Can You Turn a Basement Into a Legal Apartment in Chicago?

Converting a basement into a legal apartment has become a realistic option for many Chicago homeowners thanks to Chicago's expanded ADU ordinance. The April 2026 ordinance has changed things for Chicagoans. In September 2025, after a 70-year ban, the Chicago City Council voted to legalize accessory dwelling units (ADUs) citywide. The expanded ordinance took effect on April 1, 2026.

The new regulation opens up roughly 60% of Chicago’s residential areas to basement conversions, coach houses, and attic units for the first time since 1957.

You can legally convert a basement into an apartment in Chicago, but it depends on a few factors:

• Does your specific property qualify?
• Can your basement meet the building code?

The hidden requirements can surprise even experienced homeowners, house hackers, and investors. This guide walks you through all of it with the updated 2026 rules.

Quick Check: Is Your Basement a Good Candidate?

Before diving into permits and building codes, here's a quick way to determine whether your basement is a good candidate for conversion.

• Your building is at least 20 years old.
• Your basement has a ceiling height of around 7 feet after finishing*.
• You haven't had recurring water or drainage problems.
• There's enough floor space to create a livable unit with a kitchen, bathroom, and sleeping area.

*For basement ceiling height, there are exceptions. All habitable rooms (bedrooms, living rooms, and kitchens) must have a minimum finished ceiling height of 7 feet. A lower minimum ceiling height of 6 feet 8 inches is allowed for non-habitable spaces such as bathrooms, laundry rooms, and hallways.

Issues with ceiling height or water problems can prevent a basement conversion project from starting before anything else.

What is a Garden Unit in Chicago?

A garden unit in Chicago is a basement-level apartment with a specific physical characteristic:

• The floor is partially below grade (below ground level), but not fully underground
• Windows are partially above ground, often at sidewalk level
• Usually gets some natural light, but not as much as upper floors

Many non-conforming or illegal garden units exist in Chicago and it’s important to address any code violations or safety issues.

What Counts as a Legal Basement Apartment?

An ADU (accessory dwelling unit) is a secondary residential unit on the same lot as a primary home. The city recognizes two main types:

• An attached unit: It could be created inside an existing building, such as converting a basement or attic space into a living area.
• A coach House: It’s a separate, detached structure in the backyard. The rules for coach houses are more complex (and more expensive). So this is the simpler category if you are thinking about a basement conversion.

Is Your Property Eligible?

Not every property in Chicago qualifies for an ADU. Properties in multifamily zoning districts are generally allowed to add ADUs by right across the city. Properties in single-family residential zones (RS districts) outside the original five pilot areas depend on whether your alder person has opted into the program for your ward. Many wards have opted in, but rules change frequently.

Before you do anything else, check your address at chicago.gov/adu or use the Chicago Cityscape mapping tool to confirm your zoning district and eligibility status.

Building Age

Your building must be at least 20 years old to add a conversion unit. This rule prevents owners of newly constructed properties from building an additional unit. Most Chicago homeowners, especially those in bungalows, two-flats, and greystones, will not face this issue.

How Many Units You Already Have

If your property has one to four existing legal units, you can add one conversion unit or one coach house. If your property has five or more units, coach houses are off the table, but you can add attached units equal to up to 33 percent of your existing legal unit count.

Owner-Occupancy Rules

If you own a single-family home or a two-flat, you must live on the property. Owners of buildings with three or more units are not subject to this requirement. Real estate investors must consider this situation to determine whether adding another unit makes financial sense.

Building Requirements: Can Your Basement Meet Code?

Even if your local ward allows an ADU, your basement must meet Chicago’s building code standards. These are the requirements that determine whether a conversion is actually feasible.

Ceiling Height: The Biggest Hurdle

The Chicago building code generally requires 7 feet of height in a habitable area, though limited exceptions may apply for existing structures. The measurement must be taken from the finished ceiling and not from the floor joists above. Once you account for drywall, dropped ceilings, ductwork, and beam protrusions, many basements that seem to have enough clearance fall short.

If your basement can't reach 7' after finishing, the project is generally not viable without excavating the floor, which is a major, expensive undertaking. This is the single most common reason basement conversions in Chicago don't move forward, and it's the first thing any architect or contractor will assess.

Egress

Every basement unit needs egress, which is a way for occupants to escape in an emergency. That means every bedroom in a basement must have egress windows.

If your basement already has large enough windows to meet code, that’s a significant advantage. But if windows don’t exist, you will need to cut new openings into the foundation wall and install window wells. This is doable in most circumstances, but it will increase project cost.

Moisture and Waterproofing

If you want to convert a basement into an apartment, the walls and floors must be waterproofed. Waterproofing should be addressed before investing in architectural plans or permits. Any existing water problems must be remediated before any inspection will pass. The cost of waterproofing can often surprise homeowners.

Ventilation and Safety Systems

The newly converted apartment unit must have proper airflow and insulation and may require upgraded utilities (or separate utilities depending on layout and compliance). Smoke detectors and carbon monoxide detectors are required in every unit. There must be fire-rated separations (walls, ceilings, and doors) between the basement unit and the rest of the building.

When a Basement Conversion May Not Be Worth It

A basement conversion is usually not worth pursuing if:

• The ceiling height cannot reach 7 feet without expensive excavation.
• There is a persistent water or drainage problem that would cost more to fix compared to the potential ROI.
• The ward or zoning classification makes the project impractical.

The Permit and Approval Process

Step 1: Check eligibility. Use chicago.gov/adu or Chicago Cityscape to confirm your zoning district and whether ADUs are permitted on your property.

Step 2: Get DOH pre-certification. Apply to the Chicago Department of Housing for pre-certification that your project is permissible under the ADU ordinance.

Step 3: Hire an architect. You'll need architectural drawings showing how your unit meets all building code standards. The Department of Buildings requires plans before it will issue a permit.

Step 4: Submit your permit application. Take your pre-certification letter and architectural plans to the Chicago Department of Buildings.

Step 5: Build and inspect. After receiving permits, you can begin construction. Once the project is complete, it will need to undergo a city inspection before a certificate of occupancy is issued.

What Does It Cost to Convert a Basement Into a Legal Apartment?

Costs vary considerably depending on the condition of your basement and the amount of work required to bring it into compliance.

The typical fee for a permit ranges between $500 and $5,000 depending on the project scope. Architectural design is an additional cost layer and can fall between $5,000 and $15,000. For a basement conversion, ceiling adjustments, egress window cuts, waterproofing, electrical panel upgrades, and plumbing rerouting are the main cost drivers.

Typical Timeline

Plan review and permitting can take 2-4 months depending on the complexity of your project and current city department workloads. Construction for a basement conversion unit can take several months. Expect the process to take 4-10 months and build in a buffer for the unexpected.

Renting Out Your Basement: What to Know

Many homeowners plan a basement conversion to earn additional income. The rent for a basement apartment can vary considerably by neighborhood. In some areas of the South Side, you can expect to earn $1,000-$1,200 per month. But in the North Side, for neighborhoods like Logan Square, Lincoln Square, or Andersonville, the rents can be $1,800-$2,200 or more per month.

For example, if you are investing $120,000 and expect to get a monthly rent of $1,800, your gross rent would be $21,600 with a typical payback of 6-10 years.

That said, there are a few things every owner needs to understand.

• Rental income is taxable. Your property taxes will also likely increase once the city reassesses your property with an additional unit. Consult a tax professional before your first tenant signs a lease.
• Short-term rentals are not allowed. ADUs created under this ordinance must be used for long-term housing only.
• For properties with two or more ADUs, there can be another challenge. If you receive financial assistance, affordability requirements may apply. You might have to rent a portion of those units at rates affordable to low-income households. You don’t have to worry about it if you are planning a single basement conversion but it’s worth knowing if you are considering multiple units.

How to Legalize an Existing Basement Apartment

Unpermitted basement apartments are extremely common across Chicago. The 2026 ADU ordinance now creates a clear pathway to legalize those units. The first step is to apply for a building permit and hire an architect to produce plans showing how the unit meets the current code. Once the city inspection is passed, the unit will receive a certificate.

The process takes time and money but a legalized unit provides several benefits. You and your tenants will have legal protection. You will avoid penalties and the property becomes easier to sell.

Frequently Asked Questions

Can you legally convert a basement into an apartment in Chicago?

Yes. As of April 1, 2026, Chicago's expanded ADU ordinance allows basement conversions in most residential zones across the city. Your property and basement meet specific eligibility and code requirements.

What is the minimum ceiling height for a basement apartment?

The minimum required height is 7 feet throughout all habitable space, and it’s measured from the finished ceiling to the finished floor.

Do you need to live on the property?

Yes, for one- or two-unit buildings, the owner must live on the property.

Can you use a basement ADU for Airbnb?

No. Units created under the ADU ordinance must be used for long-term rentals only. You cannot rent the house for less than 30 days.

Does the building need to be 20 years old?

Yes. All basement conversion units require the existing building to be at least 20 years old.

Do you need to add a parking space?

No. Chicago's ADU ordinance explicitly does not require additional parking when adding an ADU.

Will property taxes increase?

Likely yes. Adding a legal rentable unit increases your property's assessed value as an income-producing asset. Please consult a tax professional about your specific situation.

How do I convert my non-conforming garden unit into a legal, conforming garden unit?

Making a garden unit legal involves securing permits, ensuring proper ceiling height, light, ventilation, and emergency exits (egress), addressing moisture and fire safety issues, and confirming that zoning allows an additional dwelling unit.

About Quality Builders

Quality Builders specializes in residential renovations throughout the Chicago area, helping homeowners and real estate investors transform their properties with confidence. From planning and permitting to construction and project completion, our team combines decades of experience with a transparent, process-driven approach to deliver exceptional results.

Whether you're considering a basement conversion, ADU, home addition, kitchen remodel, or whole-home renovation, we're here to help you understand your options and make informed decisions before construction begins.