That portion of a building included between the surface of any floor above the finished exterior grade at the front of the building, and the surface of the floor next above it, or if there be no floor above it, then the space between any floor and the ceiling next above it. A lower story is a basement when the average elevation of the proposed finished exterior grade at the front of the building is above the middle of the interior height of such story. The first story is the lower story and may occur on staggered levels. [Ord. 1267, 09-14-09.]