If the owner of a building fails to comply with a notice served on or delivered to him in accordance with
subsection (3) in respect of such building, the local authority in question may demolish such building, remove the material of which such building consisted and any other material or rubbish from the site in question and otherwise clean up such site, and may recover the costs thereof from such owner: Provided that such local authority may sell such material and may utilize the proceeds of such sale to defray the costs of such demolition,
removal or clean-up and shall pay the balance, if any, of such proceeds to such owner.