Before establishing or altering any building or veranda line, and before making any appraisal of damages or assessment of benefits therefor, a public hearing shall be given by the Commission to all parties in interest, and notice of the time and place of such hearing shall be given by causing a copy of the proposed order designating and establishing or altering any building or veranda line, with a notice of the time and place of hearing thereon, to be filed in the Town Clerk's office and published in the same manner as provided for giving notice of a public hearing in § 3-8 of this Charter, and by depositing a like copy in any post office in said Town, postage prepaid, directed to the person or persons interested at their last-known post office address.