ADU Rules in Chicago, IL (2026)

Chicago, IL permits accessory dwelling units (ADUs) on residential properties. ADUs — also called granny flats, in-law units, backyard cottages, or secondary suites — are secondary housing units on a single-family or multifamily lot. State and local law governs the approval process. In Chicago, the Chicago Department of Buildings handles ADU permit applications. Below you will find the current size limits, setbacks, fees, and timeline for building an ADU in Chicago.

ADU Size Limits

ADU Size Limits in Chicago: Detached ADU: size varies by zoning — see official source (max height: varies — see official source). Attached ADU: size varies by zoning — see official source.

Permit Fees

ADU Permit Fees in Chicago: Plan check fee: $200–$1,500. Building permit fee: Based on construction value — typically $1,000–$5,000. Impact fees: None. School fees: None or N/A. Total estimated permit cost: Varies.

Permit Timeline

Chicago ADU Permit Timeline: Chicago DPD building permit for ADU: typically 3-6 months for plan review. ADU Express program in development. Construction 4-12 months. Apply through the Chicago Department of Buildings online permit portal. Phone: (312) 744-5000.

Setback Requirements

ADU Setback Requirements in Chicago: Front setback: follows zone standard. Side setback: no minimum. Rear setback: no minimum.

Parking Requirements

Parking Requirements: No replacement parking required when garage is converted to ADU. New detached ADUs (coach houses) typically built over new 1-car garage — no additional parking required per ADU Ordinance.

Restrictions & Requirements

• •Owner-occupancy required — must reside on property
• •Annual owner-occupancy affidavit required
• •ADU must comply with Chicago Building Code habitability standards
• •Basement conversions must meet minimum ceiling height (7 ft habitable space minimum)
• •Only one ADU per lot (principal building, not counting multi-unit buildings)
• •Chicago Affordable Requirements Ordinance (ARO) may apply in certain areas
• •Landmark or contributing structure in landmark district requires additional review

How Many ADUs Are Allowed?

Number of ADUs Allowed in Chicago: Single-family lots: 1 ADU per lot. Multifamily properties: Existing 2-flats and larger multifamily have different rules — conversion of existing units vs. new ADU construction. Chicago ADU Ordinance Phase 1 (2021) covered 5 pilot areas. Phase 2 (2022) expanded to entire city. Both attached (basement/attic) and detached (coach house) ADUs permitted citywide.

Single-Family Lots

1 ADU per lot

Multifamily Properties

Existing 2-flats and larger multifamily have different rules — conversion of existing units vs. new ADU construction

Statewide Preemption

Historic District Considerations

Frequently Asked Questions