ADU Financing 101

Most California homeowners have two things working in their favor when it comes to financing an ADU: significant home equity, and a rental market that makes the project cash-flow positive relatively quickly.

The challenge is that ADU financing doesn't work exactly like a standard mortgage, and some products are significantly better than others for this use case.

Start With Your Equity

Every financing option for an ADU runs through home equity. If you don't have meaningful equity in your home, most lenders won't finance the project at all.

A rough rule: lenders will let you borrow up to 80–85% of your home's current value, minus what you still owe on your mortgage. That's your available equity.

Example: Home worth $900,000, mortgage balance $400,000. Available equity: ($900,000 x 0.80) - $400,000 = $320,000.

If your ADU costs $220,000, you have enough equity to cover it. If your ADU costs $350,000, you're at the limit and would need strong credit and income to qualify.

Cash-Out Refinance

You replace your existing mortgage with a new, larger mortgage and pocket the difference. The ADU construction cost comes out of that cash.

Works best when: Current mortgage rates are close to or lower than your existing rate. If you locked in at 3% and current rates are 7%, this option costs you dearly on your primary mortgage.

Rate: Fixed, same as a standard 30-year mortgage Pros: Simple, one payment, long amortization Cons: You refinance your entire mortgage balance, which is painful if rates have risen

Right now, for most homeowners who locked in low rates in 2020–2022, a cash-out refinance makes little financial sense. You'd be giving up a low rate on your existing balance.

Home Equity Line of Credit (HELOC)

A HELOC is a revolving line of credit secured by your home equity. You draw what you need, when you need it, and pay interest only on what you've drawn.

Works best when: You want flexibility and are not paying off the primary mortgage. Ideal if you have a low-rate first mortgage you want to keep.

Rate: Variable, tied to the prime rate. Typically prime + 0–2%. Pros: Flexible draws match construction payment schedule, interest-only during draw period, keep your existing mortgage intact Cons: Variable rate adds uncertainty, HELOC can be frozen if your home value drops

For most homeowners right now, a HELOC is the most practical path to ADU financing. You keep your existing mortgage untouched and tap only what you need.

Home Equity Loan

A home equity loan is a second mortgage: you borrow a fixed lump sum at a fixed rate, keep your primary mortgage, and make two separate payments.

Rate: Fixed, typically 0.5–1% higher than primary mortgage rates Pros: Predictable payment, keeps existing mortgage Cons: Lump sum disbursed upfront (you pay interest on money you haven't used yet during construction), two monthly payments

If you prefer a fixed rate over a HELOC's variable rate, and you can estimate your total construction cost accurately, a home equity loan is a reasonable option.

Construction-to-Permanent Loan

A construction loan funds the project while it's being built, with draws released to the contractor at key milestones. Once construction is complete, it converts to a permanent mortgage.

Works best when: You need a single loan to cover everything, including your current mortgage, and don't have enough equity for a HELOC to cover the full project cost.

Rate: Variable during construction, then fixed at conversion Pros: Purpose-built for this use case, structured disbursements protect you Cons: More paperwork, higher rates than a standard mortgage, lender typically requires an inspection before each draw

ADU-Specific Lenders

A handful of lenders have developed products specifically for ADU projects. RenoFi and some local credit unions offer renovation loans that underwrite based on your home's projected value after the ADU is complete (rather than current value), which unlocks more borrowing capacity for homeowners with less existing equity.

These products are worth exploring if your current equity is tight but the completed ADU would significantly increase your home's value.

California Grant and Loan Programs

The California Housing Finance Agency (CalHFA) offers ADU-related assistance for qualifying homeowners:

• ›ADU Grant Program: Provides up to $40,000 toward predevelopment costs (design, permits, site prep) for owner-occupied homes. Income limits apply. Funding has been limited and competitive.
• ›CalHFA ADU Loan: A deferred-payment junior loan for qualifying first-generation homebuyers.

Local programs also exist. Some cities, particularly in the Bay Area, offer low-interest or forgivable loans for ADUs that will be rented at below-market rates.

Check your city's planning or housing department website for local programs. They tend to be underused because they're not well-advertised.

What to Tell Your Lender

When you approach a lender about ADU financing, come prepared with:

• ›Your home's current estimated value (a recent appraisal or tax assessment)
• ›Your current mortgage balance and rate
• ›A realistic ADU construction budget
• ›Your household income and credit score
• ›If possible, projected rental income from the ADU

Lenders who are experienced with ADUs will ask about the rental income. Some conventional lenders will count projected rental income toward qualifying income, which improves your debt-to-income ratio.

The Practical Path

For most California homeowners with a low-rate first mortgage and at least $150,000 in usable equity, the practical path is a HELOC for its flexibility, low initial costs, and ability to leave the primary mortgage untouched. If rates feel uncomfortable, layering in a home equity loan for the majority of the cost with a small HELOC as a contingency buffer is a reasonable hedge.

Get quotes from at least two or three lenders. HELOC rates and terms vary more than you'd expect.