They are found all over Chicago but are frowned upon by city zoning rules. Whether that should change is a topic expected to get more discussion this year.

They go by names such as coach houses, carriage houses, granny flats and in-law apartments. The more formal name is accessory dwelling unit, or ADU, and some people think they can help Chicago boost its supply of affordable housing.

These are living quarters that are separate from the main home on a property. They might be in a separate building, or in the basement or attic of the primary residence. They are found all over Chicago but are frowned upon by city zoning rules, which generally forbid new construction of ADUs. Whether that should change is a topic expected to get more discussion this year.

The Urban Land Institute Chicago, an association of professionals in real estate and allied fields, has a task force studying ADUs. The goal, said Swasti Shah, director of community engagement at ULI Chicago, is to produce recommendations for the city on how to do the job right. She said the task force has been meeting since August and hopes to issue a report in May that will include ideas for homeowners and lenders interested in what amounts to a new option in the local residential market.

A task force member, Steven Vance, said the group hopes to have a draft ordinance this month to circulate to Ald. Harry Osterman (48th), chairman of the Chicago City Council’s Committee on Housing and Real Estate. Vance, director of urban planning at the consulting firm MAP Strategies, said ADUs address the affordable housing issue only at its margin, but it’s an important margin. He said it’s a way for the private market to increase the supply without having to ask for government subsidies.

The task force also will need to speak to possible pitfalls of ADUs, of which there are many. Does it promote the influx of substandard housing or noisy neighbors on a block that’s used to quiet? Is it a back-door way to let developers build expensive housing in already desirable neighborhoods? Will it promote too many new rooftops and asphalt when some people still like open space, even if the yards belong to somebody else?

“Consider street parking in a neighborhood. People guard it jealously,” said Joseph Schwieterman, a professor at DePaul University and author of The Politics of Place: A History of Zoning in Chicago. He said the city’s general anti-ADU stance dates at least from its 1957 zoning ordinance. Those in power then were more concerned about uniformity and order than about affordable housing. “Coach houses always have been seen as a big can of worms,” Schwieterman said.

He said loosening the rules for them could relieve the upward pressure on prices in some neighborhoods, but enforcing common-sense standards will be a challenge. What’s to prevent large families from being crammed into a couple of rooms?

Vance said accessory housing will draw popular support. “It’s doesn’t change the visible character of the block,” he said. Also, he said the same people who might protest more density on their block instead might like the ability to add a rental unit for income or a place where an in-law or grown son or daughter can live.

It appears nobody counts this type of housing in Chicago. On his Chicago Cityscape blog, Vance and others used a necessarily rough method to estimate about 2,400 coach or rear houses exist here. They’re all grandfathered under city zoning, except that a unit that hasn’t been occupied by a renter or family member for at least a year legally can’t be used that way again. How many might be added is anybody’s guess. Vance said when Los Angeles liberalized rules for the new units, it got thousands of permit applications.

But Vance said the expense of a stand-alone house means few will get built. If the rules change, the early adopters might be the wealthy who employ costly architects and designers, confirming some of the suspicions about accessory housing, Vance said. But he said over time, the activity will shift to adding basement or attic units that would carry cheap rents.

A word here about zoning. The subject makes people’s eyes glaze. But along with police arrest powers, it is among the most weighty responsibilities of local government. It can make property owners rich, or deprive them of riches. With so much at stake, Chicago aldermen guard their zoning authority zealously, and some have gone to the pokey for abusing their influence.

Imperfect as it is, zoning is still an expression of popular will. Anybody who wants a fundamental zoning change in Chicago will enter a fight that’s about politics, not urban planning.