Minimum size. Every one-story dwelling hereafter erected or placed in an R-2 Residence District shall have a minimum living floor space, as herein defined, of not less than fourteen hundred (1,400) square feet. In a one-and-one-half (1 1/2) story dwelling, there shall be a finished minimum living floor space of eleven hundred (1,100) square feet on the first floor and a minimum of 550 square feet on the second floor. The second floor area may be left unfinished; provided, however, that rough facilities shall be extended to the second floor and that a permanent stairway to the second floor is constructed and that a practical, second floor plan for the structure is filed with the Construction Official at the time of the making of the application for the building permit. In a two story dwelling, there shall be a minimum living floor space of 1,000 square feet on the first floor and a minimum living floor space of 800 square feet on the second floor.