No junked motor vehicle or part thereof, or motor vehicles incapable of normal operation upon the highway, shall be permitted on the premises of any service station. It shall be deemed prima facie evidence of violation of this Chapter if more than three motor vehicles incapable of operation are located at any one time upon any premises not within a closed and roofed building excepting, however, that a number not exceeding six motor vehicles may be located upon any service station premises outside of a closed or roofed building for a period of time not to exceed 30 days and providing that the owners of the motor vehicles are awaiting their repair or disposition. All such vehicles shall be stored in one area, which shall be buffered in accordance with subsection 26-35.1 (Buffers).