The even numbers shall be put upon the east and north sides of the streets, and the odd numbers upon the south and west sides, allowing approximately 20 feet for each number. In all basements occupied as business rooms, the half number shall be used. Stairways leading to the upper stories of buildings shall have the same number as the room on the street closest to the stairway, and the letter "A" to designate second story, the letter "B" to designate third story, and so on, affixed to such numbers. In case a stairway is located on the side of a street, the stairway shall have the same number as the room to which it is attached. On all stairways located on or near the dividing line, the stairways shall bear the same number as the room having the lowest number. (1979 Code 93.12)