A mitre arch — also called a triangular arch (Dutch: keperboog) — is an arch or vaulting in isosceles-triangle form, like an inverted V. It is made from two straight blocks of stone set diagonally against each other, meeting in a point at the top.
Form and function
Strictly speaking a mitre arch is not a true arch with a curved line but a triangular span:
- Two sloping sides — sometimes each a single stone, leaning against each other and supporting one another at the apex.
- Small span — because the sides are often a single stone, the width that can be spanned is limited.
- Compression action — the two stones lean together and carry the load diagonally to the supports.
The Dutch name “keper”, like the related “chevron”, comes from a diagonally placed element; the word was originally used for a sloping beam in a roof structure.
Application
- Small windows and niches — the triangular form closes off a narrow opening.
- Candle niches — in the Middle Ages the mitre arch was used above small (candle) niches.
- Decorative finish — related to the corbie gable coping, a chevron-shaped finish of masonry.
Points to watch
- Suitable only for small spans; for wider openings a true (segmental or round) arch is needed.
- The sloping stones must meet well, otherwise there is no stable transfer of compression.
Related terms
- Arch
- Corbie step
- Vault
- Niche
- Bricklaying
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