The minimum first-floor area of a one-family, story-and-a-half dwelling shall be 800 square feet, provided that the second-story area is finished; if it is not finished, the minimum first-floor area shall be 925 square feet. The minimum first-floor area of a two-family, story-and-a-half dwelling shall be 1,600 square feet, provided that the second-story area is finished; if it is not finished, the minimum first-floor area shall be 1,850 square feet.