Chicago Guides

Coach houses & conversion units

Chicago’s ADU rules add a home to a lot in one of two ways: a coach house out back, or a new unit inside a building that already stands. Where each is allowed, and what it has to meet.

coach houseconversion unitChicago’s ADUs

RS districts: only inside the 10 ADU-Allowed RS Areas

Every rule below is cited to Title 17 of the Chicago Municipal Code and links to the section in our hosted zoning code. Affordability terms are set outside Title 17, in §2-44-106 of the Municipal Code.

Definitions

Two kinds of ADU

“ADU” isn’t a Chicago zoning term. The ordinance calls them Additional Dwelling Units only when it maps where they are allowed in RS districts §17-7-0571, and regulates two concrete forms:

Detached

Coach house

A 25 by 125 foot lot seen from the alley: a two-flat at the front and a coach house at the rear, 15 feet behind it, 2 feet off the alley line, no more than 22 feet tall, with 3 feet of open space along one side. ≤ 22 ft15 ftalleytwo-flatcoach house

One unit in its own building at the back of the lot, often over a garage. Seen here from the alley.

Inside

Conversion unit

A three-flat more than 20 years old with a fourth unit added on its garden level: a conversion unit. new unit, garden level3 existing units

A unit carved out of an existing building — typically a garden level or attic — in a building standing for 20+ years.

Heights are drawn exaggerated ×1.3.

Where

Where ADUs are allowed

DistrictsCoach houseConversion unit
RS-1, RS-2, RS-3Only in an ADU-Allowed RS AreaOnly in an ADU-Allowed RS Area
RT-3.5 – RM-6.5PermittedPermitted
B2PermittedPermitted
B1, B3, C1, C2PermittedPermitted above the ground floor; below the second floor, by right only if ≥ 40% of the ground floor on the street is commercial, otherwise a special use
C3Not permittedNot permitted

From the use tables §17-2-0207 and §17-3-0207, with §17-9-0131. Other districts (downtown, manufacturing, planned developments) are not covered here.

In B and C districts, a coach house must also sit in the rear 30 ft of the lot §17-9-0201-F.

ADU-Allowed RS Areas

In the single-family RS districts, ADUs are a pilot: permits may be issued only inside ten designated areas, described street by street in §17-7-0574. Several areas carry extra limits §17-7-0573:

  • Annual cap. No more than 1 (RS-1), 2 (RS-2) or 3 (RS-3) coach houses and conversion units combined may be pre-certified per year on a block face and the opposite block face together.
  • Owner-occupied. If the main building is a detached house, it must be owner-occupied at pre-certification.
  • Administrative adjustment. Each unit needs the Zoning Administrator’s approval §17-13-1003-QQ.
AreaAnnual capOwner-occupiedAdmin. adjustment
Area 1———
Area 2—YesYes
Area 3YesYes—
Area 4YesYes—
Area 5YesYes—
Area 6———
Area 7———
Area 8YesYesYes
Area 9YesYesYes
Area 10YesYes—

Limits by area, from §17-7-0574. Area 1 is the largest, covering much of the North Side lakefront and the central city.

The Department of Housing enforces the RS-area rules at ADU pre-certification, before a building permit §17-7-0572. LotGrade checks each Chicago parcel against the city’s ADU area map and shows the area and its limits.

Coach houses

Coach house standards

Building heightrooftop features also capped at 22 ft above grade
≤ 22 ft
Separation from the main buildingrear wall to front wall; 10 ft by adjustment on lots under 125 ft deep §17-13-1003-PP
15 ft
Open sideclear to the sky along at least one side line, unless it abuts a street or alley
3 ft
From the alley lineunless 10 ft or more from the alley centerline §17-17-0309
2 ft
Unitsper coach house
1
Parkingnone required for the coach house
0

All of these come from §17-9-0201-F, which also says a coach house:

  • is exempt from minimum lot area per unit, from the residential and B/C FAR limits, and from the rear yard open space standards — but may not reduce open space the main building needs;
  • may not be built before the principal building it serves;
  • may let the main building’s required parking be reduced or waived by administrative adjustment §17-13-1003-OO;
  • must stay affordable to the extent §2-44-106 requires; and
  • if established after May 1, 2021, may not be rented short-term to anyone outside the owner’s or tenant’s household, with fines of $1,500–$3,000 a day.

Coach houses are one of the few buildings allowed inside the rear setback §17-17-0309.

Conversion units

Conversion unit standards

A conversion unit is added during the repair, remodeling or alteration of a residential building that has been lawfully in place for at least 20 years §17-2-0303-C.

Existing units (20+ yrs)33%May add
1—1
20.661
30.991
41.321
61.982
92.973

Units that may be added: 33% of the units in the building for 20+ years, with 0.5 and above rounding up; a single-unit building may add one §17-2-0303-C.

Under §17-9-0131, conversion units are exempt from minimum lot area per unit and from the rear yard open space standards, need no parking, must meet the §2-44-106 affordability terms, and may not be rented short-term outside the household. In an RS district the lot must also be in an ADU-Allowed RS Area. See density for how the lot-area standard otherwise caps units.

Questions

Common questions

Are ADUs legal in Chicago?

Yes. Chicago allows two kinds of additional dwelling unit: coach houses (a unit in a detached accessory building) and conversion units (a unit added inside an existing residential building at least 20 years old). They are permitted in RT and RM districts, most B and C districts, and in RS districts only inside designated ADU-Allowed RS Areas (§17-2-0207, §17-3-0207, §17-7-0574).

How tall can a coach house be?

No more than 22 feet in building height, and rooftop features may not exceed 22 feet above grade either (§17-9-0201-F).

Does a coach house need parking?

No. A coach house may be built without parking of its own, and the parking required for the main building on the lot can be reduced or waived by administrative adjustment (§17-9-0201-F, §17-13-1003-OO).

Can I build a coach house on a vacant lot?

No. A coach house is an accessory building and may not be built before the principal building it serves (§17-9-0201-F).

How many conversion units can I add?

Up to 33% of the units that have existed in the building for 20 or more years, rounded to the nearest whole number (0.5 rounds up); a single-unit building may add one (§17-2-0303-C). A three-flat can therefore add one; a six-flat, two.

Can I rent a coach house on Airbnb?

No. Coach houses established after May 1, 2021, and conversion units, may not be offered for transient occupancy to anyone outside the owner’s or tenant’s household. Fines run $1,500 to $3,000 per offense, and each day is a separate offense (§17-9-0201-F, §17-9-0131).

Do ADUs count against FAR or density?

Coach houses are exempt from the lot area per unit standards and from the residential FAR limit; conversion units are exempt from lot area per unit. Both are exempt from the rear yard open space standards, though a coach house may not reduce open space the main building needs (§17-9-0201-F, §17-9-0131).

Keep reading

For a real address

Is this lot ADU-eligible?

LotGrade checks any Chicago address against its district and the city’s ADU area map, shows the area’s limits, and adds the extra unit to the lot’s unit count when a coach house or conversion unit is allowed.

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