Notwithstanding any other provision of this section, the Secretary is authorized to insure any mortgage which involves a principal obligation not in excess of the applicable maximum dollar limit under subsection (b) of this section and not in excess of 100 per centum of the appraised value of a property upon which there is located a dwelling designed principally for a single-family residence, where the mortgagor establishes (to the satisfaction of the Secretary) that his home which he occupied as an owner or as a tenant was destroyed or damaged to such an extent that reconstruction is required as a result of a flood, fire, hurricane, earthquake, storm, or other catastrophe which the President, pursuant to sections
5122
(2) and
5170 of title
42, has determined to be a major disaster.