A building which is partially or wholly destroyed by fire, act of God or other casualty beyond the control of the owner may be reconstructed within one year thereafter; provided, however, that this period for reconstruction may be extended by the Zoning Hearing Board upon suitable application within that year, for such additional time as said Board shall determine, upon a showing to said Board that strict compliance with this one-year period will work unwarranted hardship or injustice to the owner, and that such reconstruction thereafter will not be contrary to the public interest. Said reconstruction shall conform to all provisions of this chapter.