The three damaged windows are not the first to break on U.S. Bank Stadium's 200,000-square-foot glass exterior. (Star Tribune/The Minnesota Star Tribune)

Three broken windows high on the southeast corner of U.S. Bank Stadium broke during the spring thaw and await replacement as winter comes knocking.

The three 5-by-8-foot panes are in the clerestory between the vertical wall and the roof, stadium spokeswoman Lisa Niess said — not the giant windows near the ground.

The windows broke when chunks of ice apparently struck a snow deflector on the building and bounced into the glass. She added that the southeast corner of the building has a unique design, with the snow deflector closer to the windows than in other areas.

Niess declined to provide a cost estimate for the new windows because the Minnesota Sports Facilities Authority (MSFA) is awaiting bids for replacements. Niess said the long replacement process is connected to the fact that the windows are customized.

These are not the first windows to break on U.S. Bank Stadium's 200,000-square-foot glass exterior.

On July 21, 2016, before the building's opening in August, a pane of glass on the north side of the building was broken by a pedestrian who threw a piece of decorative rock at the glass. That 10-by-5-foot window was double-paned so the breakage didn't expose the building's interior, but the broken glass was highly visible. Replacing the window took several weeks and left the building in less than perfect shape for the grand opening.

The expanses of glass are a signature design element at the stadium, but they've also become an issue because they're a fatal target for birds and sometimes let too much light into the building.

The glass had to be covered during the 2019 Final Four basketball tournament, requiring the purchase of multimillion-dollar custom curtains. And two weeks ago, a $300,000 bird mortality study concluded that an average of 111 migrating birds die from collisions with the glass annually. Stadium operators and the Vikings are considering strategies, including placing film on the glass, that would help the birds avoid harm.

The stadium's first troubling design problem had nothing to do with glass. The zinc panels that cover the exterior required reinforcement after some came loose in storms during summer 2016. During a winter storm in December 2016, a couple of panels flew off the building. After months of inspections and panel reinforcement, that problem appears to have been fixed.

Rochelle Olson • 612-673-1747