Thinking about a home addition? Chicago’s ADU Ordinance Takes Effect April 1, 2026 — Here’s What Homeowners Need to Know
Starting April 1, 2026, Chicago’s permanent Accessory Dwelling Unit (ADU) ordinance goes into effect — and it’s a game-changer for homeowners across the city. After a nearly 70-year ban on coach houses and secondary dwelling units, the Chicago City Council voted 46-0 in September 2025 to legalize ADUs citywide. Whether you’re thinking about building a coach house in your backyard, converting your basement into a rental unit, or creating space for aging parents, this guide breaks down everything you need to know.
What Is an ADU?
An Accessory Dwelling Unit (ADU) is a secondary residential unit on a single property. Chicago’s ordinance recognizes two types:
- Coach House: A detached structure in your rear yard — typically a dwelling unit above or beside a garage. These are the classic Chicago coach houses that were common before the 1957 ban.
- Conversion Unit: A unit created inside your existing building — think basement apartments, attic conversions, or repurposed interior space. Your building must be at least 20 years old to qualify for a conversion unit.
Important: You cannot build both a coach house AND a conversion unit on the same property. You have to pick one.
Where Are ADUs Allowed?
The new ordinance significantly expands where ADUs can be built compared to the original pilot program, which only covered about 12% of Chicago. Here’s how it breaks down by zoning district:
- RT (two-flat/townhouse) and RM (multi-family) districts: ADUs are allowed citywide, by right. No aldermanic approval needed.
- RS (single-family) districts within the original five Pilot Areas (North, Northwest, West, South, Southeast): ADUs continue to be allowed.
- RS districts outside the Pilot Areas: Your alderperson must opt in your area. As of late 2025, 28 wards have opted in, but the rules vary by ward.
- Downtown zoning districts: ADUs are not permitted.
This is where it gets tricky: each alderperson can set their own restrictions for RS zones in their ward, including owner-occupancy requirements, caps on permits per block per year, and whether an administrative adjustment (a $500 application) is required. The rules can literally vary from one block to the next. Check your eligibility at
chicago.gov/adu or use
Chicago Cityscape to look up your zoning district.
How Many ADUs Can You Add?
- Properties with 1–4 existing units: You can add one coach house OR one conversion unit (building must be 20+ years old for conversion units).
- Properties with 5+ units: No coach houses allowed, but you can add conversion units equal to up to 33% of your existing legal units.
In some RS zones (South, West, and Southeast Pilot Areas), there are also block-level caps: one ADU permit per block per year in RS-1, two in RS-2, and three in RS-3 zones.
Key Rules You Need to Know
Coach House Size and Height Limits
Coach house floor area is limited to 60% of your property’s required rear setback. On a standard Chicago lot, this works out to roughly 450 square feet. The height cap is 22 feet to the top of the highest feature. Larger lots can accommodate larger structures.
No Short-Term Rentals
ADUs built under this ordinance
cannot be used for Airbnb, VRBO, or any rental shorter than 30 days. They must be long-term rental units or family housing. Violating this can result in fines and permit revocation.
Apprenticeship Requirement for Coach Houses
This is a big one that catches many homeowners off guard: any contractor building a coach house must participate in a federally Registered Apprenticeship Program (RAP) approved by the U.S. Department of Labor. As of late 2025, only about 24 companies in Chicago meet this requirement. This limits your contractor options and can affect pricing. There are no exceptions. This requirement does
not apply to conversion units (basement/attic conversions).
Owner Occupancy
In the West, South, and Southeast Pilot Areas, owner occupancy is required when adding an ADU to a property with 1–3 units. Other areas may or may not have this requirement depending on what your alderperson has decided.
Affordability Requirements
If your property will contain two or more ADUs, affordability rules apply. 50% of the ADU units (rounded down) must be rented at rates affordable to households earning 60% of the area median income.
Legalizing Existing Units
The ordinance also creates a pathway to legalize existing unpermitted units — those basement apartments or attic units that were built without proper zoning approval. You’ll need to apply for a building permit with architectural plans showing the unit meets current building code. The unit will be inspected and must be brought up to code.
What Does an ADU Cost to Build in Chicago?
Let’s talk real numbers. ADU costs vary significantly depending on whether you’re building new or converting existing space.
Coach House (New Construction)
Total costs typically range from $150,000 to $350,000+, depending on design and finishes. On a per-square-foot basis:
- Budget builds: $200–$280 per square foot
- Mid-range: $280–$400 per square foot
- High-end: $400–$500+ per square foot
For a typical 450–600 square foot unit, most homeowners should expect to pay $175,000–$250,000 all-in. Early adopters in the pilot program have reported costs around $300,000, and the apprenticeship requirement may push those numbers higher by limiting contractor competition.
Keep in mind that most existing Chicago garages were not built to support a second floor — the foundation and framing typically can’t handle the load. In many cases, you’ll need to demolish the existing garage and build new, or significantly reinforce the structure.
Basement/Attic Conversion Unit
Conversion units are generally more affordable since you’re working within an existing structure:
- Basement conversion (existing rough-in): $65,000–$90,000
- Full basement ADU conversion: $90,000–$120,000+
- Cost per square foot: $130–$250
These costs include a full kitchen, bathroom, separate entrance, egress windows, waterproofing, and all Chicago permits. With garden-unit rents averaging $1,200–$2,200/month across Chicago neighborhoods, most owners recoup their investment in 4–7 years through rental income.
Permit Costs
Budget $14,000–$26,000 for permits and associated fees. ADU permits currently take an average of 121 days to process — longer than standard permits due to additional review requirements. The process involves multiple city departments including the Department of Housing, Department of Planning and Development, and Department of Buildings.
The Permit Process: Step by Step
- Check eligibility: Confirm your property is in an eligible zoning district. Use chicago.gov/adu or Chicago Cityscape.
- Apply for ADU pre-approval: Submit your application to the Chicago Department of Housing with property information, unit count, and neighbor notification proof. This confirms eligibility but does not authorize construction.
- Hire an Illinois-licensed architect: All ADU plans must be prepared by a licensed architect. Plans must show code-compliant layouts including egress windows, ceiling heights, separate entrance, kitchen, bathroom, and mechanical systems.
- Submit building permit application: File architectural plans with the Chicago Department of Buildings. Processing currently averages about 4 months.
- Administrative adjustment (if required): Some wards require this additional step, which involves a $500 fee and documentation showing your project meets specific zoning criteria.
- Begin construction: Once all approvals are in hand, construction can start. Budget 4–10 months for construction depending on scope.
Permit applications for the new ordinance can be submitted starting April 1, 2026. If you’re in an existing pilot zone, you can move forward now under current rules.
Is an ADU Worth It? Financial Considerations
Beyond rental income, a legally permitted ADU can significantly increase your property’s assessed value. Homeowners who add a coach house may qualify for the
Home Improvement Exemption, which can shield a portion of the added value from property tax reassessment for up to four years.
However, the numbers need to make sense for your specific situation. Here are some factors to weigh:
- Rental income potential: Garden-unit and basement apartment rents vary by neighborhood — from $1,200/month in some South Side areas to $2,200+ in North Side neighborhoods.
- Property value increase: A legal rental unit can increase your property’s valuation as an income-producing asset, often exceeding the cost of the conversion.
- Tax implications: Consult a tax professional — ADU rental income is taxable, and your property taxes will likely increase.
- Financing: Home equity loans, HELOCs, and construction loans are common financing options. Some homeowners use cash-out refinancing.
Tips for Chicago Homeowners Considering an ADU
- Know your ward. Research what your alderperson has decided about ADUs in your specific area. Rules vary enormously across Chicago’s 50 wards.
- Start planning now. Even though permits can’t be submitted until April 1, you can begin working with an architect, lining up financing, and checking eligibility today.
- Budget realistically. Build in a 10–15% contingency for unexpected costs. Older structures often reveal surprises once construction begins.
- Choose the right contractor. For coach houses, your contractor must participate in a Registered Apprenticeship Program — verify this before signing any contract. For conversion units, this requirement doesn’t apply, giving you a wider pool of contractors.
- Talk to your neighbors. The permit process requires neighbor notification. In Chicago, neighbor pushback can become political quickly. A conversation upfront can save headaches later.
- Think long-term. Interior conversions can be less expensive than a new coach house, but both require real money and a long-term view. Run the ROI numbers like an investor.
- Don’t skip the architect. Chicago requires an Illinois-licensed architect for all ADU plans. Cutting corners on design leads to permit delays and code violations.
How Bofran Builders Can Help
At
Bofran Builders, we’ve been doing general construction in Chicago and the surrounding suburbs since 1999. We understand Chicago’s permitting process, building codes, and the unique challenges of working on Chicago lots. Whether you’re considering a basement conversion, attic buildout, or a new coach house, we can help you evaluate your options, navigate the permit process, and build a code-compliant ADU that adds real value to your property.
Contact us for a free consultation to discuss your ADU project.
Frequently Asked Questions
When does the new Chicago ADU ordinance take effect?
April 1, 2026. That’s also the first day permit applications will be accepted for areas outside the original pilot zones.
Can I use my ADU as an Airbnb?
No. ADUs built under this ordinance must be used for long-term housing only. No short-term rentals under 30 days. Violating this can result in fines and permit revocation.
How much does it cost to build a coach house in Chicago?
Expect $150,000–$350,000+ for a new coach house, or $200–$400+ per square foot. Basement conversions are more affordable at $65,000–$120,000.
Do I need to live on the property to build an ADU?
It depends on your location. Owner occupancy is required in some areas (West, South, and Southeast Pilot Areas for properties with 1–3 units) but not others. Check with your ward office.
Can I build an ADU on any property in Chicago?
Not yet. RT and RM zoning districts are eligible citywide. RS (single-family) zones require your alderperson to opt in. Downtown areas are excluded entirely.
How long does the ADU permit process take?
Plan for 4–6 months from application to permit approval, plus 4–10 months of construction. ADU permits currently average 121 days to process.
