Oklahoma’s News 9 said a recent inspection of the roof found “extensive deterioration” that had been unknown.

Other options were reportedly considered, but copper was chosen as the way to move forward due to its expected lifespan of about 60 years, Project Manager Lynnsee Boyse told the station.

According to the official Oklahoma Capitol Restoration website, the building was constructed between 1914 and 1917.

“But in 2014, after a century of heavy use, harsh Oklahoma weather and inconsistent maintenance and preservation efforts, the building’s mechanical systems were failing, the exterior façade was crumbling and its prospects of meeting the state’s needs for another hundred years were fading,” the website says.

Subsequently, lawmakers enacted legislation to provide funding via a $120 million bond for the capitol building’s top-to-bottom restoration. Another bond was issued for $125 million in 2016.

Sources say a set number of dollars was earmarked as contingency funding, meaning officials will be able to cover the cost of the unexpected roof replacement without having to find additional monies.

Construction began in 2015. The primary contractor is Manhattan Construction.