Mortise-and-tenon joinery for modern timber construction: Quantifying the embodied carbon of an alternative structural connection

The mass timber industry offers a compelling pathway for low-carbon structural systems in buildings, replacing carbon-intensive materials like concrete and steel with sustainably forested wood. However, conventional structural connections in mass timber construction are largely made of metallic materials, such as screws, nails, and plates. In contrast, joinery, or geometrically interlocking all-timber connections, is globally prevalent in historic timber construction. This paper investigates the potential of applying joinery, specifically the “Nuki” mortise-and-tenon joinery connection, to contemporary mass timber construction from perspectives of structural behavior and carbon savings. Considering single spans supporting one-way cross-laminated timber (CLT) floor systems at the mid-rise residential scale, carbon savings ranging from 7 to 40% are possible at the beam-joint scale by using Nuki joints instead of steel concealed beam hangers, a more conventional mass timber connection. While these savings are smaller at the building scale, the paper nevertheless demonstrates a methodology and results for quantitatively comparing the scale of savings achieved by implementing this historic but contemporarily alternative connection type.