Compare ADU zoning rules across 2 Illinois cities. Average ADU score: 7.0/10.
Gathered from the 2 cities below, with the bill or ordinance each one names. Statewide measures are listed once with the cities they reached, rather than repeated for each.
Statewide law sets a floor; the numbers that decide your project are local. Here is the spread across the 2 Illinois cities covered here, taken from each city's own ordinance rather than a state summary.
| Question | Across Illinois |
|---|---|
| Are ADUs permitted? | 2 of 2 permit them. |
| Detached size cap | Median 1,000 sq ft, from 1,000 to 1,000 sq ft across the 1 cities publishing a numeric cap. |
| Owner-occupancy | Required in none of them. |
| Build cost | $140,000 to $350,000 depending on city and unit type. |
| Easiest and hardest here | Chicago scores 7/10; Evanston scores 7/10. |
Recomputed whenever a city page changes, so this and the city pages below cannot disagree.
| City | Max Size | Setbacks | Permit Fees | Build Cost | 1BR Rent | Score |
|---|---|---|---|---|---|---|
| Chicago | any size that fits the coach house bulk rules; Chicago sets no floor-area cap since the pilot's seven-hundred-square-foot dwelling-unit limit was repealed with the citywide ordinance (effective April 1; see recent changes). What sizes the building: 22 ft height limit, one dwelling unit per coach house, a 15 ft gap behind the main house, the rule that all accessory buildings together may cover no more than 60% of the required rear setback area, and a 3 ft open strip along one side. Coach houses are exempt from floor-area-ratio, lot-area-per-unit and rear-yard open-space minimums but may not eat into open space the main building needs | 2 ft from the rear lot line where the lot backs onto a public alley, waived if the coach house is at least 10 ft from the alley centerline as shown on a survey (17-17-0309). A coach house is one of the few structures allowed inside the required rear setback, but all accessory buildings together may occupy no more than 60% of that setback area (17-9-0201-D). A minimum 15 ft separation is required between the rear wall of the main house and the front wall of the coach house; on lots less than 125 ft deep the Zoning Administrator can cut it to 10 ft by administrative adjustment (17-9-0201-F(8), 17-13-1003-PP) | $2,525-$3,050 for a new coach house in 2026 permit records (DOB building permit fee minimum $2,450 for new residential construction in Table 14A-12-1204.3(3), plus a $75 zoning review fee on most permits; a few paid $1,500 zoning fees). $1,875-$3,150 for a conversion unit (minimum $1,800 for a permit that adds a dwelling unit, Table 14A-12-1204.3(4), plus zoning). The formula is construction factor x review factor x floor area (14A-4-412.2.2.1; $0.44 per sq ft x 0.75 for a wood-frame Group R coach house), so the minimums govern any ADU-sized project. A $300 deposit is paid at application (14A-12-1204.1). DOH lists no pre-certification fee; an affordable ADU costs $500 to register | $150,000-$350,000 | $1,500-$2,200/mo | 7/10 |
| Evanston | 1,000 sq ft | 12 feet | the previous '$2,500-$4,000' had no traceable source. Fees follow the City's building permit fee schedule; request a quote from Building & Inspection Services. | $140,000-$280,000 | $1,500-$2,000/mo | 7/10 |
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