3D model: Kanawa-tsugi by thejoinery on Sketchfab
Assembly insights
Kanawa Tsugi traces its roots to Heian-period temple complexes. The joint's interlocking geometry distributes loads across shoulders while the metal hoop prevents separation during earthquakes. Miyadaiku rely on it for lengthening roof beams and repairing rotted posts where a simple scarf would fail under bending. The name refers to the iron ring (kanawa) that cinches the scarf together after assembly, a detail that distinguishes this joint from glue-only scarfs like Kiritsuke Tsugi.
Historical context
Kanawa Tsugi developed as carpenters sought mechanically locked scarfs for temple and shrine work. The metal collar became standard because wooden keys alone could work loose over decades of seasonal movement. The joint appears in major restoration projects across Japan and is closely associated with Ne Tsugi post repairs, where identical geometry on both halves allows a splice to slide together in confined spaces beneath a loaded structure.
Construction steps
- Establish a centerline on both timbers; lay out the stepped shoulders and angled scarf faces using a story stick.
- Saw the primary scarf angles on each member, then chisel the stepped profile and stub tenons.
- Cut the mating half to match; test-fit until the shoulders seat without gaps.
- Slide the two halves together lengthwise; drive draw pins (komisen) or keys if the design requires them.
- Install the iron kanawa ring around the joint and tighten to prevent separation under load.
Where to see this joint in Japan
- Todai-ji Temple — Nara — massive timber framework
- Kiyomizu-dera — Kyoto — stage and roof construction
- Edo-Tokyo Open Air Museum — Tokyo — restored historic buildings with post repairs
Variations
Some versions omit the metal ring when the joint is fully housed and pegged, but temple work typically retains the kanawa for seismic safety. Stub tenons may be visible or hidden depending on the repair context. For Ne Tsugi applications, the geometry is often simplified on the lower half to fit within a post splice.
Applications
- Temple roof beams
- Bridge restoration
- Heritage carpentry
Tools required
- Ryoba saw
- Nomi chisel set
- Dozuki saw
- Kanna plane
Related resources
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Ne-tsugi: Using Japanese Joinery to Repair Rotted Posts
A detailed case study of using kanawa-tsugi for ne-tsugi repairs on 100+ year old structures.