“Story” means that portion of a building between any floor and the next floor above, except that the topmost story shall be that portion of a building between the topmost floor and the ceiling or roof above it. If the finished floor level directly above a basement, cellar or unused floor space is more than six feet above the grade for more than 50 percent of the total perimeter of the building or is more than 12 feet above the grade at any one point, then such basement, cellar or unused floor space shall be considered a story. A story as used here shall not exceed 15 feet in height. (Ord. 573 § 2, 1990).