12 USC 371 - Real estate loans

(a) Authorization to make real estate loans; orders, rules, and regulations of Comptroller of the Currency 
Any national banking association may make, arrange, purchase or sell loans or extensions of credit secured by liens on interests in real estate, subject to section 1828 (o) of this title and such restrictions and requirements as the Comptroller of the Currency may prescribe by regulation or order.
(b) Eligibility for discount as commercial paper of notes representing loans financing construction of residential or farm buildings; prerequisites 
Notes representing loans made under this section to finance the construction of residential or farm buildings and having maturities not to exceed nine months shall be eligible for discount as commercial paper within the terms of the first paragraph of section 343 of this title if accompanied by a valid and binding agreement to advance the full amount of the loan upon the completion of the building entered into by an individual, partnership, association, or corporation acceptable to the discounting bank.