"Accessory building or structure" shall mean a structure and/or use which is subordinate, secondary, incidental to and customary in connection with the principal building or use and located on the same lot as the principal building or use. Residential accessory structures include detached garages, tool and garden sheds, tennis courts, swimming pools and similar facilities. Such accessory structures are subject to the following additional requirements:
(a) In the RE, R-1, R-2, and R-3 Districts, no separate accessory structure can be erected on a vacant lot, or any lot where there is no principal residential structure, without the approval of the Board of Zoning Appeals. Such approval, if granted, shall specify the conditions under which such accessory building can be erected.
(b) An accessory use or structure shall not exceed eighteen (18) feet in height.
(c) An unattached accessory structure shall be located within any side or rear yard. Such accessory structure shall be constructed not closer to the side lot line than the side yard requirement of the district where it is located, and not less than five (5) feet from the rear lot line, unless such lot backs unto a dedicated right-of-way or alley, in which case such setback shall not be less than ten (10) feet from such right-of-way or alley.
(d) The use of all accessory structures shall conform to the definition above, and no accessory structure shall be used for human habitation, or for commercial purposes.