Illinois Building Codes: Local Adoption, No Statewide Residential Edition

Illinois has no single statewide IRC edition for residential construction. Local jurisdictions adopt their own edition, and Illinois Public Act 103-0510 (effective 1 January 2025) only sets a floor — a local residential code must be at least as stringent as the current or immediately preceding IRC edition — without mandating a specific one. Chicago is the standout case: the city runs its own Chicago Building Code, authored and administered separately from any statewide code, rather than a straight IRC adoption.

Because the operative edition is set locally, there’s no single “Illinois” figure for stair or guard geometry to cite here. Outside Chicago, most jurisdictions build from something close to the IRC baseline — 7¾ in max riser, 10 in min tread, 6 ft 8 in headroom, 36 in min width, 34–38 in handrails, 36 in guards, the 30 in guard trigger and the 4 in sphere (see the US stair & guard rules) — but Chicago’s own code may differ, and any jurisdiction may have amended. Confirm the adopted edition and any amendments with your local building department.