Cook County adopts the Illinois Energy Conservation Code statewide minimum and supplements it with the Cook County Sustainable Building Ordinance for county-owned projects, while many suburbs require LEED, Energy Star, or stretch energy code compliance for private development.
Illinois preempts local energy codes through the Energy Efficient Building Act (20 ILCS 3125), mandating a uniform statewide energy code based on the IECC. Cook County's Sustainable Building Ordinance applies LEED Silver or equivalent to county-funded buildings over 10,000 square feet. Several suburban Cook municipalities (Evanston, Oak Park, Highland Park) have adopted climate action plans requiring private-sector benchmarking, electrification incentives, or green roofs. Chicago has its own Energy Transformation Code. New residential construction must meet IECC 2021 envelope, lighting, and HVAC requirements, verified through blower-door and duct-leakage testing.
Failing IECC envelope or duct-leakage testing prevents certificate of occupancy. Missing benchmarking deadlines in opt-in suburbs triggers escalating administrative fines under local sustainability ordinances.
See how Oak Park's green building code rules stack up against other locations.
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