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Chicago’s ADU ordinance was introduced — see what you could build

Published on May. 19, 2020 by Steven Vance

Updated on Jul. 1, 2020

Chicago’s ADU ordinance was introduced — see what you could build

The moment has finally arrived. The ordinance to re-legalize coach houses and other types of accessory dwelling units (ADUs) was introduced to City Council on Wednesday, May 20, 2020. The new law would allow property owners to add one or more dwelling unit to their houses and vacant lots without needing an expensive and tentative zoning change.

If adopted, the new ADU ordinance — O2020-2850— would take effect on August 1, 2020. That happens to be the same time when the 2019 Chicago Building Code — based on IBC 2018 — becomes mandatory for all renovation and new construction projects.

I would like to thank all of the people at the Buildings, Housing, and Planning & Development departments (I’ve listed their names at the end), and Alders Matt Martin (47th) and Harry Osterman (48th), who drafted this and put it forward. Now that it’s been introduced it can be heard by Zoning and Housing committees. The chairs of those two committees, Alders Osterman and Tunney, have agreed to hold a joint meeting to discuss the ordinance.

A rear (coach house without a garage) in West Town. Photo by Gabriel X. Michael

This question and answer-style article is based on the best of my understanding of the introduced ordinance; don’t think of this as an interpretation of zoning code, as that is purely the domain of the zoning administration staff. I may improve or correct this article at any time. (Updated May 23, 2020, to add new questions about existing non-conforming units

  1. What’s being legalized?

The ordinance would allow one or more dwelling units to be added as a coach house or to an existing residential building without requiring a zoning change. The ordinance divides ADUs into two types:

  1. coach houses, which are the small buildings in the rear of a lot with or without a garage (common across Chicago), with one dwelling unit
  2. conversion units, which are the other types of dwelling units, via additions and renovations in existing buildings 20 years or older. Only units built according to this code would be considered conversion units; units that exist on or before July 31, 2020, that seem like conversion units are not considered conversion units.

2. What kind of ADU could I build on my property?

Interested homeowners and landlords would have to choose which type of ADU would be most appropriate for their property and budget. We’ve created a directory of architects and developers in Chicago who have said they want to design ADUs for Chicagoans.

To help everyone visualize what’s going to be possible, Mark Pomarico and James Young, architects at the firm Booth Hansen, designed these posters showing many of the unique layouts that would be allowed under this ordinance. Other architects may design additional layouts!

Booth Hansen architects Mark Pomarico and James Young created these graphics to illustrate ADU designs that would be legal upon adoption of the ordinance.

3. How many ADUs could be built on a property?

Property owners in “R” zones can choose to add either one or more conversion units or a coach house. Coach houses would not be able to be built on any lot that has a conversion unit.

If adding conversion units

Owners of single-family houses that are 20 years or older would be able to build one “conversion unit”. All other residential buildings that are 20 years or older would be able to add 33 percent of the number of existing units, and rounding up or down.

  • 2-flats: 2x0.33 = 0.66 rounding up to 1 unit
  • 3-flats: 3x0.33 = 0.99 rounding up to 1 unit
  • 4-flats: 4x0.33 = 1.32 rounding down to 1 unit
  • 5-flats: 5x0.33 = 1.65 rounding up to 2 units
  • 6-flats: 6x0.33 = 1.98 rounding up to 2 units
  • And so on.

If adding a coach house

All properties that are either vacant or have a single-family house, 2-flat, 3-flat, or 4-flat would be able to add one coach house as long as there is no conversion unit on the lot.

4. Would any of the ADUs have to be affordable?

Some of them may need to be rented affordably. When two or more conversion units are being added to a residential building (that has five or more units), either at the same time, or at different times, 50 percent of them (always rounding down) have to be rented at an affordable price. The affordable rental price would be required for 30 years.

The affordable price would be determined annually as the rent equal to 30 percent of the income of a household earning 60 percent of the area median income (AMI). Using the Chicago Department of Housing’s maximum rents table, the 60 percent AMI for a two-person household is $42,780. Thirty percent of that $12,834 per year, or $1,069.50 per month.

That probably doesn’t sound affordable, and it’s not affordable to a lot of people. Allowing ADUs are one part of a comprehensive affordable housing policy in Chicago, and this is a start. The ULI ADU task force discussed and recommended many funding and financing ideas that the Chicago City Council would need to design and adopt.

The designated affordable conversion units are different than affordable units in new construction housing that’s required by the Affordable Requirements Ordinance (ARO). ARO units are income restricted.

Conversion units would not be income-restricted and could be rented to anyone regardless of income. This accomplishes two things: It reduces the burden on property owners and the Department of Housing to verify the income of a potential renter, and it ensures that undocumented tenants are not checked.

5. Where in Chicago could an ADU be built?

Coach houses and conversion units would be permitted, as of right, in all residential districts starting with RS-3. That means they would be allowed, without a zoning change, in RS-3, RT-3.5 (a rare district), RT-4, RM-4.5, RM-5, RM-5.5, RM-6, and RM-6.5.

That is great news because RS-3 and RT-4 are the most common residential zoning districts in Chicago, covering the vast majority of “R”-zoned areas.

As for RS-1 and RS-2, property owners in those areas would have to obtain a special use permit via the Zoning Board of Appeals. They would most likely have to hire lawyers and independent experts. The ULI ADU task force recommended a more accommodating policy, saying that the option to build an ADU should be permitted in all zoning districts.

There are some community areas where RS-1 and RS-2 are the dominant residential zoning district. In Ashburn, 94.7 percent of properties in “R” districts are in RS-2 districts, meaning that the owners of over 11,800 properties would have to go to the Zoning Board of Appeals (ZBA) to get permission to build a conversion unit or coach house.

Requiring that ADUS have a “special use” from the ZBA in these two zoning districts would limit the effectiveness of the ordinance in many communities, and inhibit the flexibility of a homeowner to add a unit to reflect changes in their household and family. For example, many ADUs in the United States are built for elderly parents, adult children, friends and family with disabilities who need to live close to a caregiver, and college students.

6. Could a coach house be built with a new construction house or multi-flat?


7. Could a coach house be built on a vacant lot?

Yes. A coach house would be allowed to be built prior to the construction of a “front” house (which is called a principal building in zoning code jargon).

This will be a great policy as it will give vacant lots a new lease on life. Chicago’s 10,000+ vacant lots can be developed sooner with smaller and less expensive housing, perhaps with modular construction.

8. How big could a coach house be?

The ordinance would limit coach houses to 22 feet in height. The two-story + loft coach house on the rear of the lot where I live in Humboldt Park is a hair under 24 feet tall.

The ordinance would limit a coach house’s footprint to 60 percent of the required rear setback, and a floor area of 700 s.f.

Minimum sizes are influenced by the existing building code rules on the minimum size of bedrooms.

9. Could existing coach houses be modified?

Yes. The current zoning code allows only incidental repairs and normal maintenance, but the ADU code would allow expansions to the area and height extents described above.

10. How big could a conversion unit be?

The ADU ordinance doesn’t have direct limitations on the size of the conversion unit. The size of the conversion unit would be determined by a combination of the owner’s desire and the zoning standards as they apply to the existing building’s height and envelope (bulk). The minimum lot area (MLA) and minimum lot area per unit standards would not apply.

Practically speaking, here’s what that means. Say you own a 2-flat on a standard lot size of 3,125 s.f. and the lot is zoned RT-4 (this is one of the most common building scenarios in Chicago). The allowable floor area for that 2-flat is 3,750 s.f., but the units are each 1,300 s.f. totaling 2,600 s.f. of floor area. There is a remainder of 1,150 s.f. This 2-flat can gain a third unit, as an added floor, up to the allowable building height of 38 feet, or in a converted basement.

Depending on other zoning standards that may apply to the lot’s setbacks and yard requirements, a rear addition may be allowed.

11. Could the ADUs be rented on short-term rental websites, like Airbnb?

Not really, because rental periods of 31 or fewer consecutive days aren’t allowed. I guess you could use a short-term rental website to rent a unit out for longer than 31 days.

However, a new conversion unit or coach house could be rented for free to any member of an owner or tenant’s household for any length of time, including for a period of 31 or fewer consecutive days. This rule would not apply to conversion units and coach houses that existed on or before July 31, 2020.

12. How much parking would be required?

No parking is required for conversion units or coach houses. When building a coach house, the existing required parking must remain. However, the ordinance would reduce the required parking for single-family houses in the RS districts from two spaces to one space, allowing the removal of a space in order to flexibly situate a new coach house on a lot.

13. Does this ordinance abolish single-family-only zoning?

Almost. While single-family-only zoning is a detriment to cities because of the pattern of segregation and unaffordable housing it has left in its wake, the ordinance isn’t the same as eliminating Chicago’s single-family-only zoning of RS-1, RS-2, and in most cases RS-3. This is because a conversion unit would be allowed only in buildings that are 20 years old or older, and the ordinance proposes zoning entitlement limitations in RS-1 and RS-2 zoning districts.

14. How would existing non-conforming units be treated?

Existing non-conforming units are non-conforming for one or two reasons: (A) the zoning standards for the lot do not allow an additional unit, or a unit exceeding a certain size; (B) the unit does not comply with the building code.

To resolve both situations, the unit could become conforming without a zoning change by the owner submitting plans and pulling a building permit.

It’s possible that a non-conforming unit that complies with the building code (B) but not the zoning code (A) could request a Department of Buildings inspection, but this is my guess as such a rule has not been established or proposed.

15. How would the affordable conversion units be enforced?

The proposed ordinance would enforce the affordability requirement for those conversion units subject to the affordability requirement in a few ways. When a conversion unit that must be rented at the affordable rate set by the ordinance would be established, it would have to be registered with the Department of Housing, and a notice identifying the conversion unit would have to be recorded against the property with the Cook County Recorder of Deeds. The notice becomes the public record that the unit is an affordable conversion unit and serves as notice to subsequent property owners.

Additionally, each year, the owner of affordable conversion units would have to submit an affidavit to the Dept. of Housing “certifying” that the unit is being rented at the rate calculated by the ordinance. The rules for submitting the affidavit and the evidence required would be developed after the ordinance is adopted.

16. Who at City Hall drafted and shepherded this ordinance introduction?

In no particular order: Steve Valenziano, Cyndi Roubik, Paul Williams, Patrick Murphey, Bryan Esenberg, Daniel Kay Hertz, and Grant Ullrich. All of them were also members of the ULI ADU task force.

Editor’s note: Thank you to Anjulie Rao for helping me edit and humanize this article.

Chicago’s ADU ordinance was introduced — see what you could build was originally published in Chicago Cityscape on Medium, where people are continuing the conversation by highlighting and responding to this story.

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