The Superstack was built by Inco Limited (and later purchased by Vale) at an estimated cost of 25 million dollars. Construction on the structure was underway during the Sudbury tornado of August 20, 1970; the structure swayed heavily in the wind, but remained standing and suffered only minor damage. Six workers were on top of the construction platform when the storm hit, and all survived. The same day was the final day of construction on the stack, with the construction fully completed by the evening of August 21.