In Illinois, most adu projects cost between $50,000 and $200,000 per job, with a typical price near $100,000. Local labour, permits and materials move the final price, so treat the range below as a planning guide.
Typical adu cost
$50,000 – $200,000
per job · typical $100,000
A general planning range, not a quotation.
Adu cost breakdown
- Garage conversion$30,000 – $80,000typical $50,000
- Attached ADU (addition)$80,000 – $200,000typical $120,000
- Detached ADU (new build)$100,000 – $300,000typical $180,000
At a glance
- Typical range$50,000 – $200,000
- Unitper job
- Cities covered50
What ADUs costs
Costs cover design, permits, construction, and utilities for adding a separate living unit on your property. Detached units are pricier than attached or garage conversions. Local regulations and site conditions significantly affect price.
By city in Illinois
- Addison
- Alton
- Arlington Heights
- Belleville
- Berwyn
- Bolingbrook
- Buffalo Grove
- Calumet City
- Carbondale
- Carol Stream
- Carpentersville
- Champaign
- Chicago
- Cicero
- Crystal Lake
- DeKalb
- Decatur
- Des Plaines
- Downers Grove
- Elgin
- Elmhurst
- Evanston
- Glenview
- Hanover Park
- Hoffman Estates
- Joliet
- Kankakee
- Lombard
- Moline
- Mount Prospect
- Naperville
- Normal
- Oak Lawn
- Oak Park
- Orland Park
- Palatine
- Park Ridge
- Peoria
- Rock Island
- Rockford
- Romeoville
- Round Lake Beach
- Schaumburg
- Skokie
- Springfield
- Streamwood
- Tinley Park
- Urbana
- Waukegan
- Wheaton
Frequently asked questions
How much does an ADU cost on average?
Nationally, $100,000–$200,000 for a typical 600-1,200 sq ft unit. Garage conversions may cost less, while high-end detached units exceed $250,000.
What drives ADU costs?
Size, type (attached/detached), foundation, plumbing/electrical runs, and local permit fees. Site conditions like sloping land or need for a new sewer line increase costs.
How can I save on ADU construction?
Use prefabricated units, convert existing space, shop for contractors, and finance with a HELOC or construction loan. Check for local grants or incentives for ADUs.