The preceding Sections 7-2-10, 7-2-11, 7-2-12 and 7-2-13 shall not apply to any owner or agent of real property or any contractor or builder or other person who first obtains a written permit therefor issued by the City Council; provided, however, that except in case of necessity, no such permittee shall encumber or obstruct more than one-third (1/3) of any street, alley or sidewalk; provided, that no such obstruction continues in any case longer than may be necessary in the diligent and prompt execution of the work. (1994 Code)