Mortgage and appraisal policies determine how a participating lender may classify a property, document an accessory unit, or consider rental income. They do not decide whether local authorities allow the unit or whether it complies with building, fire, utility, or occupancy requirements. A policy that mentions ADUs is not an offer of a loan or an individual approval.
Check the policy issuer and current guide
Identify the loan program, property configuration, transaction type, and policy date. Then check the current official handbook or selling guide, since older letters and copied summaries may have been superseded. HUD identifies Handbook 4000.1 as the consolidated source for FHA Single Family policy; its page records an August 12, 2026 update. The 2023 HUD ADU mortgagee letter remains historical context, but current ADU treatment should be checked in the handbook and with the participating lender.
Rental income and appraisal documentation
Fannie Mae and Freddie Mac publish conventional underwriting rules for specified transactions involving ADUs. Their guides describe how rental income may be documented and limited, when appraisals or rental analyses are needed, and what property or borrower conditions apply. The details differ by transaction and guide version. Fannie Mae’s March 2026 appraiser update also describes expanded ADU eligibility under UAD 3.6, including selected multi-ADU and manufactured-housing cases; this is an appraisal and financing-policy update, not a zoning change.
For an FHA, Fannie Mae, or Freddie Mac loan, check the current handbook or guide section and ask the lender which documentation, legal-status, appraisal, reserve, and income rules it will apply. Lenders may require additional documentation or impose overlays. Do not carry a number from an older policy letter into a current loan decision without checking the current source.
Canadian secondary-suite refinancing is a separate path
CMHC Refinance is a Canadian mortgage-insurance product described for financing construction and completion of a secondary suite in an existing home. The published criteria include ownership and occupancy conditions, local bylaw compliance, project documentation, and limits on use of funds. The product page states that additional lender conditions may apply. It does not decide whether a specific suite is legal, whether a borrower meets underwriting requirements, or whether a lender will offer the financing.
This product is distinct from Canada’s proposed Secondary Suite Loan Program, which Budget 2025 said would not be implemented. Do not treat one as a replacement for the other without a current official announcement.
Keep the questions separate
For a reliable project picture, check three decisions independently: whether the unit is permitted and compliant locally; whether it can be appraised and documented under the relevant loan policy; and whether the borrower qualifies with the chosen lender. Mortgage eligibility cannot substitute for a zoning, permit, inspection, occupancy, or utility determination. This guide is informational and does not provide individual financial advice.