This bill amends the National Housing Act to establish a new program within two years, directing the Secretary of Housing and Urban Development to insure certain second liens . These liens are specifically for the purpose of financing the construction of accessory dwelling units (ADUs) , which are defined as modular, manufactured, or converted units with kitchen, sleeping, and bathroom facilities, added to or detached from a single-family dwelling. The program sets a maximum loan amount for insured second liens, generally limited to the lesser of 30 percent of the FHA single-unit loan limit or 100 percent of the projected property value after ADU construction, when combined with other liens. The Secretary may increase this amount based on 50 percent of projected rental income from the ADU, and will charge an annual premium not exceeding 1 percent of the principal insured amount. Borrowers must apply and certify property ownership, and the Secretary must report annually to Congress on program activities. Furthermore, the Director of the Federal Housing Finance Agency (FHFA) is mandated to permit Fannie Mae and Freddie Mac to purchase and securitize these insured ADU construction loans. However, the Director retains the authority to prohibit such activities if market pressures present an excessive and unmitigable risk, provided Congress is notified in writing. The FHFA Director must also include relevant information about these loans in their annual report.