The minimum ground-floor living area, exclusive of steps, porches, bays, utility rooms (heating or laundry) or attached sheds, shall be as follows:
A. Seven hundred fifty square feet for every dwelling one story high.
B. Six hundred square feet for every dwelling 1 1/2, two or 2 1/2 stories in height.
C. Six hundred square feet for every dwelling 1 1/2, two or 2 1/2 stories high where a one-car garage, 200 square feet in area, having a 50% or more habitable floor area over the same is erected as a structural part of the building.