St. Clair County, IL Noise Ordinances: Aircraft Noise (2026)

Sec. 40-4-128 sets up four aircraft noise contour zones measured in day-night average sound level (DNL): NZ-1 runs 65 to 69 dB, NZ-2 runs 70 to 74 dB, NZ-3 runs 75 to 79 dB, and NZ-4 exceeds 80 dB, though NZ-4 is "only located on federally controlled land," meaning Scott AFB property rather than private parcels. Sec. 40-4-130 layers use and construction restrictions on top of the underlying zoning district for each zone: manufactured housing and outdoor amphitheaters are barred in every noise zone, and NZ-2 through NZ-4 additionally prohibit new residential uses, hotels and overnight lodging outright, with NZ-3 and NZ-4 also barring hospitals, nursing homes, child care centers, schools, theaters and churches.

Where a noise-sensitive building is still permitted, Sec. 40-4-130 requires sound attenuation reaching a 25 dB noise reduction level (NRL) in NZ-1 and a 30 dB NRL in NZ-2 through NZ-4 for offices, retail and industrial space, and 25-30 dB for hospitals, schools and similar uses depending on the zone. Sec. 40-4-131 spells out how that attenuation is achieved: plans must be certified by a recognized acoustical specialist, and buildings must use sealed, close-fitting doors and windows, capped chimneys, bent ventilation ducts, and caulked wall penetrations so no direct line of sight to the outdoors exists through any vent.

Existing homes are grandfathered for additions and repairs if the owner signs a waiver acknowledging the specifications were not applied. Development applications within the AO-4 District also require Air Force consultation under Sec. 40-4-115.