Complete 2026 cost breakdown: construction, permits, financing, and expected rental ROI.
Calculate your Chicago ADU cost →Building an ADU in Chicago costs between $150,000-$350,000 for new construction, with per-square-foot costs averaging $200-$400. These figures include design, permitting, site preparation, and construction. The most affordable option is a garage conversion at $75,000-$200,000, while prefab/modular ADUs fall in between at $125,000-$250,000.
| Cost Category | Estimated Range |
|---|---|
| Architectural Plans | $3,000 – $15,000 |
| Permits & Fees | $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 |
| Impact Fees | $522 per new dwelling unit under 800 sq ft in 2026, $1,044 for 800-1,599 sq ft, under the Open Space Impact Fee (Chapter 16-18 as amended in 2024: 87 sq ft of open space per person x $20 per sq ft x a 30% developer share x an estimated household size of 1 under 800 sq ft or 2 for 800-1,599 sq ft); it rises to $626 and $1,253 on Jan. 1, 2027 and a registered affordable ADU pays a flat $100. Both conversion units and coach houses are expressly subject to Chapter 16-18 (17-9-0131(2), 17-9-0201-F(11)). Chicago charges no other development impact fee; water and sewer connection fees are billed separately by the Department of Water Management |
| Site Prep & Foundation | $10,000 – $35,000 |
| Framing & Structure | $15,000 – $45,000 |
| Plumbing | $8,000 – $20,000 |
| Electrical | $5,000 – $15,000 |
| HVAC | $3,000 – $8,000 |
| Interior Finishes | $15,000 – $40,000 |
Quotes for the same ADU commonly vary 20–40% between builders. We pass your request to up to 5 local builders serving Chicago, where we have them — free, no obligation.
Get Chicago builder quotes →Permit fees in Chicago are $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. The review timeline is not published by DOH or DOB. City permit records (Chicago Data Portal, permits issued January-September 2026 for a coach house, conversion unit or ADU) show Standard Plan Review permits issuing a median 120 days after the application date (middle half 78-183 days) and Self-Certification permits a median 58 days (35-98 days); DOB says self-certified applications typically issue within 10 business days after zoning approval. Add the DOH pre-certification review before either, with plan check: DPD zoning review comes first on every application; DOB then routes the drawings to its technical reviewers (building, structural, electrical, plumbing, mechanical, fire) through ProjectDox, with the balance of the permit fee due when the permit is ready. Plans must show the DOH pre-certification letter, the coach house height (22 ft), the 15 ft separation, the 60% rear-setback coverage calculation and the alley setback. Chicago has no ADU-specific plan checklist; the Standard Plan Review flowchart and the Self-Cert program pages are the published guidance. Impact fees are $522 per new dwelling unit under 800 sq ft in 2026, $1,044 for 800-1,599 sq ft, under the Open Space Impact Fee (Chapter 16-18 as amended in 2024: 87 sq ft of open space per person x $20 per sq ft x a 30% developer share x an estimated household size of 1 under 800 sq ft or 2 for 800-1,599 sq ft); it rises to $626 and $1,253 on Jan. 1, 2027 and a registered affordable ADU pays a flat $100. Both conversion units and coach houses are expressly subject to Chapter 16-18 (17-9-0131(2), 17-9-0201-F(11)). Chicago charges no other development impact fee; water and sewer connection fees are billed separately by the Department of Water Management. Pre-approved plans: Not available. Chicago has no pre-approved coach house or conversion-unit plan program as of September 2026; DOH's resources page lists guides (the NHS Better Basement Units Guide and a ULI video series) rather than plan sets, so budget for custom architectural drawings.
| 1-Bedroom Rent | $1,500-$2,200/month |
| 2-Bedroom Rent | $1,800-$2,600/month |
| Annual Rental Income (est.) | $22,200/year |
| Payback Period (est.) | 11.3 years |
| Short-Term Rental | No. A conversion unit, or a coach house established after May 1, 2021, may not be rented, leased or offered for transient occupancy as defined in Sec. |
| Overall ROI Estimate | 8-12% gross rental yield on a $175,000-$300,000 coach house renting at $1,600-$2,200/mo, before taxes, vacancy, insurance and financing; a $65,000-$150,000 basement conversion renting at $1,400-$1,900/mo returns 12-25% g. |
A typical ADU in Chicago generates approximately $22,200 per year in rental income based on average 1-bedroom rents. At an average construction cost of $250,000, the estimated payback period is 11.3 years — before accounting for the resale value the ADU adds, which an appraiser determines from comparable sales in Chicago and varies by market (often less than build cost).
1. Garage conversions save 40-60% vs new construction since the shell already exists. Average cost in Chicago: $75,000-$200,000.
2. Prefab/modular ADUs offer predictable pricing and faster timelines. Average: $125,000-$250,000.
3. Pre-approved plans — Chicago does not offer a pre-approved/standard ADU plan program yet, so budget for custom architectural plans (typically $3,000-$15,000). See which cities offer pre-approved ADU plans.
4. State grants — California's CalHFA ADU grant (up to $40K) is currently paused; check calhfa.ca.gov/adu for status and your state for active programs.
5. Get multiple bids — ADU contractor pricing varies 20-40% for the same project. We recommend getting at least 3 quotes.
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