Illinois residential building codes come from two places at once: state statutes that apply everywhere in Illinois, and local ordinances adopted by your city, village, or county. The state sets the floor for structural design, energy efficiency, smoke and carbon monoxide alarms, radon-resistant construction, and licensing for certain trades. Local building departments issue the permits, run the inspections, and decide when your project is done. Which specific rules govern your project depends on where the home sits and, in many areas, on what edition of the model code your local government has adopted.
What the State Code Covers and Where Local Rules Take Over
The Illinois Residential Building Code Act (815 ILCS 670) applies to new construction of single-family homes and dwellings with two or fewer apartments, condominiums, or townhouses.1Justia. Illinois Code 815 ILCS 670 – Illinois Residential Building Code Act Buildings with three or more units fall under separate commercial rules administered through local ordinances and the Capital Development Board Act.
Some parts of Illinois have no local building code at all. In those “non-building-code jurisdictions,” the Residential Building Code Act requires a new home construction contract to incorporate a residential building code chosen by the builder and buyer. They can pick the International Residential Code (IRC) or any municipal or county code in effect within 100 miles of the home. If they cannot agree, the IRC applies automatically, along with the Illinois Plumbing Code and the National Electrical Code.2Illinois General Assembly. Illinois Code 815 ILCS 670 – Illinois Residential Building Code Act
Where a municipality or county has adopted its own building code, that local code governs. But since January 1, 2025, every local code must regulate the structural design of residential buildings at least as stringently as the IRC. The statute defines the “baseline residential code” as the IRC edition published within the current or preceding nine calendar years with the least restrictive structural provisions.3Illinois General Assembly. Illinois Code 20 ILCS 3105 – Capital Development Board Act No local jurisdiction can drop below that floor.
The Illinois Accessibility Code is a common source of confusion. It covers public facilities, multi-story housing as defined by the Environmental Barriers Act, and residential facilities owned, leased, or financed by a governmental unit.4Capital Development Board. Building Codes and Regulations A private single-family home built without government financing is generally not subject to it. Multi-family projects with four or more units still face federal Fair Housing Act accessibility rules whether or not the state code applies.
Who Enforces These Codes
The Capital Development Board (CDB) is the state agency responsible for code policy. It recommends building codes to the General Assembly, publishes revisions, and maintains a public list of state codes together with each municipality’s adopted model code and local amendments.3Illinois General Assembly. Illinois Code 20 ILCS 3105 – Capital Development Board Act A municipality or county adopting a new code edition must report the model code title, edition, and any local amendments to the CDB at least 30 days before the code takes effect.
The CDB does not inspect your house. That work belongs to the local building department, which issues permits, sends inspectors, and handles violations. The Illinois Department of Public Health administers the state plumbing code and licenses plumbers.5Illinois Department of Public Health. Plumbing The Office of the State Fire Marshal oversees fire safety codes and smoke alarm requirements. For anything project-specific, start with your city, village, or county building department.4Capital Development Board. Building Codes and Regulations
Safety Rules That Apply Statewide
A handful of state laws set minimum safety requirements for homes regardless of which local code your municipality has adopted. These are the ones that most often surprise owners during renovations and resale.
Smoke Alarms
The Illinois Smoke Detector Act (425 ILCS 60) requires at least one working smoke alarm within 15 feet of every room used for sleeping. The alarm goes on the ceiling at least 6 inches from any wall, or on a wall between 4 and 6 inches from the ceiling. A single-family home needs at least one alarm on every story, including the basement.6Illinois General Assembly. Illinois Code 425 ILCS 60/3 – Smoke Detector Act In buildings with multiple units, the owner also installs an alarm at the uppermost ceiling of each interior stairwell.
For homes built, reconstructed, or substantially remodeled after December 31, 1987, the alarms must be hardwired to the AC power line, and alarms within a unit must be interconnected so triggering one activates all of them.6Illinois General Assembly. Illinois Code 425 ILCS 60/3 – Smoke Detector Act Since January 1, 2023, any new smoke alarm installed in a single- or multi-family home must use a 10-year sealed battery.7Office of the Illinois State Fire Marshal. Illinois Smoke Alarm Law
Carbon Monoxide Alarms
Under the Carbon Monoxide Alarm Detector Act (430 ILCS 135), every dwelling unit must have at least one working carbon monoxide alarm within 15 feet of every sleeping room. Battery-powered, plug-in with battery backup, or hardwired with battery backup units all qualify. Combined smoke and CO alarms are allowed as long as each hazard triggers a distinct alarm sound.8Illinois General Assembly. Illinois Code 430 ILCS 135 – Carbon Monoxide Alarm Detector Act
One exemption: a home does not need a CO alarm if it uses no fossil-fuel combustion for heat, ventilation, or hot water, is not connected to a garage, and is not close enough to any external CO source to be at risk, as determined by the local building commissioner.8Illinois General Assembly. Illinois Code 430 ILCS 135 – Carbon Monoxide Alarm Detector Act All-electric homes without attached garages usually qualify.
For both smoke and CO alarms, the building owner supplies and installs the devices. Tenants handle testing, general maintenance, and battery replacement in their units, but the owner must ensure batteries work at move-in and must provide written maintenance instructions.
Radon-Resistant Construction
All new residential construction in Illinois must include passive radon-resistant construction: a pipe system installed during building that uses natural air convection to vent soil gases from below the foundation up through the roof. A regular residential contractor or subcontractor can install the passive pipe, but only a licensed radon contractor can add a vent fan or upgrade the system to active mitigation.9Illinois General Assembly. Illinois Code 420 ILCS 52 – Radon Resistant Construction Act Local governments can impose stricter radon rules than the state baseline.
Energy Efficiency Rules
The Energy Efficient Building Act (20 ILCS 3125) directs the Capital Development Board to adopt an energy code that functions as both the minimum and the maximum standard for residential buildings across the state. Municipalities cannot set weaker requirements, and they cannot set stricter ones on their own unless they formally adopt the Illinois Stretch Energy Code.10Justia. Illinois Code 20 ILCS 3125 – Energy Efficient Building Act
The current Illinois Energy Conservation Code is based on the 2024 International Energy Conservation Code as amended, effective November 30, 2025.11Illinois Capital Development Board. Illinois Energy Conservation Code New homes and substantial renovations have to meet specific standards for insulation, window performance, HVAC efficiency, and air sealing.
The Stretch Energy Code is an opt-in path for municipalities that want tougher targets. By December 31, 2026, the CDB must adopt a stretch code with a residential site energy index no greater than 0.40 of the 2006 IECC baseline, with a potential relaxation to 0.42 if unanticipated burdens arise. A further tightening to 0.33 is due by December 31, 2029.10Justia. Illinois Code 20 ILCS 3125 – Energy Efficient Building Act Confirm with your local building department whether the stretch code is in effect where you are building; if it is, your energy targets are meaningfully tougher than the statewide baseline.
Licensed Trades That Affect Permits
Illinois has no single statewide general contractor license, but state licenses are required for trades that directly affect code compliance.
Roofing Contractors
The Roofing Industry Licensing Act (225 ILCS 335) requires anyone performing roofing work in Illinois to hold a state license. A limited license covers residential properties of eight units or fewer; an unlimited license covers residential, commercial, and industrial work. Applicants must carry liability insurance, workers’ compensation insurance, and a surety bond: $10,000 for a limited license, $25,000 for unlimited. A qualifying party at the company must pass an exam covering roofing practices and Illinois law.12Illinois General Assembly. Illinois Code 225 ILCS 335 – Roofing Industry Licensing Act
The contractor’s state roofing license number and name must appear on the building permit application and the issued permit. Roofing work can only be subcontracted to another licensed roofing contractor. Letting an unlicensed person use your license is a separate violation carrying fines up to $10,000 and license revocation.
Plumbers
The Illinois Plumbing License Law (225 ILCS 320) requires plumbers to be licensed through the Illinois Department of Public Health. Applicants must work as a licensed apprentice for at least four years, complete two years of high school or the equivalent, finish an approved training program, and pass a state exam. Plumbing contractors register with the state annually and carry general liability, bodily injury, property damage, and workers’ compensation insurance.5Illinois Department of Public Health. Plumbing Advertising plumbing services without displaying a valid license number is a Class A misdemeanor punishable by a $1,000 fine and license suspension or revocation.
Permits, Inspections, and the Certificate of Occupancy
Building permits are administered locally. Illinois has no statewide permit system; your city, village, or county building department is the issuing authority. Specifics vary, but the process is broadly the same everywhere: submit an application with architectural plans, pay a fee, wait for plan review, and receive the permit before breaking ground. Fees for new residential construction permits vary widely, from base fees as low as $65 in some areas to fee schedules that scale with construction value in others.
Inspections happen at set stages. Foundation, framing, rough plumbing and electrical, insulation, and a final inspection are typical checkpoints. The inspector verifies that the work matches the approved plans and meets applicable codes. If work fails, the deficiency has to be corrected before the project advances.
A certificate of occupancy is the finish line. In municipalities that require one, you cannot legally occupy a new home until all inspections pass and the certificate issues. Moving in before receiving it is treated as a code violation in most jurisdictions. Chicago, for example, requires applicants to pass all inspections, submit a formal application, pay outstanding inspection fees, and pick up the physical certificate before anyone occupies the building.13City of Chicago. Certificates of Occupancy
Penalties and Stop-Work Orders
Penalties depend on whether the violation sits under a local ordinance, a state licensing act, or both.
The Illinois Municipal Code lets municipalities impose fines up to $750 per offense for ordinance violations, including building code infractions, and treat violations as misdemeanors carrying up to six months of incarceration.14Illinois General Assembly. Illinois Code 65 ILCS 5 – Illinois Municipal Code Many municipalities count each day a violation continues as a separate offense, so fines accumulate quickly.
State licensing acts hit harder. Under the Roofing Industry Licensing Act, a first offense is a Class A misdemeanor (up to one year in jail and a fine up to $2,500). A second or subsequent offense is a Class 4 felony.12Illinois General Assembly. Illinois Code 225 ILCS 335 – Roofing Industry Licensing Act Contractors also face license suspension or revocation for code violations, and local ordinances may add grounds for revocation beyond what state law requires.
Local building inspectors can issue stop-work orders that halt construction immediately. Work cannot resume without the inspector’s written permission. Courts can order buildings brought into compliance, or demolished at the owner’s expense, for dangerous or abandoned structures.
Variances and Flexibility for Historic Buildings
Strict code compliance is sometimes impossible because of the physical characteristics of a property. A variance allows a deviation, but the bar is high. A zoning board looks for evidence that the property cannot yield a reasonable return under existing regulations, that the difficulty stems from circumstances unique to the property and not self-created, and that the variance will not alter the essential character of the surrounding area.15City of El Paso. Variance Guidelines and Criteria Applicants file detailed plans and justifications, and most municipalities hold a public hearing before the board votes. The standard is “practical difficulty or particular hardship” tied to the specific property. Wanting to build bigger or cheaper is not enough.
Historic properties get real flexibility through the Illinois Existing Building Code, which incorporates Chapter 12 on historic buildings. Repairs can use original materials and construction methods rather than modern code-compliant alternatives. Existing stairway widths, door openings, and corridor dimensions can remain if the code official determines they provide adequate passage. Grand stairways are exempt from current handrail and guard requirements, and one-hour fire-resistance ratings are waived where existing walls and ceilings use wood or metal lath and plaster. A historic building undergoing a change of use can exceed the normally allowable floor area by 20 percent. The code official keeps discretion over life safety, but the framework is deliberately more permissive than the rules for new construction.