For a single-family dwelling, the minimum land area shall be 11,000 square feet and the minimum width of the lot at the front building line shall be not less than 85 feet. However, this shall not apply to prevent the construction of a single-family dwelling on a lot, existing on the date of this enactment and not adjoined at the side by another unoccupied lot or other unoccupied land in the same ownership, having an area of not less than 7,500 square feet and a width at the front building line of not less than 65 feet.