Minnesota’s extensive, multiyear Capitol renovation will likely cost $30 million more than budgeted, state leaders learned Friday.

Although Gov. Mark Dayton and other officials relented, they were miffed that they were asked to add more money to the already $270 million project.

“I don’t like it,” Dayton said, but added that finding unanticipated needs in the renovation of a 109-year-old building should have been expected.

“It’s not surprising that there’s some unwelcome surprises,” the governor said before a bipartisan commission approved asking the Legislature to front more for the Capitol project.

The request for more cash — largely to deal with the leaky basement and security measures to prevent cars from driving into the Capitol — might not be too hard of a sell for this year’s lawmakers. Recently Legislatures have acquiesced to the long pleas that the Capitol, a century-old masterpiece by noted architect Cass Gilbert, needs help.

The renovation has been underway since late 2013, filling the marble halls with sounds of jackhammers, forcing senators into tiny offices and erecting temporary plywood walls to protect historic structures.

Supporters promise that the four-year project will modernize the building’s interior and spiff up its exterior.

The extra cash might come in the form of a small borrowing bill this year and could include money from the Minnesota Legacy Fund. Or the additional cost might just need to be paid out of the state’s budget.

“The Senate cares deeply about the renovations of the Capitol,” Senate Majority Leader Tom Bakk, DFL-Cook, said. “We’re going to ask the House, if they don’t do bonding, to use cash.”

Still, the new $300 million price tag gave some officials pause, especially since the original $270 million cost already included a $20 million contingency fund. That fund to deal with cash overruns has nearly been exhausted.

During Friday’s Capitol renovation meeting, Rep. Paul Torkelson, R-Hanska, asked how such large unexpected costs could arise midway through the project. The answer: No one knew what lurked inside the bowels of the Capitol.

“We are still are doing demolition work, so we still are discovering new issues,” said Wayne Waslaski, the Minnesota Department of Administration’s point person for the renovation.

The waterlogged basement was part of that discovery. The extra money also will be used to increase security outside the building, including the installation of planters and other barriers to prevent vehicles from driving into the Capitol from Aurora Avenue.

The additional security measures upset members of the Capitol Preservation Committee, which includes the governor, representatives from the public, the Supreme Court and lawmakers from both sides of the aisle.

Most committee members support the project’s plan to all but eliminate parking on Aurora, which snakes directly in front of the Capitol grand steps. But they don’t want the security measures to go too far.

“I just am afraid of having the Capitol armored up,” said committee member Ted Lentz.

The idea of spending an extra $3.25 million to restore the Capitol’s fine art was largely uncontroversial Friday.

The art includes turn-of-the-century paintings of the Civil War, oil paintings fixed to the Capitol Rotunda’s walls and allegorical murals and lunettes throughout the rooms and hallways. Lentz estimated, based on recent sales of similar art elsewhere, that the collection was worth nearly $1 billion.

The most valuable of the art adorns the Minnesota Supreme Court’s chamber. The permanently affixed John La Farge oils on canvas could be worth hundreds of millions of dollars, Lentz estimated. Like the rest of the fine art throughout the Capitol, they show the wear of time — they are faded, scratched and areas are bubbling up.

“How could we possibly neglect this art?” asked Stephen Elliott, director of the Minnesota Historical Society. “It would be a major shortcoming of this otherwise magnificent undertaking. … The final result will be well worth the investment.”

The committee agreed.

In another development related to the renovation, Bakk said Friday that the Senate will move its offices still housed in the Capitol into leased space in downtown St. Paul this summer.

“(The Administration Department) wants us out of the Capitol by the first of June” to make way for renovations, Bakk said.

He said the office space will be bare-bones, with a small number of meeting rooms that senators will be able to reserve.

By 2016, the Senate will move into a new office building behind the Capitol, while the House tentatively plans to use its Capitol chambers next year. Bakk said he thought that plan would be expensive and inconvenient and offered to host the House in the Senate building, too.

House Speaker Kurt Daudt, R-Crown, said the House is unlikely to accept that invitation.

The invite decline is not because the House Republicans have been vocal critics of the new Senate building, he said, but because arrangements have been made.

And there’s another issue: “We are not the Senate, and us being in a space that the Senate controls is also potentially problematic,” Daudt said.

Staff writer David Montgomery contributed to this report.

Follow Rachel E. Stassen-Berger at twitter.com/rachelsb.