Where building sites are graded into generally horizontal planes, and where the difference in elevation between contiguous building sites is greater than three feet (3'), the required side yard at the toe of the slope shall be increased by one foot (1') for each foot, or portion thereof, over three feet (3') of elevation differential. In no case may any building or structure be closer than three feet (3') from the toe of the slope in such side yard, so as to provide for drainage away from the building. (Ord. 1000 § 38.00(B), 1955)