Providing a way to keep relatives close, but not too close, little houses and additions called mother-in-law apartments or "granny flats" are popular on the East and West Coasts. But they are not as common in the Twin Cities.

That may be changing.

Bloomington, which now prohibits such development, is moving toward approval of an ordinance that carefully lays out how such units can be added without spoiling the character of single-family neighborhoods. Officials there say they're doing so partly at the prodding of regional planners who believe "accessory dwelling units," as they're called, can increase the stock of affordable housing.

In reality, they're most often used as a way for homeowners to provide a close but separate residence for aging parents or for sons or daughters who just graduated from college but can't afford to find a place of their own.

Stillwater has allowed the units since 1997.

"We had a lot of inquiries and pressures at the time in our historical neighborhood to make allowances for retired parents," said Bill Turnblad, the city's community development director. In reality, most turned out to be for "adult children who were just starting out, or ... simply for husbands or wives with workshops who wanted to work late and not disturb the rest of the family."

Bloomington's survey of the largest cities in the metro area found that only three -- Minneapolis, St. Paul and Plymouth -- allowed granny flats. Eagan, Coon Rapids, Eden Prairie, Burnsville, Maple Grove and Woodbury all prohibited them.

In municipalities that allowed them, including Apple Valley, Chanhassen, Long Lake, Minnetonka and White Bear Lake, the rules vary widely. Apple Valley allows a second small residence only if a lot is at least 40,000 square feet. In Chanhassen, homeowners who receive a variance for the structures must demonstrate a need based on disability, age or financial hardship. Minneapolis allows them to be built in only one neighborhood. Some cities require the units to be built as additions to garages. Others prohibit it.

Bloomington planner Michaela Ahern researched granny flats and found that they're popular in places like Seattle and Portland, where historically housing has been at a premium. In California, she said, a state law was passed that requires cities to have provisions allowing construction of such units. But they haven't been as popular in the Midwest.

Said Turnblad: "There is in the Midwest a feeling that the largish single-lot family home is the ideal dream home, and once you're in a neighborhood like that there is resistance to sharing it. And I think in the Midwest, we're a little more conservative in following trends."

The proposed Bloomington ordinance, which the Planning Commission supports and will go to the City Council in June, would require that a new unit be attached to the primary dwelling on a lot. It would have to have a separate entrance from the main house, be between 300 and 960 square feet in size, and contain a kitchen, bathroom and bedroom. The addition also would have to be built in the same style as the existing house.

Under the proposal, granny flats could be built only on lots that are at least 11,000 square feet in size and are zoned for single-family residential units.

While the rules for construction would be fairly strict -- there would have to be a firewall and sound insulation between the main house and the granny flat, for instance -- Bloomington has tried to minimize the red tape involved in getting building approval. Homeowners would have to deal only with city departments for permits and would not have to sit through hearings or go before the City Council for approval.

That's on purpose, Ahern said. The city knows such units already exist, she said, and there's no plan to go out and penalize people who built them. But the city would like to track their development.

"We think that having a lot of barriers would serve to discourage these," Ahern said. "We want them to be an affordable option for people."

Ahern said the city expects most Bloomington residents who are interested in a granny flat will build one for a child who's just out of college or for elderly parents. Turnblad said that's what Stillwater expected when it passed its ordinance a dozen years ago.

He estimates there are a couple of dozen such units in the city now. The most common reason for building, he said, is to create studios or offices for people like professional photographers who want to work late at night without disturbing their families.

"We don't have as many mother-in-law [units] as we expected," Turnblad said. "There's a different demographic using it."

The biggest barrier for homeowners who want to build a granny flat has been finding enough parking space to meet the requirement that a lot have two parking spaces each for the main home and the granny flat, he said.

Ahern said that could be an issue in Bloomington as well. Homes with a granny flat would need four off-street parking spaces, and at least two must be in a garage or a place where a garage could be built.

Especially in older neighborhoods on Bloomington's east side, that could be a problem, she said.

Mary Jane Smetanka • 612-673-7380