If, at or prior to final confirmation of any special assessment, more than fifty percent of the number of owners of privately owned real property to be assessed for any improvement, or in case of paving or similar improvements, more than fifty percent of the number of owners of frontage to be assessed for any such improvement, shall object in writing to the proposed improvement it shall not be made by the proceedings authorized in this Charter without a five-sixths vote of the members of the Council, provided that this section shall not apply to sidewalk construction.