Three-Family Residential Subdistricts, as indicated by the designation 3F on said Maps. The Three-Family Residential Subdistricts are established to preserve the 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 and to allow minor changes to occur as-of-right. In a 3F Residential Subdistrict, the maximum number of Dwelling Units allowed in a single Building, including a Town House Building or Row House Building, shall be 3.