Mark Zuckerberg's plan to demolish and replace his four homes in Palo Alto's Crescent Park neighborhood took an unexpected turn Thursday morning when the city's Architectural Review Board recommended denying his application, arguing that the proposed "compound" clashes with the city's official vision for single-family neighborhoods.

The board voted 3-1, with Alexander Lew recusing himself (he owns property within 500 feet of the project) and Kyu Kim dissenting, to recommend striking down Zuckerberg's proposal to replace the homes at 1451, 1457 and 1459 Hamilton Ave. and 1462 Edgewood Drive. The plan called for removing a pair of two-story homes and two one-story homes on the four separate parcels owned by the Facebook CEO. They would be replaced with three single-story homes and one two-story home.

In terms of height, density and architecture, the new homes were well within the city's building rules. Even the tallest building, the two-story home at 1457 Hamilton Ave., had a proposed height of about 26 feet, well below the 30-foot height limit in the residential district. The project also included ample landscaping, with trees generally screening the new buildings from the street.

The project architect, Kathy Scott from the firm Walker-Warner Architects, said a major goal of the project was to maintain the character of the neighborhood and reduce the scale of the homes.

Palo Alto's planning staff determined that the architects succeeded in achieving these goals and recommended approving the project. City Planner Graham Owen told the architectural board Thursday that the architecture of the buildings is compatible with the surrounding area and that the sole two-story building is consistent with Palo Alto's "individual review" guidelines for multi-story homes.

But it wasn't the architectural details that bugged the board but a broader issue having to do with the way in which the new buildings would be used. All three of the board members who opposed the application argued that the four homes, while located in a single-family residential zone, are not intended to house four families. This led them to conclude that they cannot make the finding that this project is compatible with the city's Comprehensive Plan, the broad -- and outdated -- document that guides the city's growth.

Peter Baltay noted that the Comprehensive Plan explicitly calls for maintaining the city's residential neighborhoods. The project proposed by Zuckerberg (whose name was never mentioned at the meeting; the applicant is listed as RBLKT LLC, SFRP LLC, RFBPO LLC, and JPAWW LLC) doesn't seem to be consistent with that vision, Baltay said.

"A residence is something where a family lives," said Baltay, the first board member to raise the land-use concerns. "These are not residences. They are part of a larger compound."

When asked by Baltay how the homes will be used, Scott told the board that the idea of the project is "to expand our client's capacity to enjoy the property," which would be shared with friends and family and which, as a result of the renovation, would have more outdoor space.

"The current property is quite restrictive, so this is giving additional space for their residential functions," Scott said.

She also noted that while her client intends to use the four properties in the short term, the idea is to make each building flexible and suitable for use as a single-family home in the future.

But Wynne Furth and Robert Gooyer concurred with Baltay's characterization, with each referring to the project as a "compound" that does not belong in a zoning district intended for single-family homes. Furth argued that the city code limits lot sizes in this district to 20,000 square feet precisely to prevent the loss of homes and the construction of projects that are out of scale with the neighborhood. The four structures proposed for the site, Furth said, "are not credible single-family homes."

"They are credible as part of a larger compound," Furth said. "We have zoning that instructs us that integrated residential use isn't supposed to be more than 20,000 square feet. So I can't make the finding that this is consistent with zoning."

She also noted that while the city doesn't attempt to define a "family," rules specify that each home in the residential district should be an independent housekeeping unit.

Furth and Gooyer also pointed to specific features in each of the homes that would seem irregular in a single-family home, but that only make sense when the buildings are thought of as a single compound.

Gooyer noted that in one of the homes, there is a living room at one end of the home, a kitchen on the other end and a bedroom between them.

"That's not normal," he said. "Once you put all these pieces together, it reads compound."

Furth pointed to each of the four homes and took note of features that aren't well suited to a single-family home. At 1457 Hamilton Ave., for example, plans call for a large entertainment space and what looked like a service kitchen, rather than a family kitchen. The home also includes a downstairs media room, she noted.

"This is a great place for a party, but I don't see as a credible single-family detached dwelling," Furth said.

Toward the end of the hearing, Baltay raised an even broader concern when he questioned the need to demolish the existing buildings at all. He called the four homes "stellar examples of architecture in Palo Alto."

"I find it a real shame that we're tearing down four perfectly fine homes," Baltay said.

With the board's recommendation submitted, it will now be up to the city's planning director to consider the board's findings and to determine whether the project should be allowed to commence.