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Can You Build an ADU in Chicago?

ADU rules in Chicago are set by local zoning in Illinois. Many Illinois cities allow ADUs — here's what to check, plus typical costs ($183,000–$299,500 for a 700 sq ft detached unit).

Construction in Chicago runs about 8% above the Illinois average, so budget toward the higher end of these ranges.

Detached ADU (700 sq ft)

$183,000–$299,500

Garage conversion (400 sq ft)

$57,000–$104,500

Statewide protection

Local rules

What applies in Chicago

This state has no statewide by-right ADU law, so accessory dwelling units are governed entirely by your city or county zoning code. Many cities still allow ADUs — check your local planning department for size, setback and parking rules.

Check the Chicago planning or building department for ADU size, setback and parking rules before you design.

Estimate your Chicago ADU cost

Your property

ADU type

Estimated cost in Illinois

$183,000 – $299,500

≈ $261–$428/sq ft turnkey · midpoint $241,500

$164,200
Construction
$43,500
Design & permits
$33,800
Site work
ADU rules in Illinois are set by your city — here's what to check.
  • iSize set locally. This state leaves ADU size limits to your city — typical caps run 600–1,200 sq ft. Check your local code.
  • iParking. Set by local ordinance — commonly 1 space per ADU unless near transit.
  • iOwner-occupancy varies. Owner-occupancy rules are set locally in this state.
  • ✓Lot has room. A 700 sq ft ADU uses about 12% of your 6,000 sq ft lot — comfortably within typical coverage limits.

Rule basis: Local zoning governs — rules vary by city/county

If you rent it out

$1,175–$1,925

est. rent/mo

7.7%

gross yield

14 yrs

payback

~$17,298/yr after a 7% vacancy allowance, before financing & maintenance.

Financed over 20 yrs at 7.5%, the build is about $1,946/mo — vs ~$1,550/mo in estimated rent.

Get your detailed feasibility report →

Estimates are for planning only and are based on regional construction-cost indices and published statewide ADU statutes. Local ordinances, lot conditions and contractor pricing vary — always confirm with your city planning department and a licensed contractor.

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Other Illinois cities

AuroraNapervilleEvanstonSpringfield

Estimates are for planning only and are based on regional construction-cost indices and published statewide ADU statutes. Local ordinances, lot conditions and contractor pricing vary — always confirm with your city planning department and a licensed contractor.