(4)   Multiple Principal Uses and Buildings.
(a)   No more than one principal use is allowed per lot in RSD, RSA, and RTA zoning districts, except as otherwise expressly stated in this Zoning Code. Multiple principal uses are allowed on a single lot in RM and RMX districts.
(b)   No more than one principal building is allowed per lot in RSD, RSA, and RTA zoning districts. Multiple principal buildings may be placed on a single lot in RM and RMX districts. Dormitories and recreation-related buildings accessory to education facilities and residential dwelling units accessory to religious assembly uses are exempt from limitations on the number of buildings per lot.