The mortgage shall have a maturity satisfactory to the Commissioner, and shall contain complete amortization or sinking-fund provisions satisfactory to the Commissioner.

(a) The maximum mortgage term may not exceed the lesser of:

(1) Any limits included under the applicable section of the Act.

(2) Thirty-five years for existing projects, except that the mortgage term may be up to 40 years under terms and conditions established by the Commissioner, and 40 years for proposed construction and substantial rehabilitation projects.

(3) Seventy-five percent of the estimated remaining economic life of the physical improvements.

(b) The minimum mortgage term shall not be less than 10 years.