9-5 Exploring the Potential of Materials — Nakanoshima Dai Building and Mokuzai Kaikan—

Materials possess a mysterious power to define “culture.” In Europe, stone has been used in architecture since ancient times, and “immutability” was synonymous with “permanence.”In Japan, where trees thrive in the monsoon evergreen broad-leaved forest zone, an abundance of timber has been used in architecture, and—as seen in the periodic relocation of the Ise Grand Shrine and the restoration and preservation of Horyu-ji Temple—"constant change" has come to represent "permanence."Although natural disasters such as earthquakes play a role, even in modern Japan, buildings less than 50 years old are being replaced one after another, undergoing constant change. Setting aside the question of whether this is good or bad, we may well find ourselves living within a “culture of constant change.”
The two projects introduced here are examples that thoroughly explored the potential of materials and opened up new possibilities for architecture. There is something about the power of materials that, for some reason, captures the heart.

The architect of the Nakanoshima Dai Building believed that, because the site is adjacent to a historically significant structure, the building should be a deeply sculpted skyscraper with rich shadows. Typically, shadow-casting louvers made of precast concrete are attached to the exterior of steel columns.However, for this project, large components were manufactured in a factory by embedding steel frames inside vertical concrete formwork, and these finished steel-reinforced components were then assembled on-site like LEGO blocks.
These precast concrete (PC) elements are commonly referred to as “precast concrete”; the Nakanoshima Dai Building was the first in Japan to utilize the steel-reinforced PC construction method to build a 35-story skyscraper, marking a groundbreaking achievement.Thanks to this design, the office spaces feature no steel columns around the windows, resulting in a clean, user-friendly, and open atmosphere. At the same time, the Nakanoshima Dai Building stands as a dignified office building rich in light and shadow, set within a historic environment.
The precast reinforced concrete components, manufactured in a factory, are designed so that the 3-centimeter-thick granite serving as the exterior finish becomes an integral part of the concrete. The structural columns, the stone cladding, and the deep-grooved vertical louvers—which help reduce energy consumption—were realized not as separate elements, but as a single, unified whole.Furthermore, special care was taken with the joints assembled on-site, and the realization of this building owes a great deal to the tremendous efforts of the people who manufactured the precast concrete (PC) components and the construction company that assembled them.

In traditional Japanese timber architecture, special techniques known as “shikuchi” are used at the joints of wooden members; similarly, the joints in the PC construction method incorporate special techniques, suggesting that the PC construction method shares certain characteristics with traditional Japanese timber architecture.On the other hand, in the sense of stacking materials, it also shares similarities with stone construction. This combination of characteristics from both wood and stone construction is what gives the PC construction method its unique charm.

Since ancient times, Japanese architecture has been rooted in a culture of wood. However, in modern times, simplistic assumptions—such as “cutting down trees robs us of greenery” or “wood is flammable”—have hindered the widespread adoption of architecture that embodies the charm of wood. Mokuzai Kaikan Over 1,000 cubic meters of lumber were used in this project; this is equivalent to sequestering more than 600 metric tons of CO₂ in the heart of the city, and new saplings are being planted in the satoyama forests where the trees were harvested. The production cycle of timber—which coexists with nature—can, in fact, be sustained through the use of domestically sourced wood.

It is true that the Building Standards Act imposes regulations on the use of wood in buildings in downtown areas. These regulations pertain to the use of combustible materials and fire-resistant construction.At this location (Mokuzai Kaikan), the top floor features a hall with a wooden structure, and for the exteriors and interiors of the standard floors, standard-grade domestic lumber—which is widely available on the market and easily accessible to anyone—is used throughout, without any non-combustible treatment using chemicals or other agents.By employing various ingenious solutions to address general legal regulations, we were able to realize a seven-story office building that showcases the appeal of wood in the city center. These solutions included ensuring that the hall’s wooden structure met the criteria for Ministerial Certification from the Ministry of Land, Infrastructure, Transport and Tourism to verify its fire resistance, and securing an exemption from interior design restrictions through the Evacuation Safety Verification Method.

Mokuzai Kaikan The windows face west, a direction generally avoided. However, the deep terrace on this west-facing side—constructed using wood—not only blocks the sun but has also become a place for office workers to rest and socialize.Furthermore, in the hall on the top floor, solid wood was used in a traditional construction method—including joints such as the “chase-and-plug” technique—to create a striking, expansive wooden space. Thanks to these appealing features, Mokuzai Kaikan garnered significant attention as an example of urban architecture that makes use of wood.

In Japan, trees planted after the war are now reaching maturity, but demand for domestic timber remains sluggish due to price competition with imported wood. I hope that the techniques and innovations employed in “Mokuzai Kaikan” will serve as a prototype demonstrating that wood can be effectively utilized in urban architecture.

(References)
(2009) *Detail*, October 2009 issue, Shokokusha
(2009) *Nikkei Architecture*, September 14, 2009 issue, Nikkei BP
(2010) *Architectural Technology No. 720*, Architectural Technology