib
- Keystone
- Trough vault
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