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 common conversations I have with California homeowners right now — the right structure saves tens of thousands over the life of the project. Call (800) 239-1103.
You have equity, you have plans, and you’re ready to build an ADU. Now the question is how to finance it. The two most common options are a HELOC (home equity line of credit) and a construction-to-permanent loan. They work very differently, and the right choice depends primarily on one thing: what rate is on your existing first mortgage.
HELOC for ADU Construction: How It Works
A HELOC is a revolving line of credit secured by your home equity. During the draw period (typically 10 years), you borrow only what you need, when you need it — and pay interest only on the outstanding balance. This structure is ideally suited to ADU construction where costs come in stages: permits and design, foundation, framing, electrical, finishes. You draw as each phase invoices rather than borrowing the full amount upfront. After the draw period, the HELOC converts to a repayment period where you pay principal and interest on the outstanding balance.
The biggest advantage of a HELOC: your existing first mortgage stays completely untouched. If you bought or refinanced between 2020 and 2022 at 2.5%–3.5%, a HELOC lets you fund a full ADU build without giving up that rate. On a $600,000 first mortgage, the difference between 3% and 7% is roughly $2,400/month. Preserving that rate while accessing a separate HELOC for the build is almost always the right financial move. HELOC rates are variable — they adjust with the market — but the total blended cost of a low-rate first plus a variable HELOC is typically far better than refinancing everything into one new loan at today’s rates.
Construction-to-Permanent Loan: How It Works
A construction loan funds the build through a series of draws as work is completed and inspected, then converts to a permanent mortgage at completion. Underwriting is done upfront based on the after-completion appraised value (ARV) — which can unlock more borrowing power than a HELOC based on current equity alone. The permanent loan that emerges at completion carries a fixed rate locked in at origination, giving long-term payment certainty. This is a single-close transaction: no second refinance needed when the ADU is done.
The primary downside is that a construction-to-permanent loan replaces your existing first mortgage. If you have a 3% rate on a $700,000 balance, converting that to a new 7% rate adds roughly $2,100/month to your costs — every month, for the life of the loan. That’s an expensive way to fund an ADU. Construction loans also require more upfront work: licensed general contractor, approved plans, lender-ordered inspections at each draw. For borrowers with limited current equity but strong after-completion value, however, the ARV underwriting can be the difference between being able to fund the project at all versus not.
Side-by-Side Decision Guide
| Situation | Best Option |
|---|---|
| Existing low mortgage rate (below 5%) | HELOC |
| Limited current equity but strong ARV | Construction loan |
| Phased or owner-managed construction | HELOC |
| Want fixed rate certainty for full project | Construction-to-perm |
| No existing mortgage or existing rate above 6% | Either — compare total cost |
I model both scenarios with current rates and your actual equity position before making a recommendation. Call (800) 239-1103 to compare your ADU financing options side by side.
Frequently Asked Questions — ADU Construction Loan vs HELOC California
Can I use a HELOC to fund an ADU if I already have a low mortgage rate?
Yes — and for most California homeowners with a sub-5% first mortgage, a HELOC is the right choice precisely because it leaves that first mortgage untouched. You borrow only what you need for the ADU build on a separate line of credit, paying interest only on what you draw. Your blended rate across both loans is almost always lower than refinancing everything into one new first mortgage at today’s rates. The only scenario where a construction-to-permanent loan is clearly better is when you have minimal current equity but strong after-completion value — the ARV underwriting in that case can unlock capital a HELOC cannot.
How much HELOC can I get to build an ADU in California?
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 availability. Even with a higher existing mortgage balance, Bay Area and Marin homeowners often have enough equity to fund a full ADU build ($150,000–$350,000 in most cases) without a cash-out refinance. For properties over $2M, I have access to jumbo HELOC products with higher CLTV limits than standard bank programs.
Can I refinance out of the HELOC into a fixed rate once the ADU is completed?
Yes — and this is a common strategy. Once the ADU is completed, permitted, and generating documented rental income, you can refinance both the first mortgage and HELOC into a single new first mortgage at a fixed rate. The post-construction appraised value (higher than before the ADU) improves your LTV, and the documented rental income improves your DTI — often resulting in better terms than you’d get during construction. Whether this makes sense depends entirely on where rates are when the ADU is completed. If rates have dropped from today, refinancing makes sense; if rates are similar or higher, staying with a low-rate first plus the HELOC may remain the better structure.
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
