They used to be known as carriage houses or mother-in-law apartments. Today they’re commonly called granny flats, though the technical term is “accessory dwelling units” — ADUs for short.

Whatever the name, they’re at the center of an intense debate in St. Paul’s upscale St. Anthony Park district, where residents are weighing whether to seek zoning changes that would allow single-family homeowners to add ADUs on their property.

The same buzz is building at St. Paul City Hall, where planners are fine-tuning an unrelated proposal to allow ADUs within a half-mile of University Avenue along the new light-rail Green Line. In Minneapolis, where ADUs already are allowed in part of the Phillips neighborhood, city staffers are researching the pros and cons of permitting them citywide.

“Our hope is to start engaging the public on ideas in late spring or early summer,” said Jason Wittenberg, who manages Minneapolis’ land use, design and preservation office.

Supporters say that the small secondary homes — which can range from a unit attached to an existing house or built over the garage to a separate cottage in the back yard — are energy efficient, give seniors the twin benefits of independence and proximity to family, are affordable to 20-somethings and can provide rental income for downsizing residents.

“We see this as actually extending the flexibility of current housing,” said Phil Broussard, an architect who chairs the subcommittee that hatched the proposal. “It opens up opportunities for us that we don’t have right now.”

But others fear that accessory dwellings would compound density, block views and shrink green space along the neighborhood’s winding streets, while adding clusters of unwelcome new rentals to blocks of single-family homes.

“It’s going to change the character of the neighborhood,” said Brad Engelmann, an accountant who sits on the district council board.

Since last fall the community newspaper, the Park Bugle, has published a number of articles and letters on the issue. The district council website features page upon page of resident commentaries, which as of last week ran 2 to 1 against permitting ADUs.

Perhaps the best measure of interest was registered the evening of April 3, when, despite a brewing snowstorm, more than 60 residents jammed the district council’s offices for a meeting on ADUs.

“I’ve been here eight years. I’ve never seen a meeting like this,” Executive Director Amy Sparks said.

Another housing option?

A number of metro-area suburbs, including Bloomington, Roseville and Shoreview, have allowed ADUs for years. But few reportedly have been built, at least partly because they’re so tightly regulated; for instance, a lot size of 11,000 square feet is required to build one in Bloomington.

The concept hasn’t been seriously considered for an established urban neighborhood like St. Anthony Park, where single-family lots are smaller and off-street parking more limited than in the suburbs. ADUs aren’t considered duplexes because they’re smaller than the main house and share utilities with it.

St. Paul began looking at ADUs a few years ago to increase density and keep housing affordable near the new light-rail stretch along University Avenue, city planner Sarah Zorn said.

“It’s just one of many tools to provide more housing options and accommodate more of the expected population increase in the Central Corridor,” she said.

The half-mile ADU zone north of University being considered by the city includes most of the south St. Anthony Park neighborhood. Most of the lots where ADUs could be built are north of University farther east, between Fairview and Western Avenues.

But the issue is most hotly contested in the area of St. Anthony Park north of Energy Park Drive, where the great majority of the neighborhood’s single-family homes are located — about 96 percent on lots of at least 5,000 square feet, and therefore eligible for ADUs under current drafts.

Unknown consequences

The idea of using granny flats in St. Anthony Park emerged last year out of a district council effort to save energy and reduce greenhouse gases. A subcommittee noted that the number of area homes with just one resident was increasing, and thought that ADUs could reduce per capita energy usage.

“ADUs aren’t going to solve it, changing light bulbs won’t solve it, driving an energy efficient car won’t solve it, but they’ll all help,” said Michael Russelle, a soil scientist who sits on the district council.

Meetings last year drew mostly supporters of the idea. In January local architects displayed attractive renderings showing how ADUs might fit into existing lots. But it was the growing (and mistaken, officials said) perception that the district council was about to bless ADUs that drove the heavy turnout on April 3.

Broussard tried to reassure skeptics that the proposal would require owners of ADUs to live on the property, that all accessory buildings (including garages and sheds) on one lot could cover no more than 1,000 square feet, and that the floor area of an ADU could be no bigger than 950 square feet.

Then came the questions: How do you enforce the regulations? Who’s asking for this? Won’t trees have to come down to make room? Where will people park? Won’t my taxes go up? Will they cheapen the look of the neighborhood?

A few said that ADUs would usher in more diversity, build a more vibrant neighborhood and boost area merchants.

“We want a mix of young and old living here,” said resident Jon Schumacher. “We don’t want to see people leaving St. Anthony Park because they can’t find a place to live here.”

But Schumacher and others with similar views were outnumbered by residents such as Glen Skovholt, a former Honeywell executive and Metropolitan Council member who urged caution.

“This is a long-term decision that’s going to last for many years, and I don’t think we have any idea as to the consequences,” he said.

After two hours of debate, the district council’s land use committee tabled a vote on the proposal. Talk turned instead toward forming a working group for more study over the next year and to get a better handle on where people stand.

“We’re aiming for balance, and people that are willing to explore the questions with each other and lay out the issues more completely,” Sparks said.