A city shall establish a self-supported municipal improvement district debt service fund whenever any self-supported municipal improvement district bonds are issued and outstanding, other than revenue bonds, and shall certify taxes to be levied against all of the property in the district for the debt service fund in the amount necessary to pay interest as it becomes due and the amount necessary to pay, or to create a sinking fund to pay, the principal at maturity of all self-supported municipal improvement district bonds as authorized in section 386.11, issued by the city. However, parcels of property which are assessed as residential property for property tax purposes at the time of the issuance of the bonds are exempt from the tax levied under this section until the parcels are no longer assessed as residential property or until the residential properties are designated as a part of a historic district or property classified as residential property under section 441.21, subsection 14, paragraph “a”, subparagraph (6).