Maximum number of dwelling units. The maximum number of dwelling units permitted within an individual PRD District, or in the combination of two or more contiguous PRD Districts, that are served by the Hamlet Sewer District and the Woodstock Water District, shall be 80 dwelling units. In areas not served by municipal water and sewer, the maximum number of units permitted shall be 20 units. In the case of senior citizens' housing, the maximum number of units in a structure shall be 12 for one-story construction and 24 for two-story construction. In the case of family housing, or a mix of units in a single structure, the maximum number of units in a single structure shall be four and eight units, respectively.