Neighbors said it's how politics should work.

After months of arguing and deliberating, the Planning and Zoning Commission voted 6-3 to deny an application by Silver Hill Hospital for a special permit to expand into its recently purchased house at 225 Valley Road.

Members of the commission who voted against the special permit argued that, among other reasons, the expansion of Silver Hill was not in harmony with the development of the neighborhood, given the protestations of many neighbors.

Over the summer, these neighbors banded together to form the Silvermine River Neighbors Association in opposition to the project. Many of them came out to each public hearing and made their voices known.

"The criteria include that intended use shall be in harmony with the appropriate and orderly development of neighborhood and that planned activities will not hinder adjacent land," commissioner Dick Ward said. "We have received a lot of testimony from neighbors that would be inconsistent with meeting those criteria."

Silver Hill purchased the 5,700-square-foot house in December 2012 for $2.4 million. The hospital planned to add three bedrooms to the house, for eight patients and five staff members. Silver Hill is a renowned psychiatric hospital that covers 60 acres in the Silvermine part of New Canaan.

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Silver Hill's public relations department referred questions to its president, Dr. Sigurd H. Ackerman, who was unavailable for comment.

Many of the fears neighbors shared were related to Silver Hill growing, not just now, but in the future, taking over more of the otherwise residential neighborhood.

"Neighbors had relatively few comments about 225 but very substantial concerns beyond that," Planning and Zoning Commission Chairman Laszlo Papp said, in favor of approving the permit. He said the commission's focus should be not Silver Hill as an institution, but on this particular property.

But others said if this property even exacerbated at all the pre-existing issues neighbors have with Silver Hill, the permit should be denied.

"The regulations don't say there should be a little adverse impact and it's OK, they say that there shall be no adverse impact," commissioner Michael Crofton said. "In the absence of a master plan, property values in this area will be negatively affected as well, that makes common sense."

In the end, his argument carried the day.

"I was holding my breath there," Barry Levinson, a member of the Silvermine River Neighbors' Association, said. He added that no one in the neighborhood is saying Silver Hill shouldn't exist, and noted that he and his wife are actually financial donors to the institution. "The best part of this is that they say politics begins at the local level, and we saw evidence was brought and they deliberated and decided."

twoods@bcnnew.com; 203-330-6582; @Woods_NCNews