20 ILCS 3125/15
The Board, in consultation with the Agency, shall adopt the Code as minimum requirements for commercial buildings, applying to the construction of, renovations to, and additions to all commercial buildings in the State. The Board, in consultation with the Agency, shall also adopt the Code as the minimum and maximum requirements for residential buildings, applying to the construction of, renovations to, and additions to all residential buildings in the State, except as provided for in Section 45 of this Act. The Board may appropriately adapt the International Energy Conservation Code to apply to the particular economy, population distribution, geography, and climate of the State and construction therein, consistent with the public policy objectives of this Act.
20 ILCS 3125/15