SOUTH PORTLAND — Proposed zoning changes related to nonconforming house lots won a unanimous recommendation from the Planning Board on Tuesday night.

Triggered by a recent lawsuit, the proposed changes pertain to the construction of single-family homes on nonconforming lots and the required minimum house lot sizes in residential districts. More than 20 requests to build houses on nonconforming lots have been put on hold pending the City Council’s decision on the proposed changes in the coming weeks.

Approved in 2007, zoning regulations related to nonconforming lots have resulted in some houses being built too close together and others being built without board review when they should have been scrutinized, said Tex Haeuser, city’s planning director.

And overall, Haeuser said, current zoning requires house lots to be so large, they’re often out of character with the rest of the neighborhood.

The board invited 6,200 property owners in residential districts to its public hearing at South Portland High School. About 75 people attended, many of them with questions about the proposed changes, which are complicated even for people familiar with zoning regulations.

“I feel like there’s a lot of value in my nonconforming lot,” said Adam Helm of Willard Street, one of more than 15 people who spoke. “I’m at a bit of a disadvantage because I don’t know as much as I should.”

Some residents raised concerns about the drawbacks of developing smaller lots to answer growing demand for affordable housing in the city. Others worried about losing the right to build on smaller existing house lots.

Haeuser explained that the proposed zoning changes would preserve the right to build on existing nonconforming lots recorded at the Registry of Deeds, but they would impose more restrictive standards, including setback and density regulations.

In addition, all proposals to build new homes on legal nonconforming lots would require a public hearing and review by the Planning Board; currently, only homes on lots under 5,000 square feet require the board’s review.

Haeuser said it’s unclear how many nonconforming lots are in the city, but an average of 12 homes per year have been built on nonconforming lots in recent years.

The proposed zoning changes also would reduce the minimum buildable house lot size in many older neighborhoods, where 1960s suburban standards have proved to be too large and limiting, Haeuser said.

Under current zoning, the minimum lot size in a Residential A zone is one-quarter acre or about 12,500 square feet, and in a Residential AA zone it’s one-half acre or about 20,000 square feet. New minimum lot sizes would be based on the median lot size of existing homes in each neighborhood as determined by GPS measurements, Haeuser said.

Minimum lot sizes would be as follows in various neighborhoods: Willard, Pleasantdale and Meetinghouse Hill, 6,000 square feet; Ligonia, 6,500; Stanwood Park, Sunset Park and Thornton Heights, 7,000; Knightville, 7,500; Cash Corner and part of Ocean Street, 8,000; Loveitt’s Field and Meadowbrook, 8,500; Country Gardens and part of Highland Avenue, 12,500; part of Ocean Street, 13,500; part of Highland Avenue and Stanwood Park, 20,000.

As proposed, Haeuser said, the smaller lot sizes would allow about 500 parcels to be divided to create an additional house lot.