Wind brace

Trelystan Church, Montgomeryshire. Decorative arched wind braces between purlins- 15th-16th century

In architecture, wind braces are diagonal braces to tie the rafters of a roof together and prevent racking. In medieval roofs they are arched, and run from the principal rafters to catch the purlins.^[1]

References

1.  One or more of the preceding sentences incorporates text from a publication now in the public domain: Chisholm, Hugh, ed. (1911). "Wind Braces". Encyclopædia Britannica. Vol. 28 (11th ed.). Cambridge University Press. p. 708.