What Illinois Code Says About Dryer Vents
Illinois adopts the International Residential Code (IRC) with state-specific amendments, and that code contains clear requirements for clothes dryer exhaust systems. For most Bloomington homeowners, these requirements matter most when a dryer vent is being installed or replaced — and when a professional inspection reveals that an existing installation is out of compliance.
Duct Material Requirements
The IRC requires that dryer exhaust ducts be constructed of rigid metal — either galvanized steel or aluminum — with a minimum thickness of 0.016 inches. Flexible metal transition duct may be used for the short section connecting the dryer to the rigid duct system, but it must not be concealed within walls, floors, or ceilings. Flexible plastic or foil duct — the lightweight accordion-style material sometimes found in older homes — does not meet current code for dryer exhaust and represents a fire hazard that should be replaced.
Maximum Duct Length
The IRC limits dryer exhaust duct length based on the number and type of bends. The baseline maximum for smooth rigid metal duct is 35 feet of equivalent length. Each 90-degree elbow reduces the allowable total by 5 feet; each 45-degree elbow reduces it by 2.5 feet. This means a duct with two 90-degree bends can be no longer than 25 feet. These limits exist because longer runs cannot exhaust air effectively and create lint accumulation conditions that compromise safety and performance.
If your home's dryer is located far from an exterior wall and your duct exceeds these limits, a booster fan can be installed to improve airflow and bring the effective duct performance into an acceptable range. A professional inspection can evaluate whether your duct length is within code parameters.
Exterior Termination Requirements
Dryer exhaust must terminate on the exterior of the building — not into attic spaces, crawl spaces, wall cavities, or garages. The exterior cap must be equipped with a backdraft damper (the flap mechanism) and must not be installed with a mesh screen, which catches lint and creates blockages. The cap must be positioned to prevent moisture, rain, and pests from entering the duct.
Why Code Compliance Matters for Existing Homes
Most code requirements only apply to new installations — if your home was built decades ago with flexible foil duct, you are not automatically required to upgrade. But understanding these standards helps you make informed decisions. A professional dryer vent inspection can evaluate your system against current standards and explain what, if anything, should be considered for upgrade. Contact our Bloomington team for a complete inspection.
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