Minimum size. Every one-story dwelling hereafter erected or placed in an R-1 Residence District shall have a minimum living floor space, as herein defined, of not less than 1,600 square feet. In a one-and-one-half-story dwelling, there shall be a finished minimum living floor space of 1,200 square feet on the first floor and a minimum of 600 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 story is constructed and the second floor plan for the structure is filed with the Building Inspector 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 1,100 square feet on the first floor and a minimum living floor space of 800 square feet on the second floor.