ADU Construction permits in Illinois
What Illinois building departments require for adu construction, what it adds to a $159,000 – $318,000 project, and how the rules differ across 12 cities we track in the state.
The Illinois permit process, step by step
Confirm whether your scope is permitted work
In Illinois, structural, electrical, plumbing, mechanical and most exterior envelope work on adu construction projects triggers a permit. Cosmetic, like-for-like repairs often do not.
Let the licensed contractor pull it
A contractor who asks you to pull an owner-builder permit is shifting liability to you. Whoever pulls the permit is responsible for code compliance.
Budget for fees and plan review
Permit fees are usually a percentage of job valuation plus a flat plan-review fee. On a typical Illinois adu construction project of $159,000 – $318,000, expect permitting to be a low single-digit percentage of the total.
Schedule inspections before you close things up
Rough-in inspections have to happen before drywall, backfill or roofing covers the work. A missed inspection can mean tearing finished work back out.
Keep the final sign-off
The closed permit and certificate of completion belong in your home file — buyers, appraisers and insurers all ask for them on permitted work.
City-by-city permit notes
| City | Local permit note | Typical project |
|---|---|---|
| Chicago | City permits, licensed-contractor registration and inspections are strictly enforced. | $171,000 – $342,000 |
| Aurora | City permits required for exterior and structural work. | $159,000 – $318,000 |
| Naperville | City permits plus HOA architectural review are common. | $168,000 – $336,000 |
| Joliet | City permits apply to structural and exterior projects. | $156,000 – $312,000 |
| Rockford | Most Rockford, IL projects that change structure, electrical, plumbing or mechanical systems need a permit from the local building department; cosmetic work usually does not. | $151,500 – $303,000 |
| Elgin | City permits required for roofing and structural work. | $157,500 – $315,000 |
| Springfield | Most Springfield, IL projects that change structure, electrical, plumbing or mechanical systems need a permit from the local building department; cosmetic work usually does not. | $150,000 – $300,000 |
| Peoria | Most Peoria, IL projects that change structure, electrical, plumbing or mechanical systems need a permit from the local building department; cosmetic work usually does not. | $150,000 – $300,000 |
| Champaign | Most Champaign, IL projects that change structure, electrical, plumbing or mechanical systems need a permit from the local building department; cosmetic work usually does not. | $154,500 – $309,000 |
| Cicero | Town permits and licensed-contractor requirements apply. | $160,500 – $321,000 |
| Evanston | City permits with historic preservation review in many blocks. | $174,000 – $348,000 |
| Schaumburg | Village permits required for most remodels and exterior work. | $163,500 – $327,000 |
ADU Construction permit FAQs for Illinois
Permit requirements are set locally and change. Confirm details with your city or county building department before starting work. Typical statewide project value used here: $238,500.