Shippasamitsugi

Known in English as layered multiple mortise and tenon joints, shippasamitsugi is a sophisticated traditional Japanese wooden joinery method. It involves cutting an ordered series of interlocking mortises and corresponding tenons into the ends of horizontal shippa crossbeams, which are then fitted precisely together with vertical samitae posts. Due to the alternating orientations of each layer, the grain of the beams runs perpendicular to that of the posts at each joint interface. This creates an incredibly robust structural connection as the counter-grained fibers interlock, rigidly joining the load-bearing frame while still allowing for wood movement. Through its stacked cross-grain mortise and tenon joints secured entirely by friction fit, shippasamitsugi allowed multi-story temples, castles and other important buildings to be assembled entirely from wood into enduring frameworks. Even today, examples demonstrate how this refined joinery system upheld heavyweight timber architectures for centuries through mastery of grain-contravening connections.