Two-Family Residential Subdistricts, as indicated by the designation 2F on said Maps. The Two-Family Residential Subdistricts are established to preserve, maintain, and promote low density two-family neighborhoods, to preserve existing structures, to provide for new infill construction appropriate to the existing fabric, and to allow minor changes to occur as-of-right. In a 2F Residential Subdistrict, the maximum number of Dwelling Units allowed in a single Building shall be 2.