The notices required in Section 54 shall be given in the following manner: The enforcement agency shall post conspicuously at least one copy of the notice on the building alleged to have become substandard, and shall send another copy by registered or certified mail, postage prepaid, return receipt requested, to the person owning the land on which the building is located, as that person's name and address appear on the last equalized assessment roll, or as known to the clerk of the governing board of the enforcement agency and to any mortgagee or beneficiary. If the address is unknown to the enforcement agency, this fact shall be stated in the copy so mailed and it shall be addressed to this person at the county seat of the county where the property is situated.

The officer or employee of the enforcement agency upon giving the notice, shall file an affidavit with the clerk of the governing board of the enforcement agency, certifying the time and the manner in which the notice was given along with any receipt card returned in acknowledgment of the receipt of the notice by registered mail. The failure of any owner or other person to receive the notice, shall not affect in any manner the validity of any proceedings taken hereunder.