Reedfall | ヨシ天井

“Reedfall” is a self-supporting reed ceiling installed in the atrium of a former sake brewery located in the historic castle town of Omihachiman-City. The building, originally composed of multiple earthen-walled storehouses, has been intricately merged through successive renovations. This ceiling takes advantage of the lightweight nature of reed and the structural stiffness derived from its tubular cross-section, forming a truss-based, self-supporting design.

Steel bars spanning both sides of the atrium served as temporary guides during construction, with the reed elements assembled and fixed into trusses along those guides. The overall arrangement of the reeds was inspired by the image of a waterfall: on one side, they are placed in a somewhat irregular and randomized orientation, while on the other, they are aligned to evoke the smooth downward flow of falling water. The design responds not only to the vertical openness of the atrium, but also to the visual and spatial connection with the adjacent room.
Although safety ropes are installed above the ceiling as a fail-safe precaution, the structure stands entirely on its own once assembled. Each structural plane spanning the atrium is isolated to prevent the formation of large, heavy masses. Even in the unlikely event of a collapse, the design ensures that potential damage to occupants is minimized.

Design and construction: Takuo Nagai Lab + Volunteer students from the University of Shiga Prefecture
Program: Interior design (Ceiling)
Year of completion: 2018

近江八幡の旧城下町，土蔵が増改築により複雑に一体化した旧酒造所の内部にある吹抜け部に設置されている。ヨシ天井は，ヨシの軽量さとパイプ状の断面を持つため剛性が高いという特徴を活かした軽量自立天井である。制作のガイドとなる鉄筋を吹抜けの両側にわたし，ヨシでトラスを組みながら固定している。ヨシの配置は，滝をイメージし，一端はややランダムに方向を不揃いに，他端は滝の流れを表すように，ある程度方向を揃えている。吹抜けの空間の広がりや，隣室へのつながりを意識した意匠である。
天井の上部にはフェイルセーフのための吊縄を一応設けてはいるが，組み立て後はヨシのみで自立する構造である。さらに，スパン方向の構面ごとに縁切り，万一，人の頭上に落下しても，大きな重量の塊となることを避け，被害を最小限に抑えられるよう配慮した。

設計・施工：永井拓生研究室＋滋賀県立大学学生有志
用途：内装（天井）
完成年：2018年