Ill. Admin. Code tit. 77, § 870.100 – Site Location

a) The portion of the lot used for the placement of the manufactured home must be firm, undisturbed soil or compacted fill. The soil must be tested for its load-bearing capacity and graded to prevent surface water or drainage from accumulating under the home. For sites constructed after July 1, 2005, the ground must be sloped a minimum of ½ inch per foot for at least 6 feet from the perimeter of the home. Impervious surfaces such as concrete and asphalt in this area shall be sloped away from the home at least one inch per 6 feet.
b) All decayable material, such as grass, twigs, and wood scraps, shall be removed from under the home. Shrubs and overhanging branches that will impede installation in accordance with this Part shall be removed.
c) A minimum 6-mil visqueen vapor barrier, secured and extending to the dimensions of the home, must be placed on the ground underneath the manufactured home before the perimeter enclosure is installed, unless the home is placed on a poured concrete slab.
d) When gutters and downspouts are installed, the discharge shall be directed away from the home.