The figures are the latest attempt to put a price tag on keeping the aging downtown government building in service as the council debates whether to invest in the repairs or leave and redevelop the property.
The projections are lower than those made earlier by other consultants, including engineering firm AECOM, that put the cost of repairing, modernizing and operating City Hall at more than $1 billion over 20 years.
The latets estimates focus on major repairs over roughly six to 10 years rather than the building’s total long-term costs.
One consulting team, Gresham Smith, estimated repairs would cost $531.6 million if completed over roughly six years or $556.8 million if spread over 10 years. A second consultant, WM2 Company, estimated costs ranging from $591.2 million to $610.8 million.
The proposed work includes repairs to the roof, elevators, plumbing, electrical systems, generators and other major building components.
Consultants also cautioned that hidden problems, including water damage, asbestos or deteriorated pipes, could push costs higher once construction begins.
This is a developing story that will be updated.