Lot area. Every building erected or structurally altered after January 4, 1955, shall provide a lot area of not less than 7,200 square feet per family. In the R-2 Residential District a two-family dwelling may be permitted as a conditional use on a lot that was of record as of January 4, 1955, and that has an area less than 14,400 square feet. However, such lot must have a minimum size of 7,200 square feet and must meet the setback and yard requirements for the R-2 District.