Largest proportional increase in cost for a building project

The initial cost was estimated at AUS $7 million, but by the end of the construction process in 1973 the Sydney Opera House had cost AUS $102 million to build. This represents a cost overrun of AUS $95 million – more than 14 times the first estimate. Today, the building’s much-loved white lines adorn the Sydney skyline, and countless tourist adverts for the country, but it remains the pre-eminent single example of a cost-planning disaster in modern accounting history. Danish economic geographer Bent Flyvbjerg studied 300 projects in 300 countries (including the Channel Tunnel, the Los Angeles subway and China's Three Gorges Dam) and found that the Sydney Opera House outstrips them all for cost increases. Since it was Bent Flyvbjerg's compatriot, Danish architect Jorn Utzon, who originally designed the building, perhaps there is a kind of poetic justice in the judgement.