No required yard or other open space around an existing building, or which is hereafter provided around any building for the purpose of complying with the provisions of this title, shall be considered as providing a yard or open space for any other building; nor shall any yard or other required open space on an adjoining lot be considered as providing a yard or open space on a lot whereon a building is to be erected or established. This section shall be so construed to mean only one main building may be permitted on one lot unless otherwise hereinafter provided. (Ord., 6-8-1989)