(1) Residential districts shall be designated as: "R-1" Residential, "R-1A" Residential, "R-2" Residential, "R-3" Residential, "R-4" Residential, "R-5" Residential, "R-5A" Residential, "R-6" Residential, "R-7" Residential, "R-8" Residential, "R-9" Residential, "R-9A" Residential, "R-10" Residential, "R-10A" Residential, "R-10B" Residential, "R-11" Residential, "R-11A" Residential, "R-12" Residential, "R-13" Residential, "R-14" Residential, "R-15" Residential, "R-16" Residential, "R-18" Residential, "R-19" Residential, "R-20"Residential, "RC-1" Residential, "RC-2" Residential, "RC-3" Residential, "RC-4" Residential, and "RC-6" Residential.