U.S. Bank Stadium soon may be encircled by a permanent security fence, replacing the chain-link fence that has surrounded most of the downtown Minneapolis structure since it opened in 2016.

The Minnesota Sports Facilities Authority on Thursday directed staffers to choose a firm to design the fence and landscaping. How much the fence will cost and who will pay for it has yet to be determined, although the stadium has a capital reserve fund for such expenses.

The Minnesota Vikings, the stadium's main tenant, long have been interested in permanent security fencing. And authority Chair Michael Vekich said the U.S. Department of Homeland Security has urged installation of permanent fencing to maintain the stadium's top safety ranking.

"They want us to move forward, and that's really the reasoning for doing it now," Vekich said.

Along with the potential retooling of club spaces and creation of a training area for event-day staff, the project would be the biggest planned renovation since the $1.1 billion facility opened its gigantic glass doors.

The original zinc siding on the exterior of the stadium was replaced because of water seepage, but the $21.5 million cost was covered by construction and design firms as part of a negotiated legal settlement. Blackout curtains for the 2019 NCAA Final Four tournament also cost millions.

Vikings vice president Lester Bagley said a permanent fence has been discussed since the stadium opened and that the sports authority's decision is a step toward understanding the scope and cost of the project. The Vikings pay millions in rent annually.

"Public safety has always been a priority for the Vikings. That means we constantly evaluate and improve security," Bagley said.

Vekich said the security project would be completed in two phases. First, the fence will be built around all but the stadium's west side, the building's main entrance outside the five large pivoting glass doors. Then a permanent structure will go up on the west side, where most of the magnetometers are.

It's too soon to say what the fence and new security perimeter will look like, but a demonstration photo showed an unobtrusive black version. Vekich said the public will have the same access to the area it does now and that the stadium won't look like a "fortress."

Authority board member Sharon Sayles Belton said she wants to make sure the fence doesn't look "industrial."

U.S. Bank Stadium had a couple notable security problems. In July 2016, days before the building opened, a pedestrian threw a rock and shattered a large exterior window pane on the stadium's north side.

During a Vikings game in 2017, activists entered the building, climbed a truss ladder, dropped from the ceiling and unfurled a banner protesting the Dakota Access oil pipeline. They dangled above the crowd in the east end zone later in the game but were arrested and faced charges.

The sports authority board on Thursday also authorized its staff to negotiate a contract with a bidder to examine the efficiency and design of interior club spaces, and to explore the possibility of building a break room and training center for event-day staff in one of the loading docks.

Sayles Belton asked why a dedicated training area was needed, given that the facility already has flexible spaces. "I'm just trying to figure out the cost-benefit," she said.

"Sometimes we have multiple trainings," said general manager John Drum of ASM Global, which operates the stadium. "We're training all year long. We're hiring all year long so this is not a space that would go dormant."

Board members Sayles Belton, Angela Burns Finney and Bill McCarthy voted to proceed with the projects. Tony Sertich was absent.

Vekich said that for the stadium operation to stay at "the top of our game," the sports authority must evaluate the quality and efficiency of the four club spaces on game days and for unrelated events.

"I would describe this as a continual improvement of the guest experience," he said.

The four spaces — the Little Six Casino's Club Gold, Factory Motor Parts Club, the Truss Bar and Lumen Lodge Bar — are exclusive club areas on Vikings game days that require specific tickets. The rest of the year, they're rented for events such as parties and conferences.

The 1,450-seat Little Six club is on the 200 level of the north side of the stadium and has almost 9,500 square feet of lounge space. On the opposite side and also on the 200 level, the Factor Motor Parts Club has 1,450 seats and 11,600 square feet of lounge space.

The Truss Bar is about as high as fans can get in the stadium, on the east end of the building on the upper suite level, with a capacity of 150. The Lumen Lodge, a ticketed and all-inclusive area for groups to watch games, is just down the hall from the Truss Bar.