After a ban of more than 60 years, City Hall wants to make it legal again to build granny flats and coach houses in Chicago, as a piece of the effort to ease the city's housing affordability woes.

One plank in Mayor Rahm Emanuel's five-year housing plan that will go before the Chicago City Council tomorrow suggests the city should revamp building codes and zoning rules to "create affordable housing through Accessory Dwelling Units (ADUs)." If the council adopts the plan, City Hall would later propose individual ordinances to open up zoning to allow them.

"This will be an opportunity to come back to a traditional (form of) affordable housing," said Steven Vance, a Chicago advocate for modern city planning practices who runs the construction permit-tracking site Chicago Cityscape.

A coach house is typically a small building behind and detached from a main house, originally a place where coachmen or other servants lived. A “granny flat” is a secondary living space in a house, usually in the basement or attic. Coach houses and granny flats were historically accepted, but they were ruled out in the mid-20th century with the advent of tight residential zoning.

Construction of new coach houses has been banned in the city since 1957, when city planners apparently saw them contributing to overcrowding that hurt property values. In the past few years, the opposite has been happening: Affluent neighborhoods have become less dense as many vintage two- and three-flats have been replaced with or rehabbed into single-family homes.

That and rapidly rising housing prices—both for sale and for rent—have contributed to narrowing the range of incomes in some parts of the city.

Reviving granny flats and coach houses could be a partial remedy, the city's plan says. Emanuel's spokesman did not provide a city official to discuss the proposal.

"It makes a lot of sense," said Paul Bertsche, a principal of Chicago-based homebuilding firm CA Development. "It's a wonderful way to provide some flexibility" in a neighborhood's housing options.

Bertsche's firm tried building townhouses with granny flats attached about 15 years ago on Talman Avenue in a part of Logan Square near what later became the 606 trail, but strict city building rules wouldn't allow plumbing other than for a toilet, meaning no full bath and no kitchen. In the end they were more like home offices or rec rooms than ADUs. That turned him off from the idea for later projects in places like Edgewater and Avondale.

Not only would a granny flat in the house or a coach house out back appeal to renters, Bertsche said, but the homeowners might use it in different ways as they move through life stages. "You rent it when you're young and need the money," he said, "and later you have a place to house your kid who boomerangs" back home, or an aging parent.

Creating a fully livable apartment upstairs from a standard two-car garage on an alley would cost about $80,000, Bertsche estimated. He and Vance both said it would be most likely on new-construction homes, in part because tacking that work onto a new-build program would be less expensive and less inconvenient than building a new second story on an existing garage (which may not have been designed to hold the weight, among other things.)

"In a neighborhood where you can rent that 400-square-foot apartment for at least $600 or $800, the extra cost is probably a wash," Bertsche said. In Edgewater, studios of just less than 400 square feet are advertised in that price range on Apartments.com.

Thus in a rare coming together of problem and solution, "you would see these getting built in the neighborhoods where they're needed," Vance said.

Chicago's not alone in looking at the throwback housing type as a solution for today's needs. In September 2017, Oak Park changed its rules to allow coach houses, which previously could not have plumbing, to be plumbed and turned into living space.

"It was a way to integrate some lower-cost housing into our neighborhoods that are primarily single-family homes," said Craig Failor, Oak Park's village planner. The change came about because the owners of several historical homes with coach houses had applied to upgrade the spaces with bathrooms and kitchens, Failor said.

Since the change, he said, there have been few applications to build ADUs, either as part of a new home or in a rehab, though he said it may only be a matter of builders working out plans that fit the new rules.

Allowing ADUs is a way to correct "the misalignment of our houses, which were mostly built in the middle of the 20th century for the nuclear family, and not for our different family configurations of today," said Kyle Smith, director of housing initiatives for the Metropolitan Mayors Caucus, which represents 275 municipalities in northeastern Illinois. "Our demographics and our houses don't match as well as they used to."

Smith said the mismatch exists not only in urban Chicago and Oak Park, but also in outlying suburbs where older homeowners may want to stay in their longtime communities but can't manage a full-size house anymore. Permitting ADUs in those areas would have the added benefit of allowing for "multigenerational living, which most homes out there weren't designed for."

More suburbs may sign on to the idea. The mayors caucus is hosting "Granny Flat Academy" sessions for municipal officials in January in Evanston, north suburban Libertyville and far northwest suburban Woodstock.