LOS ANGELES — The California Coastal Commission voted Friday to allow Mitt and Ann Romney to move forward with plans to raze their La Jolla beachfront home and replace it with an 11,000-square-foot mansion.

The Romneys, who were at home in La Jolla but did not appear at the San Diego hearing, purchased the 3,000-square-foot home in 2008 for $12 million. The lot sits above a quarter-mile-long cove that is one of the choicest beaches in La Jolla.

“I just met with Mitt and Ann down at the house. They are extremely excited and pleased and can’t wait to build a new home for their family,” said their attorney Matthew Peterson, who represented the couple at the hearing. “My clients are looking forward to building a house where they can have fun with their kids and grandkids. They are very, very happy this is done. It’s been a long process.”

The city of San Diego had approved the Romneys’ plans for a two-story home, with a massive, 4,500-square-foot basement, but a former Dunemere Drive neighbor challenged the permit, claiming it did not conform with the city’s local coastal plan, which is enforced by the Coastal Commission.

Anthony Ciani, an architect who built and until last year lived in a large, three-story home across the street from the Romneys, said the couple inflated the allowable size of their home by wrongly claiming to own the sandy beachfront west of their seawall. Adding 6,000 square feet of sand brought their lot size to about 18,000 square feet, allowing them to build a structure that was more than 1,000 square feet bigger than would otherwise have been allowed under city guidelines, he said.

Ciani also claimed they had privatized a public walkway on the north side of their home, and that the property’s seawall would not withstand storms.

In a report prepared for Friday’s meeting, San Diego city staff and Coastal Commission staff rejected his claims. According to city maps, they said, the Romneys owned the beach in front of their home. They said the disputed walkway on the north side of the home, which is locked on both ends, was private property, and that the seawall was suitable protection for the home, which is set 40 feet back from the beach.

Two commissioners, Dayna Bochco and Jana Zimmer, who voted against the project, said they were concerned that an unbuildable area, such as a sandy beach, was allowed to be used in the calculation of the home’s size.

Zimmer said she was “flummoxed” by that, and called it a “huge red flag, and an unacceptable premise.” San Diego’s planning regulations, she said, “clearly prohibit counting other kinds of unbuildable areas such as canyons and gullies.”

Bochco took exception to the description of the lower level of the home as a “basement” when it’s actually a lower floor dug into the hillside.

“If you’re standing on the beach … you are going to see French doors or sliding glass doors of a first floor that they call a ‘basement.’ We have to define what we really mean as a ‘basement’ on a hillside lot,” she said.

But other commissioners were unpersuaded, and approved the project 7-4.

“This will be very compatible with development in this neighborhood. It’s not going to be intrusive,” said Commissioner Greg Cox. “Right now, it seems like these people have played by the rules that are in place and the proper thing to do is to approve this project today.”

Peterson said the Romneys, who were required to dedicate the beachfront in perpetuity for public use as a condition of their permit, would probably break ground on the project in six months, and that construction would take between 14 and 16 months.

The 2012 Republican presidential nominee and his wife will have no shortage of shelter during that time. They own a condominium in Belmont, Mass., where he was governor, a summer home on Lake Winnepesaukee in Wolfeboro, N.H., and just purchased a spectacular log mansion in Park City, Utah, that had been listed for $8.9 million.

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