It’s official. Osaka Kanasa’s “Grand Roof”—one of the world’s largest wooden structures ever constructed —is fully erected, with the 35 billion yen structure (or US $240 million) delivered one month ahead of schedule.
It comes as three of Japan’s largest contractors—which includes Obayashi Corp, now responsible for constructing Atlassian Central Tower, the world’s largest timber hybrid tower, Takenaka Corp, and Shimizu Corp—have been working around the clock to assemble the enormous timber ring, with attention now turning to the elevators, greenery, and eight internal pavilions.
Designed by Japanese architect Sou Fujimoto, the all-timber roof has a 2 km circumference, 20-metre height, and an 8-metre walkway; the 60,000 square metres “wooden ring” is the centrepiece of the “dream island.”
“The design is meant to evoke a sense of Unity in Diversity,” according to Mr Fujimoto, who said that the project is the centrepiece of the World Expo 2025 – the 170th anniversary of the first expo. He wanted “people to feel that this one sky is connecting all parts of the world, which is full of diversity as is shared by everyone,” adding that the design showcases “the future of wooden architecture to the world and Japan.”
“At 3.30 pm on Wednesday (August 21), the last piece of timber was put into place by crane, signalling the completion of the Ring one month ahead of schedule,” according to the Expo 2025 Osaka Kansai organisers.
Wood Central understands that the area beneath the roof will serve as a main promenade for the expo site, providing shelter from rain and sunlight during the event, which runs from April 13 to October 13 next year – with the rooftop of the ring will offer views of the surrounding pavilions of international participants.
Dream or reality? Concerns over Expo’s legacy
Dubbed “the most expensive parasol in the world,” the project has nonetheless been shrouded in controversy – with construction delays, surging material costs, and labour shortages resulting in Expo costs spiralling out of control (to more than US $1.5 billion).
After the Expo, the Grand Roof —which may or may not be partly recycled—was slated to become a resort island hosting Japan’s first casino—a project now expected to be delayed until at least 2030.
Wood Central understands that the Expo costs are shared by the Japanese national government, the Osaka prefecture, and the city and business communities. Osaka modelling shows that city residents will bear the heaviest tax burden—about US $125 per person.
The roof itself is supported by the traditional ‘nuke’ technique of joining horizontal beams and vertical pillars, which was also used for the famed wooden stage at Kiyomizudera temple in Kyoto.
Work is now starting on the surrounding pavilions
Now, attention is turning to the “Forest of Tranquility”, the eight Signature Pavilions, and hundreds of country-specific pavilions, most made out of Japanese wood, which will sit inside the giant wooden ring.
Last month, Wood Central spoke exclusively to Yuichi Shinohara, CEO and President of Shinohara Shoten, responsible for erecting the Austrian pavilion on site starting in February 2025.
Featuring an impressive musical score, Graf Holztechnik in Austria is crafting the 12-metre-high mass timber structure. Despite its delicate aesthetics, it is fully wind-resistant and boasts high performance.
“Strong winds are expected at the exposed location of the Expo site,” according to Alf Netek, project manager of the Expo office of the Austrian Economic Chamber, who said the installation will withstand wind speeds of up to 200 km/h—designed by Vienna architecture firm BWM, led by architect Johann Moser and Univ.-Prof. Peter Bauer from the structural engineering firm Werkraum.
Japan is one of the world’s largest consumers of timber – fueling a wave of new timber projects
As one of Japan’s largest timber fabricators – and one of the few to provide a one-stop-shop for mass timber construction from design, manufacturing and assembly, Mr Shinohara is at the forefront of the new mid-rise timber wave sweeping Japanese cities.
“We supply timber to more than 4,000 timber buildings every year,” Mr Shinohara told Wood Central, “with about 80% of that into the residential market and a (growing) 20% into the mass timber non-residential market.”
As it stands, Japan is the world’s fourth-largest importer of timber products, with the world’s third-largest economy importing more than 3,340,000 cubic metres of lumber last year.
“We are (now) a cheap country, with a proven record at delivering solutions at scale,” according to Mr Shinohara, who added that low prices for Japanese cypress (Hinoki) and Northern Japanese hemlock are helping to drive an uptake in domestic projects across the country.
It comes as Japan is now cutting millions of cypress trees, changing building standards, and investing in high-value timber production. The upshot is that the Japanese timber industry is booming, with the latest data from the Ministry of Agriculture Forestry and Fisheries of Japan pointing to a steady reduction in timber prices relative to other materials.
“The government is now putting a big emphasis on building out of Japanese domestic species,” Mr Shinohara said, a big change over the past decade. “In the past, concrete and steel were used for government buildings, but that has been turned on its head.”
As a result, Japan is now experimenting with a range of different timber systems, “including an 8-storey all-timber building, which did not use any steel or concrete,” Mr Shinohara told Wood Central, as well as “timber and concrete hybrid systems”, which opens up a new market in the low-rise, high volume construction.
