(a) Prepayment privilege. Except as provided in paragraph (c) of this section or otherwise established by the Commissioner, the mortgage shall contain a provision permitting the mortgagor to prepay the mortgage in whole or in part upon any interest payment date, after giving the mortgagee 30 days' notice in writing in advance of its intention to so prepay.

(b) Prepayment charge. The mortgage may contain a provision for such charge, in the event of prepayment of principal, as may be agreed upon between the mortgagor and the mortgagee, subject to the following:

(1) The mortgagor shall be permitted to prepay up to 15 percent of the original principal amount of the mortgage in any one calendar year without any such charge.

(2) Any reduction in the original principal amount of the mortgage resulting from the certification of cost which the Commissioner may require shall not be construed as a prepayment of the mortgage.

(c) Prepayment of bond-financed or GNMA securitized mortgages. Where the mortgage is given to secure GNMA mortgage-backed securities or a loan made by a lender that has obtained the funds for the loan by the issuance and sale of bonds or bond anticipation notes, or both, the mortgage may contain a prepayment restriction and prepayment penalty charge acceptable to the Commissioner as to term, amount, and conditions.

(d) HUD override of prepayment restrictions. In the event of a default, the Commissioner may override any lockout, prepayment penalty or combination thereof in order to facilitate a partial or full refinancing of the mortgaged property and avoid a claim.