In R residence districts, conversions of existing residential buildings shall be governed by the following:
A. The quotient secured by dividing the floor area of all dwelling units on a lot by the number of dwelling units on such lot shall not be less than five hundred (500) square feet.
B. No existing residential use shall be so converted as to conflict with, or further conflict with, the requirements in subsection A of this section.
C. Where applicable, an efficiency dwelling unit or lodging room may be considered 0.75 dwelling unit in determining compliance with subsection A of this section. (1990 Code §21.3.030)