How Do You Finance an ADU (Accessory Dwelling Unit)?
An Accessory Dwelling Unit (ADU) — backyard cottage, garage conversion, or basement suite — can be financed several ways: a cash-out refinance using your home's existing equity (most common), a renovation loan (FHA 203k or HomeStyle) that rolls ADU construction costs into your mortgage, a HELOC or home equity loan, or a construction loan for ground-up builds. A key financing advantage: Fannie Mae allows lenders to count up to 75% of projected ADU rental income toward qualifying income, significantly expanding borrowing power. ADU construction costs in Oregon and California typically range from $150,000-$350,000 for a detached unit.
Key Facts
Cash-Out Refinance: The Most Common ADU Financing Path
If you have sufficient equity in your home, a cash-out refinance replaces your current mortgage with a new, larger one — and the difference funds your ADU construction. Example: your home is worth $600,000 with a $350,000 mortgage balance. A 75% LTV cash-out refinance produces a new $450,000 mortgage, giving you $100,000 in cash (minus closing costs) to fund the ADU. If construction costs exceed the available equity, you may need to supplement with savings, a HELOC, or a construction loan. The advantage: a single mortgage at a fixed rate with no second lien.
Renovation Loans: Roll ADU Costs Into Your Mortgage
FHA 203(k) and Fannie Mae HomeStyle renovation loans allow you to borrow the cost of construction improvements — including ADU construction — as part of your mortgage. The loan is based on the as-completed appraised value of the property (including the ADU), and funds are released in draws as construction progresses. This is particularly useful when your current equity isn't sufficient for a cash-out refinance. HomeStyle loans allow up to 75% of the as-completed appraised value. FHA 203(k) allows financing with as little as 3.5% down on a purchase or the full renovation cost on a refinance.
Using Projected ADU Rental Income to Qualify
Fannie Mae's accessory dwelling unit income policy allows lenders to count up to 75% of the projected monthly ADU rental income toward the borrower's qualifying income. This is a significant advantage: if your ADU is projected to rent for $1,800/month, $1,350/month can be added to your qualifying income — potentially allowing you to qualify for $200,000+ more in loan amount than you could without the ADU income. The rental projection must be supported by a qualified appraisal or rent analysis. This policy applies to both purchase and refinance transactions.
Oregon and California ADU Regulations
Both Oregon and California have enacted statewide legislation making ADU construction easier. Oregon's HB 2001 requires all cities with populations over 25,000 to allow ADUs in all residential zones. California's SB 9 and AB 68 streamlined ADU permitting statewide, reduced fees, eliminated owner-occupancy requirements for many ADU types, and allow up to two ADUs on a single-family lot. These regulatory changes have made ADU construction financially viable for thousands of homeowners — and the combination of state permitting reform with Fannie Mae's rental income qualification creates a compelling financial case for ADU investment.
Licensed in Oregon & California · NMLS #1498678