Kansas City, Mo. ? Arrowhead Stadium, with the family of the late Lamar Hunt kicking in an extra $50 million, is going to get a $375 million facelift.

Altogether, the 35-year-old home of the Kansas City Chiefs will expand by approximately 500,000 square feet. There will be a roughly 50 percent increase in concessions and an 80 percent increase in bathroom facilities. Concourse width will double. There will be a Chiefs Hall of Fame open 365 days a year and an innovative “horizon level” where fans can watch the game in an outdoor setting from up high.

“Arrowhead as a facility has been the blueprint for NFL stadiums since it opened,” Dennis Wellner, a founding senior principal at HOK Sports said Wednesday at a news conference.

“The question is, how do you improve it? I believe you respect the icon, which is Arrowhead, and you look to the future. Goals for the project are to increase provisions for fans at all levels of the building and match what’s been provided in the newest stadiums in the NFL at a cost of half what a new facility would cost.”

Construction will take about three years and include a new training facility with a 100-yard indoor field and a separate building to house coaches and front office executives.

Voters in Jackson County fearful of losing the Royals and Chiefs, passed a three-eighths of a cent sales tax 15 months ago to fund the ambitious renovation at Arrowhead and its sister facility at the Truman Sports Complex, baseball’s Kauffman Stadium.

As part of the deal, the David Glass family, owners of the Kansas City Royals, agreed to contribute $25 million toward improvements at Kauffman. The Hunt family, sole owners of the Chiefs, originally committed $75 million of their own funds. But on Wednesday, Clark Hunt, chairman of the board of the Chiefs and son of the team’s late founder, announced the family was putting in an additional $50 million, for a total contribution of $125 million.

“There was no obligation under the original lease for the Hunt family to spend one more dollar on this project,” said Jackson County Executive Mike Sanders. “But today the Hunt Family and the Chiefs organization is reaching deep, deep into their pocket to provide an additional $50 million for a stadium that is owned by the taxpayers and by the Hunt family. Arrowhead Stadium is and will continue to be a Jackson County taxpayer asset.”

Hunt said the family made the decision to increase the commitment about two months ago.

“We just decided it was in the best long-range interest of the Chiefs and the Jackson County taxpayers to make the commitment,” said Hunt, 42.

“We felt that to get it right, it was important to go beyond what was required to ensure that Arrowhead remains one of the greatest stadiums for decades to come.”

“These extra dollars will primarily go to audiovisual enhancement, including a 360-degree ribbon board, a hall of honor that will offer our fans a chance to experience the rich history of the Chiefs, and significantly improved team training facilities comparable to the very best in the NFL,” he said.

The private funds also will help pay for the horizon level, as well as a field at the Chiefs training facility that will be available for youth football teams.

Seating 79,541 and perpetually sold out, Arrowhead is the third-largest stadium in the NFL and in the fifth-smallest market. To meet requirements of the Americans with Disabilities Act, Arrowhead will lose about 2,400 seats with the renovation.

Carl Peterson, Chiefs president and general manager, said great care will be taken not to change the stadium’s bowl and to retain the game-day atmosphere.

“We are going to be gutting and redoing 81 suites,” Peterson said. “Our suite holders have indicated they don’t want to sit inside. They still want their seats outside, and that’s what we’re doing. When we do have a full house and rev-up the sounds, it’s pretty intimidating for an opposing player. If we can, we’ll make it louder.”