PALO ALTO — Facebook CEO Mark Zuckerberg’s plans to rebuild four homes around his own will form a “compound” and reduce the city’s housing stock, which violates zoning codes and ideal land use, a city advisory board decided Thursday in a project review.

The Architectural Review Board voted 3-1 to recommend that city Planning Director Hillary Gitelman not approve Zuckerberg’s application to replace homes at 1451, 1457 and 1459 Hamilton Ave. and 1462 Edgewood Drive.

Concerned about privacy, Zuckerberg bought the homes for $30 million in 2013 after learning that a developer planned to build a house next door tall enough to have a view of Zuckerberg’s master bedroom.

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Mark Zuckerberg giving away 99% of Facebook stock to celebrate daughter’s birth Plans call for removing a pair of two-story homes and two one-story homes.

Replacing those structures would be one two-story home and three single-story homes that are smaller in dimension than the existing homes.

The homes would be 20 percent smaller than what was there and built out to only half of the square footage that is allowed on the lots.

Kathy Scott, of the Walker-Warner Architects firm working with Zuckerberg, said the project seeks to expand her client’s space for “residential functions.”

“The idea is just to expand our client’s capacity to enjoy the property: sharing time with friends and family, having more outdoor space to play,” Scott said. “The current property is quite restricted and so this is just giving them more space for their residential functions.”

The vision of expanding a single homeowner’s “residential functions” is what raised red flags for board members who say that doing so would ruin the single-family home feel of the Crescent Park neighborhood.

Plans for all four homes meet architecture standards, but a single family using all four properties violates the city’s comprehensive plan and ideals in protecting single-family homes, board members said.

“There’s four homes,” board member Peter Baltay said. “Are there four families living in these homes?”

The Zuckerbergs currently have friends living in a couple of the homes and Scott said the other homes are used as an extension of their living, cooking, dining and entertaining quarters.

Baltay said his view is that these four houses are not separate residences.

“These are part of a larger compound,” Baltay said. “This is something you might find in Atherton: A large estate, a series of guest houses, recreational facilities, movie theaters surrounding a house.”

Board members Wynne Furth and Robert Gooyer agreed and said the floor plans for the homes show that they are not “credible” single-family dwellings.

Though each house has basic bedroom, bathroom, kitchen and laundry facilities to count as a standalone, the layout tells a different story.

Furth said one home has two bedrooms, three washers and dryers, a project room off the garage and “a really nice vegetable garden.”

Another home would be altered into a “great place for a party,” with a great room that’s 40 feet by 30 feet, a service kitchen and another larger room in the basement.

“If these things were put on the market individually, you’d have a hard time selling, because some of them are very unusual,” Gooyer said. “In the context, if you take all four of them, they make sense.”

Furth also said the proposal violates the zoning code when considered as a complex because single lots cannot exceed 20,000 square feet as a way to prevent net loss of housing stock.

Together, the four homes exceed 60,000 square feet. That figure does not include the adjacent property where the Zuckerbergs reside.

Combined with the principal dwelling, Furth said the compound is “even bigger and even more out of compliance.”

Scott said there are no plans to merge the lots or adjust lot lines so that the flexibility and independence of the four lots is maintained for future homeowners.

The Zuckerbergs also plan to remove the pools and maximize the garden areas and maintain the variety of trees, including live oaks, ginkgos and magnolias, Scott said.

“They bought the original house and these other properties in the neighborhood because they love the character of the neighborhood; its significant trees and the very residential scale and the variety of homes, and that’s what we’re endeavoring to preserve,” Scott said.

During Thursday’s discussion, Baltay also contemplated out loud to city staff about whether the proposal should undergo the process for seeking conditional-use permits, which would give community members more notice and the City Council an opportunity to consider the proposal’s broad impact rather than on a home-by-home basis.

The project will return to the city’s planning director, who will decide whether to advance the project.

Board member Kyu Kim was the lone dissenting vote, though he did not elaborate much on his decision, and board member Alex Lew recused himself because he owns property nearby.