The yard areas required by this title for a particular building shall not be diminished and shall not be included as a part of the required lot or yard areas of any other building, excepting the Planning and Zoning Commission shall have the power to alter the required setback line in restricted districts in the case of public or semipublic buildings, after a public hearing, and after showing that such action will not cause damage, and will be in accord with the general purpose of this title. The yard areas of buildings existing at the time of the adopting of this title shall not be diminished below the requirements herein provided for buildings hereafter erected, excepting as provided herein, and such required areas of any building hereafter erected. (Ord. 19, 12-5-1973)