ADU rules in Illinois
Representative cities: Chicago, Springfield.
ADU permit rule
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Frequently asked questions
Do I need a permit to build an ADU in Illinois?
Per Illinois rules, an ADU is "yes" for a permit and the authority is "city". Illinois has no statewide building code; most municipalities use the IRC while Chicago enforces the 2019 Chicago Building Code. ADUs require a building permit plus local zoning approval — Chicago and other cities regulate ADUs through zoning. Verify with your municipality. Always confirm with the issuing building department.
How big can an ADU be in Illinois?
Size limits for an ADU in Illinois are set by local zoning — verify with your city building department.
What are the ADU setbacks in Illinois?
Setback rules vary by city in Illinois; confirm with the local planning or building department.
How much does an ADU permit cost in Illinois?
Fee basis: No flat statewide fee; Chicago calculates fees from construction type, occupancy, square footage, and scope via its online calculator. Other municipalities set their own fees.