CHICAGO -- The proposed modernization of historic Wrigley Field overcame an important hurdle Thursday when the Chicago Cubs and the city reached an agreement allowing the team to build a first-ever electronic Jumbotron and another sign above the ivy-covered outfield walls.

The city's landmarks commission unanimously voted to approve the deal, overcoming opposition from the local alderman and the owners of rooftop businesses who fear their negotiated views of the field will be obstructed.

The matter now goes to the City Council.

The landmarks commission's approval was needed because it must sign off on any changes to historic structures.

Alderman Tom Tunney, whose ward includes Wrigley Field, told the commission that light from the proposed Jumbotron would be seen from blocks away. He asked that its size be reduced.

"I cannot support a proposal that so dramatically affects the quality of life of my residents," Tunney said. "The Cubs often point to large signs at Fenway and U.S. Cellular. Those signs back up to expressways, not people's homes."

The deal would allow the Cubs to erect a 5,700-square-foot Jumbotron in left field of the 99-year-old ball park and a 650-square-foot sign in right field.

Throughout the hearing, commissioners expressed concern that the Cubs were risking changing the ballpark so much that fans would turn away.

"You know you don't appreciate what you have until it's gone sometimes," Commissioner Mary Ann Smith said.

But Michael Lufrano, the Cubs' executive vice president for community affairs, said the team's owners have the biggest incentive of all to make sure fans continue to visit the park.

"We don't want to change it so people won't come," he said.

The agreement, reached after weeks of negotiations, underlines the fact that Wrigley, famous for the storied billy goat curse and Babe Ruth's called home run shot, is unlike any stadium in the United States.

Cubs spokesman Julian Green said the Jumbotron is slightly smaller than what the Cubs initially wanted and the right field sign is significantly smaller. The biggest change is that the Jumbotron would be 95-feet wide instead of 100 feet. That means rooftop bleachers across the street will have less obstructed views than the original design.

But the question looms if the latest deal will trigger lawsuits from the owners of the rooftops that peek over the outfield walls.

The Cubs are in the middle of a 20-year revenue-sharing agreement with the owners of the rooftops. It calls for the rooftops to hand over to the Cubs 17 percent of their gross annual revenue that they earn charging people to watch the games from bleachers they've built atop the buildings.

Cutting into their views amounts to a violation of their contracts and will devastate a multimillion-dollar enterprise that relies on a clear view of the playing field.

The Cubs have said the rooftop views would be "largely preserved," and have pointed out that most of the massive left-field Jumbotron is in front of one of the few buildings that does not have rooftop bleachers.

The Cubs recently brought in cranes to hoist mock-ups of the signs to see just how much they would affect the views. The team has made it clear that minimal impact does not mean no impact.

The signs, particularly the Jumbotron, were the most contentious piece of a $500 million renovation puzzle the Cubs have been trying to put together since the Ricketts family has owned the team.