Sydney Opera House Roof

The Sydney Opera House in Sydney, Australia, is famous above all for its roof: groups of nested white "shells" or "sails" covering two main performance halls and a restaurant. Designed by Danish architect Jørn Utzon, who won an international competition in 1957, it opened on 20 October 1973 and was inscribed on the UNESCO World Heritage List in 2007.

The geometry problem

Utzon's competition design showed curved shells whose geometry still had to be worked out before they could be built. The structural engineers were Ove Arup & Partners. In mid-1961 the team adopted the spherical solution: every shell surface would be cut from the same sphere, with a radius of 75.2 m (247 ft). Because all the curves were the same, the shells could be made from repeated, prefabricated parts. Who first proposed the idea is disputed.

Structure

Strictly speaking, the roofs are not thin shells. They are made of precast concrete ribs supporting precast concrete panels. The builders, Hornibrook, made about 2,400 ribs and 4,000 roof panels on site, and the roof comprises 2,194 precast sections weighing up to 15 tonnes each. The highest point is about 67 m (220 ft) above sea level.

The tiles

The shells are clad in 1,056,006 tiles made by the Swedish firm Höganäs AB, which normally made stoneware tiles for the paper-mill industry. The "Sydney tile", 120 mm (4.7 in) square and made of clay with a small proportion of crushed stone, took three years to develop. Tiles come in two finishes, glossy white and matte cream, laid in a subtle chevron pattern.

Construction stages

• Stage I (1957-1959): planning; site work began in March 1959.
• Stage II (1959-1963): podium.
• Stage III (1963-1967): outer shells.
• Stage IV (1967-1973): interiors.

Utzon left the project on 28 February 1966 after disputes with the New South Wales government and never returned to Australia. The final cost was about A$102 million.

Significance

The roof made the building one of the world's most recognisable structures and a landmark in the use of prefabrication to build a complex curved roof.