Facebook's billionaire CEO Mark Zuckerberg is preparing for a major update to his digs in the Crescent Park neighborhood, where he plans to raze four homes and build four new ones, equipped with large basements and small crawl spaces.

The Palo Alto resident last week submitted an application to the city's Planning Department to demolish homes at 1451, 1457 and 1459 Hamilton and at 1462 Edgewood Drive. The project description states that the proposed homes "represent approximately half the allowable square footage for the four properties and a 20 percent reduction in square footage relative to the existing homes that will be replaced."

Currently, the four adjacent properties have on them two single-story homes and two two-story homes. Under the new plan, they will be replaced with three single-story homes and one two-story home. The project description from Walker Warner Architects states that the single-family homes will be "smaller, updated versions."

The project description states that three of the homes will use "a simple palette of painted wood shingle siding, natural cedar shake roofing, painted windows and french doors, and stained wood doors where they are solid." Renderings of these homes show low-lying, one-story structures with pitched roofs and heavily landscaped yards.

The fourth home, at 1457 Hamilton, is somewhat different from the other three. It includes white-brick walls, dark steel doors and a metal roof. The project description states that this home "incorporates a more unique character and material palette, in keeping with the variety of architectural styles evident in the surrounding neighborhood."

That, at least, is what would be visible from the street level and what is reflected in the publicly released drawings. The real expansion, a closer look at the plans suggests, will happen underground. Two of the homes would feature basements running roughly along the entire length of the house. In one of the Hamilton homes, the basement will have a floor area of more than 2,400 square feet, which will include a media room, a storage area and elevator access, according to the floor plans reviewed by the Weekly.

Another house would feature a basement with more than 3,000 square feet of space, with two storage areas and a recreation room occupying much of the space.

The basements plans weren't included in the portion of the application that is posted on the city's website (the city doesn't count basement square footage in its floor-area requirements). And despite increasing community concerns about basement construction -- most notably, the extensive groundwater pumping that often accompanies the practice -- the basements aren't mentioned in the letter that Zuckerberg's neighbors received last week, informing them of the new project.

"The plans will reduce overall square footage relative to the existing homes and aim to ensure the new structures and surrounding gardens blend seamlessly with the neighborhood," states the letter from Kimberly Darlington and Alistair Shearer of the property- and construction-management company Darlington & Associates. "While we are still in the planning phase, we wanted to let you know about the project in the early stages and assure you that we will be taking affirmative steps to minimize the duration of construction and related inconvenience in the neighborhood."

The project description on the application notes that the four homes will be "built concurrently to minimize the duration of construction and enable staging that best protects the existing trees on site."

It remains to be seen how neighbors will respond to Zuckerberg's plans. He and wife Priscilla Chan moved into Crescent Park in March 2011, when he also bought the Edgewood home. In October 2013, he bought the three Hamilton properties, reportedly after learning about a developer's plan to purchase the home at 1457 Hamilton and to build a large home on the site.

Zuckerberg ultimately bought the developer's contract with the property owner for a reported $1.7 million, along with $129,000 in deposits that the developer had put down on the property. The purchase later led to litigation, with the developer, Mircea Voskerician, claiming that Zuckerberg had reneged on his verbal agreement to give Voskerician business referrals (the two reached a settlement earlier this year).

So far, the planned compound has sparked curiosity but no opposition from the surrounding community. The Crescent Park Residents Association has not taken a position on the project, said Norm Beamer, the association's president. Beamer said that as long as the homes are to be used as single-family homes for long-term residents, he has no concerns.

Some residents, however, are wondering whether the new homes will be used for short-term use by Facebook employees or VIPs, he said.