ADU Financing 2026: How to Finance an Accessory Dwelling Unit Purchase or Construction

An accessory dwelling unit is a secondary residential unit on a single-family lot, either attached, detached, or converted from existing space such as a garage or basement. In 2026, ADUs are appraised and financed routinely across most markets. Knowing the available financing paths matters for buyers purchasing properties with existing ADUs and for homeowners adding one.

Purchase Loans That Include ADU Value

Fannie Mae and Freddie Mac both allow ADU value to be included in the appraised value on a standard purchase or refinance. The appraiser must identify comparable sales that include ADUs to support the value. If no ADU comps exist, the lender may limit or exclude the ADU value from the appraised total. An ADU on a single-family property is still classified as a 1-unit property for LTV and program purposes.

Construction Financing Options

• ✦HELOC: existing homeowners can draw against current equity to fund construction, most common path
• ✦Cash-out refinance: refinance existing first mortgage to fund ADU construction, rate environment matters in 2026
• ✦RenoFi loans: renovation-specific product that lends against after-renovation value, not current value
• ✦Construction-to-permanent: one-time close with ADU build as the improvement, applies if building from lot
• ✦FHA 203(k): applies only if the property is being purchased and the ADU is part of a rehabilitation plan

Permit Requirements and Financing

Lenders require the ADU to be legally permitted. Unpermitted ADUs create appraisal and lending complications. Fannie Mae will not include unpermitted ADU value in the appraisal. Some portfolio lenders will lend with unpermitted ADUs but adjust LTV or value accordingly. Before advising a client on ADU financing, confirm the unit is permitted or that the build plan includes permitting.