Except as may be specifically authorized hereunder, no land shall be used and no building, structure or sign shall be erected, modified, enlarged or used unless such action conforms to all of the applicable provisions of this chapter. Every building, structure or sign hereafter erected and every use hereafter initiated shall be located on a lot as defined by this chapter, and in no event shall there be more than one main or principal residential building, together with its accessory buildings, on one lot. In the case of dormitories erected for institutional use, planned developments approved pursuant to this chapter, and multifamily dwellings approved pursuant to this chapter, the requirements of one principal residential building per lot is waived.