EXPO 2025 Osaka Grand Roof Ring

The iconic wooden ring structure built for the 2025 Osaka World Exposition on the artificial island of Yumeshima. With an inner diameter of approx. 615 m and a circumference of about 2 km, it was certified as the world's largest wooden structure by Guinness World Records in March 2025.

Use

Bridge

Area

Osaka (Yumeshima)

Completed

2024

Height

22 m

Architect

Sou Fujimoto (master designer) / Obayashi Corporation and partners

The World’s Largest Wooden Circle

On the artificial island of Yumeshima in Osaka’s Konohana Ward, the Grand Roof Ring (大屋根リング) took shape as the centrepiece of the 2025 World Exposition: a circular wooden building with an inner diameter of approximately 615 metres, a width of about 30 metres, a height ranging from roughly 12 to 22 metres, and a total circumference of around 2 kilometres. On 4 March 2025, it was officially recognised by Guinness World Records as the world’s largest wooden structure. The construction cost was approximately ¥34.4 billion. Architect Sou Fujimoto served as the master designer, while Obayashi Corporation and partner contractors handled the build.

Throughout the Expo’s run from 13 April to 13 October 2025, the ring served as both a grand gateway and a roofed promenade connecting the venue’s pavilions. Domestic Japanese timber — cedar and cypress among other species — was used extensively for the structural members, creating a warm, richly textured surface at an otherwise unprecedented scale.

Demonstrating the Limits of Timber

Constructing a circular building more than 600 metres across in timber, without relying on a steel skeleton, had no precedent in modern architecture. The project tested the supply chains and joinery techniques of Japan’s forestry and construction industries simultaneously, and its successful completion was widely read as a demonstration of how far Japanese timber-frame technology has advanced. The ring is visible from a considerable distance — from boats on Osaka Bay and from parks on the mainland — giving Yumeshima an entirely new silhouette on the horizon. Post-Expo discussions have included proposals to preserve a section of the ring as a permanent monument.

Summary

Completed in 2024, the Grand Roof Ring has an inner diameter of approximately 615 m, a height of 12–22 m, and a construction cost of around ¥34.4 billion. Certified by Guinness as the world’s largest wooden structure, it stands as one of the most ambitious applications of timber in the history of architecture. Whether it remains as a monument after the Expo or is eventually dismantled, the ring marks the moment Japan’s wood-building tradition took on a truly global scale.