The most common reason Southern California homeowners don't build an ADU isn't zoning, permits, or contractors — it's not knowing how to pay for it. The good news: there are more financing options available today than at any point in the past, including programs specifically designed for ADU construction. Here is a plain-English breakdown of every option, who it works for, and what it actually costs.

First: Know Your Numbers

Before choosing a financing path, you need two numbers:

1. Your home's current market value — get a rough estimate from Zillow or Redfin, or ask a local agent for a quick opinion
2. Your remaining mortgage balance — check your last statement

The difference between those two numbers is your equity. Most ADU financing options are equity-based, so the more equity you have, the more options you have and the better the terms.

A homeowner in LA County who bought in 2018 and has been paying down their mortgage likely has $300,000–$600,000 in equity. That's more than enough to finance most ADU projects.

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Option 1: Home Equity Line of Credit (HELOC)

A HELOC is a revolving line of credit secured by your home equity. You draw from it as needed during construction and pay interest only on what you've used.

How it works:

• Lender approves a credit line (typically up to 85–90% of your home's value minus your mortgage balance)
• You draw funds as construction bills come in
• Interest-only payments during the draw period (usually 10 years)
• Principal + interest payments during the repayment period (usually 20 years)

Current rates (2026): Variable, typically Prime + 0.5–1.5%. With Prime at 7.5%, expect 8–9% on a HELOC.

Example: $200,000 HELOC at 8.5% — interest-only payment during construction is roughly $1,417/month. Once the ADU is rented at $2,000/month, the rental income more than covers the payment.

Best for: Homeowners with significant equity who want flexibility. You only pay interest on what you draw, so if construction takes 10 months, you're not paying interest on the full amount from day one.

Watch out for: Variable rates. If rates rise significantly during your draw period, your payments increase. Some lenders also freeze or reduce HELOCs if home values drop.

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Option 2: Cash-Out Refinance

A cash-out refinance replaces your existing mortgage with a new, larger mortgage and gives you the difference in cash.

How it works:

• You refinance your home for more than you owe
• The difference (up to 80% of your home's value) comes to you as cash
• You now have one mortgage at the new, higher balance

Example: Home worth $900,000, current mortgage $400,000. Cash-out refi to 80% LTV = $720,000 new mortgage. You receive $320,000 cash. Use $200,000 for the ADU, keep $120,000 in reserve.

Current rates (2026): 30-year fixed rates are in the 6.5–7.5% range depending on credit and LTV.

Best for: Homeowners who currently have a mortgage rate above today's rates (rare in 2026, but some 2022–2023 buyers are in this position), or those who want a single fixed payment rather than a variable line of credit.

Watch out for: If your current mortgage rate is below 6%, a cash-out refi means giving up that rate on your entire balance — not just the new money. Run the math carefully. For most homeowners who locked in rates below 5%, a HELOC or second mortgage is almost always better than a cash-out refi.

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Option 3: Home Equity Loan (Second Mortgage)

A home equity loan is a lump-sum loan secured by your equity, separate from your first mortgage. Unlike a HELOC, it has a fixed rate and fixed monthly payment.

How it works:

• Lender approves a fixed loan amount (typically up to 85% of home value minus mortgage balance)
• You receive the full amount upfront
• Fixed monthly payments over 10–20 years

Current rates (2026): Fixed, typically 8–10% depending on credit and LTV.

Best for: Homeowners who want the predictability of a fixed payment and don't want to risk a variable rate. Good if you have a low first mortgage rate you want to keep.

Watch out for: You're paying interest on the full amount from day one, even if construction takes 12 months to complete. A HELOC is usually more cost-efficient during construction; a home equity loan makes more sense once the ADU is built and generating income.

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Option 4: Construction Loan

A construction loan is a short-term loan specifically designed to fund construction. It converts to a permanent mortgage (or is paid off) when construction is complete.

How it works:

• Lender approves the loan based on the projected value of the completed ADU
• Funds are disbursed in draws as construction milestones are reached
• Interest-only during construction (typically 12–18 months)
• Converts to a permanent loan or is refinanced at completion

Current rates (2026): Construction loan rates are typically 1–2% above standard mortgage rates — expect 8–9.5%.

Best for: Homeowners who don't have enough equity for a HELOC or home equity loan, or who are building a larger, more expensive ADU and need a loan sized to the completed value rather than current equity.

Watch out for: More complex underwriting, higher rates, and the need to refinance at completion (which means closing costs twice). Also requires a detailed construction contract and budget upfront.

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Option 5: CalHFA ADU Grant Program

The California Housing Finance Agency (CalHFA) has offered grant programs specifically for ADU pre-development costs — design, permits, and site prep. These are not construction loans; they cover the upfront costs before construction begins.

How it works:

• Grants of up to $40,000 for pre-development costs (design, permits, soils reports, utility connections)
• Available to owner-occupants in California
• Income limits apply (typically 80–120% of Area Median Income)
• Grant is forgiven after a set period if you remain the owner-occupant

Availability: CalHFA ADU grant programs have had limited funding and periodic pauses. Check calhfa.ca.gov for current availability. Some local jurisdictions (LA County, City of San Diego) have run parallel programs with their own funding.

Best for: Homeowners who qualify on income and want to reduce out-of-pocket costs for the design and permit phase — which can run $20,000–$40,000 before a shovel hits the ground.

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Option 6: ADU-Specific Lenders

A growing number of lenders now offer loan products specifically designed for ADU construction. These programs underwrite the loan based on the projected rental income of the completed ADU, not just your current equity.

Notable programs:

• Mosaic and RenoFi offer renovation loans that factor in the after-renovation value of your property
• Some credit unions in California have developed ADU-specific products with streamlined underwriting
• Several community development financial institutions (CDFIs) offer ADU loans in lower-income areas with below-market rates

Best for: Homeowners with moderate equity who might not qualify for a large enough HELOC or home equity loan based on current value alone.

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Option 7: Cash

If you have savings, investments, or retirement funds you're willing to deploy, paying cash eliminates interest costs entirely and simplifies the process significantly.

The math: A $200,000 ADU financed at 8.5% over 20 years costs roughly $124,000 in interest. Paying cash saves that entire amount — and the ADU's rental income becomes pure cash flow from day one.

Watch out for: Liquidity. Tying up $200,000 in a real estate project means that money isn't available for emergencies or other opportunities. Most financial advisors suggest keeping 6–12 months of expenses liquid even after a major investment.

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Which Option Is Right for You?

Situation	Best Option
Strong equity, current mortgage rate below 5%	HELOC or home equity loan
Current mortgage rate above 6.5%	Cash-out refinance
Limited equity, strong income	Construction loan or ADU-specific lender
Qualify on income, need help with pre-dev costs	CalHFA grant + HELOC
Have the cash	Pay cash, keep a reserve

The Real Question: Does the Math Work?

For most Southern California homeowners, the answer is yes — often comfortably. A $200,000 ADU financed at 8.5% on a HELOC costs roughly $1,417/month in interest during construction. Once rented at $2,000–$2,500/month, the rental income covers the payment with $600–$1,000/month left over — and that spread grows as you pay down principal.

The key is going in with accurate numbers: realistic construction cost, realistic rental income for your specific neighborhood, and a financing structure that fits your balance sheet.

Our free ADU Site Analysis includes a financing overview for your specific situation — what your equity supports, which programs you likely qualify for, and what the monthly cash flow looks like after debt service. It's the fastest way to go from "I think I can afford this" to "here's exactly how I'm going to pay for it."