In 1998, workers constructing an industrial park on the outskirts of Fukushima, Japan, made one of the largest archaeological discoveries in the country’s modern history. The ruins at Miyahata, which date back to Japan’s Jōmon period (circa 12,000 B.C. to 300 B.C.), are among several recent major archaeological finds that have begun to shed light on Japan’s prehistoric civilization, a hunter-gatherer culture credited with making some of the world’s earliest ceramic pottery. (“Jōmon” is derived from the cord markings of the civilization's ornate pots.)
Japan’s first museum dedicated to this period opened on that site last year, about 15 years after the original design competition was held. The winners, Tokyo-based Furuichi & Associates with Suzuki Sekkei, designed the 12,400-square-foot museum as a two-story, concrete structure whose main entrance hall sits atop the excavated ruins, which are illuminated and on display courtesy of an expansive glass floor.
Mirroring the irregular terrain of the exposed ruins is a dramatic ceiling-scape made of jagged wood panels that recalls the cave dwellings first used by Jōmon societies. These communities later built villages of earthen pit-houses with timber frames, a detail that inspired Furuichi & Associates’ use of wood. The ceiling panels are structural, acting as truss-like members in a complex space frame and creating one of the first true wood-panel structures in Japan. “Even architects … ask me, ‘Is it just a ceiling?’ ” says Tetsuo Furuichi, the firm’s founding principal. “I say, ‘No, this is structure.’ Nobody thought it was structural. It looks like finishing only.”
The geometry of the wood panels derives from the pottery typical to the Jōmon culture. The architects abstracted the flared shape of a “flame pot” (named for its flame-like ornamentation) into a hexagonal pyramid, forming an inverted wooden cone that they repeat to create the tessellated structure, which supports a gable metal roof that floats above the 2,900-square-foot entrance hall.
Designing the panel structure was as complex as it looks. “We were very confused at first,” Furuichi says, “but with the help of the computer, we found some rules.” The architects used Vectorworks to create a structure from three unique types of cones, each of which is made up of six kite-shaped panels, but the digital model was still too abstract. “We couldn’t understand the actual space on the computer so we started making a [physical] model,” Furuichi says. “We made many models.”
However, the models weren’t enough to prove the design’s structural soundness to local government officials, who refused to issue a building permit until Masahiro Inayama, a well-known structural engineering professor at the University of Tokyo and timber expert who had collaborated on the museum’s final design, personally reassured the officials of its integrity. The museum’s future was also imperiled by the 2011 earthquake that destroyed the Fukushima Daiichi Nuclear Power Plant, just 40 miles to the southwest. Before construction began in 2013, the museum’s site was stripped of its soil and tested for radiation.
Once the design was approved, it took three months to build the wood roof structure. Comprising pine-glulam top and bottom chords, offset by approximately 9 feet, the base truss ties into the museum’s primary concrete structure via two wide-flange steel beams that top the walls flanking the entrance hall. The lower chords consist of two 14-inch-wide, 4.7-inch-deep beams attached with mitered joints. The upper chords comprise two adjacent 12-inch-wide, 6-inch-deep beams with angled notches through which the pyramids’ apices pop. The chords are concealed from visitors below, preserving the crystalline effect of the repeating cone shapes, which are roughly 8 feet tall and 9 feet in diameter.
Each panel is made from 1.2-inch-thick medium-density fiberboard and ranges between 6 and 12 feet long, and between 4 and 9 feet wide. Fabricated 20 miles from the site, the panels are glued together and screwed into perimeter 2x4s. Like the lower chords, the panels’ edges are mitered to make the joints appear seamless, though many of the angles were adjusted on site by the general contractor, Ando-Gumi, which has experience working on Japan’s historic shrines and temples. Anyone who does such work “has a very good hand,” Furuichi says.
Where the ceiling cantilevers outside the museum’s exterior wall, the structural wood panels were painted with a transparent finish coating (Telios Coat, by Nikko) to protect the wood from moisture and humidity. Inside, the panels are finished in 5-millimeter-thick sheets of high-quality, flame-retardant plywood veneer. Furuichi wanted to leave structural panels exposed, in a nod to the rough timbers used in Jōmon pit-houses. Building codes required a fire barrier, however, making the plywood a necessity. “I’m a little bit disappointed,” Furuichi says half-jokingly. “This wood structure is too beautiful.”