Fitting wooden joints together like complex puzzle pieces, tsugite is a traditional Japanese technique struggling in the face of ever-tightening regulations, but modern architects are refusing to let it be forgotten.
Held together without glue, nails or metal supports — the works of tsugite craftsmen have been a staple of traditional Japanese design for centuries. The most common joint mechanism during the 12th to19th century, it employs both satisfyingly simple and fantastically complex cuts in timber, interlocking to create surprisingly strong bonds.
Referring to the joining of two pieces of wood, also known as a splicing joint, tsugite is often used in conjunction with shiguchi — an angle joint using similar techniques. There are three primary arrangements for the former:
The relation to the supporting beam is also crucial — known as shintsugi when set squarely atop a pillar and mochidashitsugi for when the joint is extended beyond the supportive pillar — offering less strength overall. The shapes of the cuts themselves range in intricacy and have hundreds of variations, with 48 outlined in the well-respected guide The Art of Japanese Joinery, by Kiyosi Seike.
Used in both traditional homes and shrine building, the hand-made cuts are a skill honed over decades and passed on through generations. Unfortunately, the strict earthquake regulations mean that it is struggling as modern materials and new inventions offer safer alternatives.
While the future of such a traditional technique could appear bleak, there are teams around the country working hard to develop techniques that can prevent its loss. The use of CNC woodworking machinery like that made by Marunaka in Japan enables companies to use the joints for large-scale projects as they can be made faster and more affordably, albeit while sacrificing the craftsman's touch.
At the Kyoto University Research Institute for Sustainable Humanosphere (RISH), Akihisa Kitamori spends his days testing the strength of tsugite joints by applying pressure to joints that are replicas of shrines or new designs. Keen to maintain the tradition due to the sustainable nature of wood, the abundant supply in Japan and the warmth only a hand-crafted home can bring — the team works to develop new techniques and test out their developments.
Through their own research and experimentation as well as the studying of disasters and their impact on local structures, they have made headway in revitalisation of the skill. While larger buildings like shrines often survived earthquakes, small homes using the same designs would not, and they have highlighted the importance of maintenance as well as dimensions in the strength of the joints. Unfortunately, traditional earth walls common is older buildings are given the lowest strength score when assessed for seismic strength, as the wooden beams used for internal frames shrink over time. The gaps left in joints mean even small quakes can lead to movement in the wall, and as they now encase fittings like windows and pipes, the damage can be extensive. To counteract this the lab is working on compressed wood which swells over time due to condensation, filling any gaps that develop.
Despite these issues, tsugite is still being utilised in modern designs across Japan and further afield, pioneered by Japanese architects. While it can be difficult to use tsugite alone for structures given the risks, it can be combined with reinforced supports or used as decorative additions to new buildings.
The modern possibilities for tsugite are displayed rather fittingly at the headquarters of the Association of Wood Wholesalers in Tokyo. Designed by architectural firm Nikken Sekkei, the building uses a reinforced concrete frame for structural support and an eye-catching cedar-frame facade. Individual engawa spaces are were created to allow cool air to flow through the building while avoiding sunlight, incorporating another traditional Japanese element into the building. The company opted for the most common off-the-shelf pieces of timber: 115mm x 115mm pieces of Japanese cypress, demonstrating the possibilities of Japanese wood. Tsugite joints were used to create horizontal stretches of up to 30m, although the vertical lengths required additional steel bolts and oak plugs to ensure structural load bearing was maintained at a safe level. By combining traditional techniques with modern reinforcements, the building demonstrates that the future of traditional skills is far from over.
One of the leaders in this field, Kengo Kuma left Tokyo for a number of years during his career to learn from and work alongside traditional craftsmen in Japan's Countryside. Today, he creates buildings with a focus on sustainability and natural materials, favouring Japanese wood above all. A prime example is the Yusuhara Wooden Bridge Museum in Kochi prefecture, which joins two buildings, 47m apart. Surrounded by forests and passing across a local road, the bridge is made of interlocking beams of local cedar, varnished but left unpainted. Shorter beams are layered, supporting increasingly longer ones placed above them, tapering to a central point supported with a steel-cored column. As in the traditional style, the wooden joints are all exposed, offering a glimpse into the intricacy of the skilled construction.
The Prostho Museum Research Center was inspired by a traditional Japanese toy called chidori, an entirely wooden contraption which can be extended by twisting the various joints. The toy is linked to Hida Takayama in Gifu prefecture, where skilled craftsmen still remain. Working alongside structural engineer Jun Sato, Kuma was able to take the traditional toy's structure and enlarge it safely, to create a building. Allowing plenty of natural light to flood in as well as creating a bird's nest like style, it is a fascinating example of the wonders of wood and natural joinery in modern architecture. Similarly, the Sunny Hills Japan project in Omotesando has a forest-like structure created from traditional joints - a stark contrast to the contemporary buildings of the up-market area.
There are numerous examples found throughout his modern creations either employing tsugite for the complete structure or as a decorative element. The famous Dazaifutenmangu Omotesando Starbucks in Fukuoka, for example - brings together old and new, while pavilions like Yure in France and Kodama in Italy both introduce the skills abroad. One prime example of a modern building emplying the traditional techniques is the Tamedia Office building in Switzerland, designed by Shigeru Ban Architects. Freed from the strict earthquake regulations of Japan, they were able to create a structure entirely made of wood, using giant pin-joints for the Zurich building. The natural sources comply with the country's extensive energy rules and the use of an air-recycling system for temperature regulation between office and public spaces. Leaving all joints entirely visible, the tsugite influence is clear, albeit with a modern twist.
While the traditional technique cannot return to its former ubiquity in every-day buildings, there is hope for it yet. By utilising strengthened support systems and embracing modern styles, tsugite can remain a Japanese tradition at the forefront of architectural design.