All driveways shall be of paving of a depth of not less than four inches and shall be at least eight feet in width. The driveway may be placed directly on compact and well-drained soil. Where soil is not well-drained, a four-inch sub-base of compact, clean, coarse gravel, sand or cinders shall be laid. The driveway shall slope not more than two inches per foot toward the roadway. The maximum driveway width at the curb line shall be ten feet.