An ADU builder in Chicago is a licensed contractor who designs and constructs accessory dwelling units — detached backyard units, garage conversions, attached additions, and junior ADUs (JADUs). Because an ADU is a complete second dwelling, the builder coordinates foundation, framing, plumbing, electrical, and HVAC work and pulls it through Chicago's permit process and utility connections. Not every general contractor has built one, so the right builder is one with ADU-specific experience in Illinois.
What ADU Builders Cost in Chicago [5][6]
Based on our Chicago cost data, expect the following ranges from local ADU builders. Quotes for the same scope typically vary 20-40% between contractors, so getting at least three bids is the single best way to control cost.
| New Detached ADU (all-in) | $150,000-$300,000 |
| Cost per Sq Ft | $160-$315 |
| Garage Conversion | $80,000-$180,000 |
| Prefab / Modular ADU (installed) | $110,000-$250,000 |
| City Permit & Plan Review | $2,800-$4,500 |
| Impact Fees | $1,000-$1,800 |
For a full line-item breakdown, see our Chicago ADU cost guide. To confirm what you're allowed to build before you hire, review the Chicago ADU rules (max detached size: Detached coach houses governed by bulk/setback standards rather than a flat sq-ft cap (limited to 60% of the required rear setback area); Confirm buildable size with Chicago Dept. of Housing for your lot; owner-occupancy: Required on properties with 2 or fewer units (West/South/Southeast pilot areas require it for 1–3 units); alderpeople may add owner-occupancy conditions in RS zones).
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How to Vet an ADU Builder in Chicago
- License: Confirm a current contractor's license in Illinois and that it's in good standing. Ask for the license number and verify it with the state board.
- ADU-specific experience: Ask how many ADUs they've completed in or near Chicago and request addresses or photos. ADU permitting and setbacks differ from a kitchen remodel.
- Portfolio & references: Get references from recent ADU clients and, if possible, visit a finished unit.
- Insurance: Verify general liability and workers' compensation coverage. Ask for a certificate of insurance.
- Written, detailed bid: Insist on an itemized, fixed-price or clearly-scoped bid — not a verbal estimate. It should state whether permits ($2,800-$4,500), plan check (3-4 weeks), and impact fees ($1,000-$1,800) are included.
- Permit handling: Confirm they manage Chicago's permit process ("Building permit", typically 60-90 days) and who is responsible if revisions are required.
- Payment schedule: Avoid large upfront payments. A reasonable schedule ties payments to completed milestones.
Questions to Ask Before You Hire
- How many ADUs have you built in Chicago in the last two years?
- Is your bid fixed-price, and what would trigger a change order?
- Are permits, plan check, and utility connection fees included?
- What's a realistic timeline, including permit review (60-90 days) and construction?
- Who is my point of contact and how are delays communicated?
- What warranty do you provide on workmanship?
- Can you share three recent Illinois ADU client references?
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