Management and Sales Types and Investor Sponsored Projects. (1) If the date of the first principal payment is one year, or less than one year following the date of such initial insurance endorsement, the mortgagee, upon such first principal payment date, shall pay a second premium equal to one-half of one percent of the average outstanding principal obligation of the mortgage for the following year which shall be adjusted so as to accord with such date and so that the aggregate of the first and second premiums shall equal the sum of

One percent per annum of the average outstanding principal obligation of the mortgage for the period from the date of initial insurance endorsement to the date of first principal payment, and

One-half of one percent of the average outstanding principal obligation of the mortgage for the year following the date of the first principal payment.

If the date of the first principal payment of a mortgage is one year or less than one year following the date of the initial insurance endorsement and the mortgage is paid in full prior to the date of such first principal payment, the first and only premium collected shall be adjusted so that the total premium shall equal one percent per annum of the average outstanding principal obligation of the mortgage for the period from the date of initial insurance endorsement to the date the mortgage was paid in full.

Purchasing cooperatives. The provisions of paragraph (a) of this section do not apply to the mortgage of a purchasing nonprofit cooperative housing corporation or trust where such mortgage is endorsed for insurance pursuant to the sale of an Investor Sponsored Project to such purchasing nonprofit cooperative housing corporation or trust.

Existing Construction. The provisions of paragraph (a) of this section shall apply to a mortgage covering Existing Construction which involves insurance of advances for Commissioner approved or required repairs, improvements, alterations and additions.

Supplementary loan; insurance of advances. The provisions of paragraph shall apply to a supplementary loan involving insurance of advances.