To amend the National Housing Act to direct the Secretary of Housing and Urban Development to establish a program to insure certain second liens secured against property for the purpose of financing the construction of an accessory dwelling unit, and for other purposes.

This bill establishes a program to insure second mortgages (loans taken out after the primary mortgage) for financing accessory dwelling units (ADUs) on single-family properties. The Secretary of Housing and Urban Development must create the program within two years, setting loan limits (up to 30% of a standard mortgage amount or 100% of the property's after-construction value, with potential increases based on 50% of projected rental income) and requiring borrowers to own the property and apply for insurance. It also allows Fannie Mae and Freddie Mac to purchase and securitize these insured loans, unless the Federal Housing Finance Agency determines market risks require a prohibition. The program requires the Secretary to submit annual reports to Congress on its implementation starting one year after enactment.