When seeking design inspiration for a chapel at a resort hotel in Nagasaki, Japan, Momoeda Yu Architecture Office (MYAO) looked to the nearby Ōura Tenshudo, a wooden, Gothic-style Catholic basilica that French missionaries built in 1864. The firm’s namesake founder, an alumnus of Kengo Kuma and Associates, wanted to explore wood construction while also paying homage to the basilica, the rare tourist attraction that is also beloved by locals.
The one-room, 60-seat Agri Chapel is almost a cube, approximately 30 feet in length, width, and height with expansive floor-to-ceiling windows. Once inside, visitors are greeted by an array of stacked tree-like pillars that rise the height of the chapel, filling the volume. Inspired by fractal geometries, the interconnected cedar structure supports the chapel’s flat roof. With no altar and the interiors finished in white, the wood structure becomes a sculptural centerpiece, drawing the eye upward and encouraging contemplation, much like the vaulted ceilings of Gothic cathedrals.
Momoeda first conceived the branching structural system while studying at Yokohama National University in Kanagawa Prefecture. The system divides the chapel interior vertically into three tiers, again similar to Gothic architecture. With each tier, the trunk-like pillars multiply in number—first four, then eight, then 16—while shrinking in size by a factor equal to the square root of two. At grade, wood members are 4.7 inches square; at the next level, 3.5 inches; at the final level, 2.3 inches. At each tier, the pillars bundle five cedar posts, which support up to eight angled beams that splay like branches. These boughs either intersect with those of the neighboring trees to support the next tier of pillars, or terminate in space, tying into the base of the overhead tier of trunks via steel tension rods painted white. These latter, truncated beams are anything but superfluous, Momoeda says. “Without these beams, the building would collapse.”
It’s common for Japanese architects to make “a lot of models,” Momoeda says, and he is no exception. He and his team built dozens of digital and plastic models, exploring the relationship between each layer of trees and their impact on the space. Quickly, they realized that simply doubling the number of trees at each tier would clutter the chapel by the second round: The architecture would have no room to breathe.
To solve this problem, the designers twisted the trees 45 degrees between tiers, partially embedding several trees in the middle tier as vertical supports for the exterior walls. That is, the second tier consists of four stand-alone pillars and eight additional half-pillars. These latter trunks, which carry half the structural load of a stand-alone trunk, help support the second set of angled beams that supports the top tier of 16 trees, which stand apart from the walls.
The unique condition of the half-embedded trunk structures in the middle tier was one of the project’s more challenging aspects, says Momoeda, who worked with Jun Sato Structural Engineers out of Tokyo. The team designed a custom gusset plate to which they could attach both the angled beams and three 0.63-inch-diameter steel tension rods. A centered angled knife plate, matching the depth of the beams, connects each beam to the columns via a concealed steel plate. “This detail was complicated,” Momoeda says.
The other steel connections were no less so. Where the angled beams form the base of an upper pillar—which, again, are rotated 45 degrees between tiers—a steel base plate anchors a rectangular steel sleeve that supports the five-post trunk as well as six tension rods. Four posts attach to each face of a central post, which slips inside the sleeve and is secured with steel bolts. Where the trunk meets its crowning bough, a steel node with angled knife plates works in combination with mortise-and-tenon joints, fitting the maximum eight branches together like puzzle pieces.
Each of these details was fabricated in plastic by MYAO and shown to local contractor Yushin Construction before they were built and shipped to the site. Momoeda specified cedar because it is readily available, and thus economical, and milled outside of Nagasaki. Cedar is also commonly used in traditional Japanese houses, which helped the novel structure feel familiar. Construction took four months with a team of four carpenters. The exterior walls were erected first and then the tree-like pillars built from the bottom up.
It’s an understatement to say that the Agri Chapel is a personal project for Momoeda. “This building is in my hometown,” he says. “My parents and my family can see it.” The chapel is also his firm’s first built project. Since its completion in late 2016, it has captured the attention of the public as well as that of the profession. Architects travel from around Japan to Nagasaki to visit the chapel. “It’s quite far from Tokyo, but many people come,” Momoeda says. “So I’m happy.”
