Castle or Shiro

The Castle/Shiro wood joint is a traditional Japanese wood joining technique that was commonly used in structural elements of buildings like castles, temples, and shrines. To make the joint, wedge-shaped interlocking cuts are made on the end grains of two pieces of wood, so that when joined their grains are oriented perpendicular to each other - one vertical and one horizontal. This creates a strong, interlocking form similar to an arrowhead or V-shape. The joint derives its strength from the perpendicular grain orientation, which provides excellent torsional and shear strength even without adhesives - qualities that make it well-suited to resisting seismic forces. In addition to its structural integrity, the Castle/Shiro joint was also valued for its aesthetic appearance, with the clean, sharp lines of the tight-fitting wedges highlighting the joiner's craftsmanship. Due to its frequent usage in load-bearing structures of castles in particular, this type of Japanese wood joint came to be known as both the "Castle joint" as well as the traditional "Shiro joint".