Wood: Part 2​​​​​​​​​​​​​​

Residential Skeletal Frames

Timber’s many advantages in earthquake-rich environments made the skeletal timber frame system Japan’s traditional choice in residential architecture—a system characterized by only vertical and horizontal connections, and modular addition of rooms on the horizontal plane. Not only sturdy, lightweight and durable, but easy to assemble and insulate, these structures have been used with great success for centuries in minimizing earthquake damage and loss of life. Additionally, the many components and special joining techniques used in timber structural frames provide multiple load paths that absorb an earthquake's force and distribute its energy to help ensure the structural integrity of the residence. (See “Technical Construction Issues” and “Wooden Joints” below.)

The ready availability and diversity of high-quality species of timber found in most regions of Japan ensures skeleton frames with durable, earthquake-resistant load-bearing capabilities. These high-quality timbers are used in not only the structural framework, but interior spaces, roofing, verandas and other parts of the building. The most popular species for use in the frames are Japanese cedar, cypress, and pine, which are generally ready for harvest and use after just forty to sixty years of growth. Moreover, Japanese cedar and cypress are highly resistant to both mold and insects, which makes them particularly well suited to the Japanese climate. (Fig. 84)

Despite the current availability of new styles and building materials, most domestic builders remain loyal to skeletal frame construction. On the one hand, while Japanese architects are known for their integrated vision of culture, climate, and construction, and of course their remarkable technical skills and craftsmanship, the individual building techniques used in the frames themselves are relatively straightforward. On the other hand, these techniques, whose goal is living space in harmony with human needs and nature’s realities, are based not only on the deep knowledge, but perhaps on the even deeper love, of wood.

Technical Construction Issues

The traditional residential building process and techniques involve arranging Japanese cedar, cypress, pine, chestnut, and other lumber in optimal old-fashioned multi-angled joints (shiguchi) (Fig. 85) and straight joints where timbers are placed end to end to provide added length (tsugite) (Fig. 86). The wooden frame then goes on granite cornerstone pillars standing on stones instead of being fixed deep into the ground (ishibadate) (Fig. 87). Under this approach, carpenters follow the long-standing protocol of developing and designing the entire building plan, cutting the timber themselves, and then working together with teams of specialists to erect the structure.

Wood is a material whose unique strengths and physical properties realize their full potential in flexible structures. Through an intricate arrangement of joints, a flexible structure disperses stress across the entire assembly. The key components are joints that connect pillars at the top and provide resistance against lateral load (sashikamoi) (Fig. 88); horizontal ties that interconnect the bases of posts and provide resistance against lateral load (ashigatame) (Fig. 89); and beams that go through pillars, providing horizontal resistance and serving as the framework for the building’s walls (tõshinuki) (Fig. 90). For the angled joints linking the members of the structure, traditional Japanese techniques use a type of joined wooden frame for connecting members and an important component of the horizontal lattice structure (aikaki watariago) (Fig. 91). For the walls, builders plaster a course mud daub (tsuchikabe) over laths of bamboo woven into lattice-like arrangements (takekomai) (Fig. 92). To keep external forces from damaging the wooden structure, traditional methods focus on enabling it to respond flexibly to pressure brought to bear on the cornerstones by natural or other outside forces.

Traditional buildings use at least ten types of lumber with different thicknesses and shapes, depending on the magnitude, direction, and role of the load involved. The angled joints connecting all the different wood components thus have different orientations and shapes. The buildings also adopt a style which leaves most structural materials exposed, known as arawashi. Since the vast majority of structural components are readily accessible to visual inspection, carpenters must be extremely precise in how they cut and place the beams—which, in turn, means nearly all of the carpenter’s most intricate, demanding work takes place before the framework actually goes up.

Wooden Joints

While it is historical fact that guilds, protectionism, and political policies of the Togukawa shogunate restricted the use of metal fasteners in construction during the Edo period (1603-1868), the truth remains that metal fasteners cannot rival the longevity of all-wood joints unless installed in well-cured wood and protected from contact with air. In imperfectly cured wood, they can be loosened by seasonal shrinkage and expansion of the surrounding material, and when exposed to air are subject to rapid oxidation in Japan’s humid climate. Additionally, regular stress over time will result in metal fatigue. In contrast, all-wood joints gain strength as the wood ages and individual cells harden. Calculations based on the fact that wood typically grows stronger for two to three hundred years after being cut show that wood joints can exhibit greater structural integrity centuries after their initial fittings. This strength does gradually decline beyond that point in time, but only after about a thousand years will a properly cured timber beam return to its original strength when logged.

Mold

Much of Japan presents ideal growth conditions for mold and other fungi. Temperatures rarely drop below freezing or rise above 38°C year-round, and humidity can exceed seventy percent for weeks on end, particularly during the hot summer months. It is during the rainy season, however, that mold can truly thrive. Speaking from experience, Japanese women are quick to caution that even long hair may mildew if not properly dried, as well as lamenting the many shoes lost to mold during seasonal storage in shuttered closets.

Traditional wooden construction helped prevent mold by raising the ground floor of buildings above actual ground level in conjunction with porous walls that allowed air to flow freely throughout the entire home interior. Once the samurai came to power in the late twelfth century, interior air flow improved as residences were no longer cluttered with furniture or permanent fixtures, as specified in the Bushido Code of the Warrior.

Private homes were typically built with heavy timbers for excellent natural ventilation. Since Japan’s relative humidity can remain high even in winter, residents enjoyed unobstructed air flow even when home interiors were shut off from the outside—through spaces between wooden shutters and paper doors, between walls and roofs, and frequently through fully open smoke outlets. (Unfortunately, this natural ventilation made living conditions in these homes uncomfortably chilly in winter.) It was not until the mid-twentieth century that Western air quality specialists scientifically determined that moisture control and proper ventilation were critical to residents’ health—a feature traditional Japanese architects had built with pride into their work products for almost eight hundred years.

Timber and Joinery in Satsuma Residences

Below are examples of sugi and keyaki wood, as well as the various timber frame joints they are commonly used for.

Week 4: The Interview & the Temple

Hello, and welcome (back) to Japan Apprentice! The truth is, however, that at the end of another week with no word on a starting date to renovate my great-uncle’s cottage, I’m beginning to wonder if “apprentice” was the right word for the blog. And while I did find out that my uncle Koji applied for a grant from the town to renovate his late father’s cottage, which somehow makes the delay more understandable, that’s not exactly “progress.”

On the bright side, not having to work all day on the cottage freed up some time for other interesting activities. First, my conversation with Anne Kohtz, an American architect who lived and worked in Japan for twenty-five years. And second, my visit to a local Buddhist temple (Fig. 99) to compare its architecture to that of Hosshinji, which is four hundred years older and operates on a much larger budget.

Anne Kohtz and Studio Mikage 

There are more than a few foreign architects in Japan who have built careers working with the traditional indigenous architecture. Anne Kohtz is one of those. Ms. Kohtz received undergraduate degrees in political science and sculpture from the University of Oregon, after which she visited Japan, then returned to her alma mater for a master’s in architecture. Heading back to Japan, she subsequently found positions in well-respected architecture studios prior to launching her own shop, Studio Mikage, in 2020.

With much ground to cover and only thirty minutes to do it, Ms. Kohtz and I began our Zoom chat with Japanese architecture in general, quickly moving on to her specialty, which she described as “using natural materials to creatively blend traditional Japanese construction and design with modern, comfortable living.” One of my main takeaways was the shaku-sun system (Fig. 100), the traditional Japanese system of measurement used prior to the metric system. (One shaku is 10 / 33 of a meter, or 30.3 centimeters, and one sun is one-tenth of one shaku.) These and other standardized units of measurement allowed carpenters to plan room sizes prior to building construction with knowledge of the dimensions of just one wooden beam.

Based on her commitment to sustainability, Ms. Kohtz originally planned to concentrate her efforts on multi-family structures, but after extensive work with single-family homes and coming to fully appreciate the modular capabilities of Japanese houses, she shifted focus. Today, she prioritizes renovative work, restoring traditional homes in modern styles using traditional methods. I found her approach motivating and her dedication inspiring, no doubt because her goals dovetailed almost exactly with my own plans for an architecture career.

From goals we moved on to realities, in particular Japan’s abandoned housing crisis. Japan ranks number one in the world in such properties, with 8.5 million homes currently vacated—or one in seven of the country’s total residential units. The population has shrunk steadily since the late 20th century, producing progressively fewer children to fund social security and other safety nets for the burgeoning senior population in one of the world’s fastest graying societies. The majority of these homes are in rural areas like Satsuma (Fig. 101), although they are not uncommon in Tokyo and other urban centers. Together, Japan’s dwindling population crisis and expanding housing crisis represent existential social and economic threats that, up to now, the Japanese government has proven powerless to resolve.

For the past decade, my great uncle’s house was one of these vacant homes, “abandoned” by his death and that of his wife several years earlier. My memories of him, in particular, are just one of the many reasons for my impatience at the delays on getting underway with renovations. I believe that revitalizing communities should be the new focus of Japan’s housing industry—retrofitting vacant homes to create the appeal necessary to attract families to live in them. Ms. Kohtz emphasized that since traditional Japanese homes were built with wooden beams that could be disassembled and rebuilt, the renovations necessary to create comfortable modern homes should prove feasible at reasonable expense.

Shintokuji (Temple of New Virtue)

Shintokuji is Satsuma’s only Buddhist temple. Unlike Hosshinji, a large, established training temple with many monks in residence, Shintokuji is maintained by a lone head monk and his wife who minister to the needs of the community with funerals, as well as services to speed the souls of the recently deceased and more distant ancestors on their way to Nirvana. Given that Buddhism gradually assumed its own distinctive style of architecture after coming to Japan in the 6th century, it is no surprise that Shintokuji, founded in 1919, shares many architectural features with Hosshinji, opened in 1525, and other temples throughout Japan. (Shintokuji has no meditation hall or living quarters due to the absence of monks in training.) Buddhist architecture features high, coffered ceilings (Fig. 102) supported by large, cylindrical pillars (Fig. 103) with hand-carved decorative pieces (Fig. 104) between them. At the back of the main hall is a Buddha altar and, of course, the entire structure is assembled with traditional wood joinery.

As an aspiring architect, one of the items on display at Shintokuji that I found most interesting was a circa 1919 photograph of the newly raised skeletal timber frame not long before the structure was completed (Fig. 105). It showed a total of approximately one hundred people, with maybe two dozen standing on the roof support beams. I was impressed by not only the obvious strength of the frame, but the size of the workforce involved in erecting the structure in those days. It reminded me of the Amish barn-raising scene from the 1985 Harrison Ford film “Witness,” which I watched with my father when I was in high school.

In conclusion, even without the apprenticeship part of the trip so far due to renovation delays, it has been another educational week for me here in Satsuma. Even this far out in the country, there is no lack of new things to learn, including not only local customs but Kagoshima dialect. If my uncle’s grant doesn’t come through within a couple of days, my next destinations are the two local Shinto shrines and, if I can persuade my aunt to take me on her next day off, a cafe run out of a very old, traditional house, which I’ve been looking forward to exploring since I arrived. That said, I appreciate the kind feedback from friends and classmates, and will be working hard to get Week 5 out as soon as possible.