Number of buildings per lot. In the RH, CR-10, ER-1 and SR-4 Districts, only one principal building shall be permitted on any one lot. In the TR-6, MR-8, MR-10, NO, PO, NB, PB, GB, CB, PI, GI and HI Districts, more than one principal building shall be permitted on any one lot upon the granting of a conditional use permit for a group development in compliance with Article VI.