The developer of a construction site on West 66th Street wants to build a 775-foot residential tower with views of Central Park.

But last month, the city put a halt to that plan because 160 feet of the height, roughly 16 floors, was reserved for air conditioning and other mechanical equipment, a massive amount aimed at pushing upper-floor apartments higher.

The proposed building, which would tower over everything else in the neighborhood, is the main reason the City Planning Commission is now looking to limit so-called mechanical voids in residential buildings.

Under current rules, such mechanical space doesn't count toward a building's height. Some developers have begun making those mechanical spaces larger than necessary, allowing them to build higher. At least seven buildings with huge mechanical spaces have been erected or are in the planning phase.

"All they do is drive up the height of the building so that the owners can get a better price for the condos at the top," Manhattan Borough President Gale Brewer said. "That is not what the purpose of a mechanical void is. It's to provide mechanicals for the building, but not to increase the heights of the building."  

The Planning Commission proposal, sent to community boards for comment, would close the loophole by requiring that any mechanical voids taller than 25 feet count toward the total allowable floor space. Some elected officials want to go even further.

"We're not including commercial buildings," said Helen Rosenthal, who represents the Upper West Side, after a recent Community Board Seven meeting. "We're not including many of the suggestions that have come up tonight, which is to limit the number of mechanical void spaces in any building."  

Assemblywoman Linda Rosenthal has her own plan before the state legislature, which would trump whatever the city does. She wants void spaces exceeding 5% of building height to be counted toward the size of the structure.

"What we are trying to do is do a comprehensive review and address the gaps that developers have been so successful at taking advantage of," said Rosenthal, who represents the Upper West Side.  

It will take time for City Planning's proposal to move through the process. As for the building on 66th Street, its fate might end up in court, since the city had given the green light to the plan before it stopped it.