(a) The fair value of property shall be determined by appraisal by a competent appraiser at the time of the making or acquiring of a mortgage loan or investing in a contract for the deed thereon, except, that as to bonds or notes secured by mortgage or trust deed guaranteed or insured by the Federal Housing Administration, or guaranteed or insured as to principal in full or in part by the Administrator of Veterans' Affairs, or guaranteed or insured by the Farmers Home Administration, the valuation made by such administration or administrator shall be deemed to have been made by a competent appraiser for the purposes of this subsection.
(b) Buildings and other improvements located on the mortgaged premises shall be kept insured for the benefit of the mortgagee against loss or damage from fire in an amount not less than the unpaid balance of the obligation, or the insurable value of the property, whichever is the lesser.
(c) An insurer shall not make or acquire a loan or loans upon the security of any one parcel of real property in aggregate amount in excess of $25,000 or more than the amount permissible under section 553 of this title, whichever is the greater.