I’m Michael DiVita — DRE #01372066 | NMLS #241655, DiVita Home Finance (DRE #01818285 | NMLS #323700), Tiburon, CA. I’ve been in California mortgage lending since 2000 and founded DiVita Home Finance in 2007. ADU financing is one of the most active areas I work in — I help California homeowners find the right structure so they don’t leave money on the table or disrupt a low existing rate unnecessarily. Call (800) 239-1103.
California passed sweeping ADU-friendly legislation that has made accessory dwelling units the state’s fastest-growing housing type. Whether you’re building a backyard cottage, converting a garage, or adding an in-law suite, financing the ADU correctly can mean the difference between a profitable investment and a financial stretch. The financing decision starts with one question: what is the rate on your existing first mortgage?
Your ADU Financing Options
A HELOC is the most popular choice for California homeowners who bought or refinanced between 2020 and 2022 at 2.5%–3.5%. You draw funds as needed during construction, paying interest only on what you’ve used. Your existing low-rate first mortgage stays completely untouched. This keeps your total housing cost lower than any option that involves refinancing the primary loan. The variable rate on the HELOC is the tradeoff, but the blended cost of a low fixed first plus a variable HELOC is almost always better than refinancing everything into one new first at today’s rates.
A home equity loan (HELOAN) is a fixed-rate second mortgage that provides a single disbursement for your ADU budget. If you want a fixed rate and predictable payment on the construction financing without touching the first mortgage, this is the right structure. You trade the HELOC’s draw flexibility for rate certainty.
A cash-out refinance makes sense when your existing rate is already at or near current market rates, making the cost of touching the first mortgage acceptable, or when you need a large amount ($300,000+) that would exceed HELOC availability. It’s one loan, one payment, fixed rate. For rate-protected borrowers, this is usually the wrong choice — but I model both and show you the 5-year cost difference before you decide.
After-renovation value (ARV) lending is available through some lenders who will lend against the projected post-ADU appraised value rather than current equity. This is powerful for properties where current equity is modest but the completed ADU will significantly increase value. Not all lenders offer this — I have access to programs that do.
California ADU Cost and Rental Income Estimates (2026)
| ADU Type | Typical Cost Range | Typical Rent (Bay Area) | Annual Rental Income |
|---|---|---|---|
| Garage conversion | $80,000–$150,000 | $1,800–$2,800/mo | $21,600–$33,600 |
| Attached addition | $150,000–$250,000 | $2,200–$3,500/mo | $26,400–$42,000 |
| Detached cottage | $200,000–$400,000 | $2,800–$4,500/mo | $33,600–$54,000 |
Using ADU Rental Income to Qualify for a Larger Mortgage
If you’re buying a property with an existing permitted ADU, rental income from the unit can be used to qualify for a larger mortgage. Lenders typically allow 75% of documented market rent as qualifying income. On a property where the ADU rents for $2,800/month, that adds $2,100/month in qualifying income — at a 43% DTI, that’s enough to support approximately $315,000 in additional loan amount. This is one of the most underused qualification strategies I see California buyers miss.
Frequently Asked Questions — ADU Financing California
What is the best way to finance an ADU in California without refinancing my existing mortgage?
A HELOC or fixed-rate second mortgage (HELOAN) are the best options for preserving your existing first mortgage rate. Both use your home equity as collateral without touching the primary loan. A HELOC gives you a revolving credit line to draw from as construction progresses — ideal for phased builds. A HELOAN provides a fixed lump sum at a fixed rate for borrowers who want payment certainty. Either way, your original low-rate first mortgage stays exactly as it is. I compare both structures for every ADU client before recommending one.
How much can I borrow for an ADU in California through a HELOC?
Most HELOC programs allow a combined LTV (first mortgage plus HELOC) of 80–85%. On a $1,500,000 California home with a $400,000 existing mortgage, 80% CLTV allows total liens of $1,200,000 — giving you up to $800,000 in HELOC capacity. Most ADU builds cost $80,000–$400,000, well within reach for homeowners who purchased in the last 5–10 years in California’s appreciating markets. For homes valued over $2M, I have access to jumbo HELOC programs with higher CLTV limits than standard bank products offer.
Can I refinance into a permanent loan using ADU rental income after the unit is built?
Yes — once the ADU is completed, permitted, and rented with a signed lease, you can refinance the HELOC or construction financing into a permanent first mortgage using the ADU rental income to qualify. Fannie Mae allows up to 75% of documented ADU rent to offset the mortgage payment in DTI calculations. The post-ADU appraised value (higher than before construction) also improves your LTV — often producing better loan terms on the permanent financing than you’d have qualified for during the build. This makes the HELOC-to-permanent refinance a strong exit strategy for many California ADU projects.
See all ADU financing options at DiVita Home Finance
Talk to Michael Directly
DiVita Home Finance | Tiburon, CA | In lending since 2000, founded DiVita Home Finance in 2007. Michael DiVita DRE #01372066 | NMLS #241655. Company DRE #01818285 | NMLS #323700.
💬 Text: (310) 849-9124
