Obayashi Corporation built a pure wooden high-rise building in Yokohama City.
■ High cost is the current issue
Based on LVL (laminated veneer lumber), a general-purpose building material, the company has developed a building material that meets the fire resistance standard of two hours or more required for high-rise buildings by the Building Standards Law. This was used for the pillars and beams, and cleared the earthquake resistance standards. Avoid welding and bolting and use CLT (cross laminated timber) for walls and floors. Obayashi believes that this will eliminate the need for "curing" the concrete, leading to a reduction in the burden on the site and labor savings.
Mr. Mitsutoshi Nakamura of the wooden construction project team reveals that the cost is 30% to 40% higher than a steel frame construction of the same size, but client companies continue to receive inquiries about wooden construction. Many companies consider it as a building that shows their stance toward decarbonization.
■ "Hybrid" is also an option
In consideration of cost and fire resistance, the "hybrid construction method" with steel frame construction and reinforced concrete construction is also progressing. Takenaka Corporation and Mitsui Fudosan are planning a 17-story building with a hybrid structure of wood and steel in Nihonbashi, Tokyo. Hiroyuki Matsuzaki, who is in charge of wooden construction and wooden construction, said, "Three hours of fire resistance, which can be applied to all high-rise buildings, is scheduled to be realized by the end of fiscal 2022." The plan is to use wood for 20-30% of structural members, such as laminated wood that has been developed in-house to achieve fire resistance of 2 hours, and to limit the cost increase to 10-15% compared to reinforced concrete construction.
The hotel that opened in Sapporo uses a lot of timber from Hokkaido.
Mitsubishi Estate opened a hybrid wooden high-rise hotel "The Royal Park Canvas Sapporo Odori Park" in Sapporo city in October 2021. With 11 floors above ground, the 1st to 7th floors are made of reinforced concrete, the 8th floor is hybrid, and the 9th to 11th floors are made of pure wood. Using Sakhalin firs and Japanese larch from Hokkaido, they are appealing "local production for local consumption".
■ A limited manufacturer of building materials
Sumitomo Forestry has set up the "W350 Plan" to build a skyscraper wooden building with a height of 350 meters in 2041, and is first developing it overseas. In Melbourne, Australia, we are collaborating with NTT Urban Development to construct a 15-story hybrid wooden building.
Structural materials with high fire resistance are indispensable for the spread of wooden skyscrapers. However, there are only a limited number of building material manufacturers that can produce LVL and CLT materials. According to timber statistics from the Ministry of Agriculture, Forestry and Fisheries, as of 2021, there are 15 domestic LVL factories and 11 CLT factories. Considering technical hurdles such as compliance with fire resistance standards, there is a limit to the supply capacity.
Even so, forestry companies and building material manufacturers anticipate future demand for wooden high-rise buildings, and have started working to establish a supply system for the necessary building materials. Sumitomo Forestry plans to set up three or four timber complexes across the country that can produce multiple timber products such as plywood and chips from logs.
A total of 20 billion yen will be invested by 2024, and a biomass power plant will be installed alongside it to use energy. It has acquired 88,000 square meters of land in Shibushi City, Kagoshima Prefecture, and will start operations in 2025. President Toshiro Mitsuyoshi said, ``The weaker yen has made it harder to buy lumber produced overseas, and our competitiveness has declined,'' emphasizing the need to increase the supply capacity of domestic lumber. By 2030, the company plans to establish a system capable of processing 1 million cubic meters of logs per year.
■ Local companies establish a system
Local building materials manufacturers are also rushing to develop technology and establish bases. Shelter (Yamagata City), which deals with wooden construction, has independently developed wooden fireproof members, and has obtained ministerial certification for 3-hour fire resistance that can be used for buildings of all heights.
Meiken Kogyo Co., Ltd. (Maniwa City, Okayama Prefecture), a major CLT manufacturer, plans to start construction of a distribution center equipped with a large warehouse next to its manufacturing base within 2023. In 2021, it spent about 700 million yen to put into operation a production line for laminated lumber used for pillars and beams. Utilizing the new distribution center, we aim to create a system that can deliver large lumber 1.5m square and 14m long in as little as 10 days.
Meiken Kogyo's CLT plant (Maniwa City, Okayama Prefecture), which is planning a large increase in production
Chugoku Lumber Co., Ltd. (Kure City, Hiroshima Prefecture) also plans to expand its factory site after 2023 and increase its production capacity for building materials for buildings. The investment amount is expected to be around 20 billion yen.
In some cases, developers and general contractors have moved to manufacture or directly procure building materials. In June 2010, joint ventures such as Mitsubishi Estate, Takenaka Corporation, and Matsuo Construction (Saga City) began full-scale operations at a wood processing facility that manufactures CLT in addition to building materials for housing.
Mitsui Fudosan plans to use timber from approximately 50 million square meters of forests it owns in Hokkaido and elsewhere for the construction of office buildings, condominiums and other buildings. Takenaka Corporation has contracts with multiple forest owners such as Mitsui & Co. to procure timber.
The larger the building, the larger the building material. Wood processing machine manufacturers are rushing to prepare new models that can handle large cross-sections. Germany's Hundeger has started selling a model in Japan with a maximum cross section that has been expanded from the conventional 300mm x 1300mm to 610mm x 1300mm. Miyagawa Koki (Toyohashi City, Aichi Prefecture), a major domestic company, has released a model that can handle large cross-sections of 450 mm x 1250 mm, and has delivered three units.
■ Wide-ranging collaboration between the public and private sectors
According to the Forestry Agency, 13.9% of the public buildings that started construction in fiscal 2020 were wooden, and about 30% were low-rise buildings. However, looking at buildings as a whole, including corporate buildings, most medium- and high-rise buildings with four or more floors, both residential and non-residential, that began construction in 2020 are non-wooden. Hiroaki Kojima, Director of the Forestry Agency's Timber Utilization Division, said, "There is potential for timber to spread, especially in mid-to-high-rise buildings and non-residential buildings."
In August, Tokio Marine Holdings announced that it would build a new head office building with a hybrid structure, such as a wooden one. The amount of wood used is one of the largest in the world, and plans for wooden skyscrapers are expanding further. In order to further promote the use of wood, it is necessary to increase the supply capacity of building materials, reduce construction costs, and improve earthquake resistance and fire resistance. General contractors, building material manufacturers, and the government are required to work together to solve problems in the sense of supporting the forestry industry.
