Three-Family Residential Subdistricts, as indicated by the designation 3F on said Maps. The Three-Family Residential Subdistricts are established to encourage low-density three-family areas with a variety of housing types appropriate to the existing fabric including one-, two-, but no more than three-family Dwellings. In a 3F subdistrict the maximum number of Dwelling Units allowed in a single Building, in a Town House Building, or in a Row House Building shall be 3, and the maximum number of Town House Buildings or Row House Buildings attached in a row shall be 3; a greater number of units up to 4 in a Building and a greater number of Buildings up to 4 attached in a row shall be conditional.