Nine months into the life of the $1.1 billion U.S. Bank Stadium, leaky walls and loose panels remain a concern without definitive agreement on the extent of the problem or the proper repairs, stadium officials said Friday.

Rick Evans, executive director of the Minnesota Sports Facilities Authority (MSFA), said the entire exterior of the building, which is covered in zinc panels, is being tested and studied by engineers and metallurgists. Evans, who's in his second month on the job, called the durability of the panels a health and safety concern that is "at the top of my priority list."

Panels have been a visible problem for almost a year. Passersby have seen repair work since last summer — even before the doors opened on the 66,200-seat building. Some panels flapped loose after summer storms.

Then in a December 2016 storm, a couple of panels broke from the building and flew off. Water is also a big issue.

In 2016, general contractor M.A. Mortenson paid several million dollars to replace a moisture barrier after dampness was found on a parapet — not a main indoor wall.

Now Mortenson is focused on the northwestern facade where water seeped into the building and created puddles in a women's restroom, a concourse and storage area.

Evans has a more encompassing concern about loose panels and leaks.

"Whether they're related or different is still a question in my mind," Evans said, adding that the problems on the northwestern corner create wider worries. "When we have an issue with one portion of the building, we're looking at the entire facade."

Mortenson, however, said the panel reinforcement was completed in March and the contractor is focused on the 27,500-square-foot northwestern face of the building, according to senior vice president John Wood. That's the site of the most significant water problems to date. Wood said the steeply sloped wall bears the brunt of the winds. The wall also doesn't get much sunlight so the insulation doesn't fully dry.

The proposed fix under consideration: replace moisture barriers on the joints of the building's interior panels, then add a new layer of Tyvek under the zinc panels for extra protection. Wood said Mortenson also will install "heat trace" to the lower edge of the wall to prevent icicles from forming.

Last winter, icicles had to be manually removed from the building so they didn't hit pedestrians below.

Neither Evans nor Wood would characterize the possible cost or range of repairs. But if the problem is big, the cost would be high and create a potentially major negotiation over who pays.

First, engineers and metallurgists, contractors and public officials need to reach agreement on the problem. Then they need to agree on the best solution and figure out who pays.

"I'm not focusing on the cost," Evans said. "I'm focusing on the cause and the solution."

Still Evans said he doesn't expect the MSFA to pay for any repairs.

Wood, however, said the addition of the Tyvek layer on the one wall would be the responsibility of the MSFA.

Despite the scope of the review of the exterior panels, Evans said, "it shouldn't be read to mean we've got horrible problems ... it's a complex fastening system and we're looking at all of it to make sure what we paid for is what we're getting."

The Minnesota Vikings, the building's main tenant, covered $600 million of the construction cost. Taxpayers were responsible for the other $498 million.

Problems weren't unexpected given the size and complexity of the building. The main concerns had been the roof, the pivoting glass doors on the building's western end, and the efficacy of the cooling system on bright, warm days. All those features worked smoothly.

"While we certainly wish it were perfect and wanted it to be perfect, we're going to fix it. Mortenson is going to shoulder its responsibility," Wood said.