Notwithstanding the otherwise applicable provisions of subsection 10-5-6B1 of this title, for any principal structure on bluff/ravine property that has a walkout basement with a rear wall located in a ravine or within a ravine protection area, a percentage of the floor area of the walkout basement shall be included in the gross floor area of the bluff/ravine property. The total additional square footage to be included in the gross floor area calculation for any such walkout basement shall be forty percent (40%) of the total area, in square feet, of all portions of the finished floor that are enclosed by lines extending perpendicular from the basement wall facing the ravine to the opposite basement wall across the full width of the exposed portion of the basement wall at a height of two feet (2') above grade. The resulting square footage shall be included in the gross floor area of the bluff/ravine property. See section 10-13-1 of this title, illustration 17. (Ord. 99-9, 3-8-1999)