All mobile homes shall be placed and leveled on stands consisting of a 16-inch by 16-inch by 4-inch deep square solid base, minimum, with a double tier of alternately crossed 8-inch block ascending; no I-beam or any portion of the mobile home frame shall rest directly on the concrete block. Wood shimming shall be used. No second or medium grade of concrete block may be used and all block must be installed with the hollow core in a vertical position. These stands shall be placed with a minimum spacing of eight feet.