How Utzon Saved the Sydney Opera House With an Orange

In January 1957, the New South Wales government announced a 38-year-old Danish architect, Jørn Utzon, as the winner of an open competition for a new opera house on Sydney's Bennelong Point. Utzon's drawings showed a podium with white sail-like shells rising from it. The shapes were drawn freehand. They had no defined geometry, and the structural engineer, Ove Arup, could not figure out how to build them.

For four years Utzon and Arup's team tested parabolas, ellipsoids, and free-form shells. None worked. Each shell would have needed unique formwork, and the Australian construction industry could not pour curved concrete to that tolerance. Costs ballooned. Premier Joseph Cahill, who had pushed the project through, died in 1959 with the foundations still wrong-sized.

The break came in 1961. Utzon later described peeling an orange in his Hellebæk studio and seeing it: every sail could be a section cut from the surface of a single sphere, all 75.2 metres in radius. Identical curvature meant identical precast concrete ribs, mass-produced and assembled like a kit. Arup signed off. Construction restarted with a buildable geometry.

Utzon resigned in 1966 over a fight with the new state government about fees and interior design. He never returned to Australia, and never saw the building in person. It opened on October 20, 1973, ten years behind schedule and at A$14 million against an original A$7 million estimate. The sails are still spherical sections.