California mortgage guide
ADU Financing in California: HELOC, Cash-Out, Construction, and Renovation Loans Compared
In this guide
Most California accessory dwelling units are financed four ways: a home equity line or loan that leaves the first mortgage untouched, a cash-out refinance that replaces it, a construction loan that pays the builder in stages, or a renovation loan that funds the build inside a purchase or refinance.
Key numbers
| Item | Figure | Source |
|---|---|---|
| Cap on ADU rent used to qualify (Fannie Mae) | Rental income from an ADU cannot exceed 30% of the total income used to qualify | Fannie Mae — ADU income flexibilities (November 14, 2025) |
| Appraisal requirement for ADU rent | A Single-Family Comparable Rent Schedule (Form 1007) must be included in the appraisal | Fannie Mae — ADU income flexibilities |
| New landlords | With less than 12 months of property-management experience and a housing payment, qualifying ADU rent cannot exceed the housing payment | Fannie Mae — ADU income flexibilities |
| Vacancy adjustment in Fannie Mae's own sample | Market rent is reduced by 25% before it is used to qualify ($1,400 × 0.75 = $1,050) | Fannie Mae — ADU income flexibilities, sample scenario 1 |
| Property-tax effect of building | The new construction is assessed at its added value and a supplemental bill follows; the existing home keeps its Prop 13 base | California BOE — Supplemental Assessment |
Who each path fits — and who should look elsewhere
Home equity line or loan fits when your first mortgage carries a rate you want to keep and your home has enough equity above the existing loan. You draw only what the build needs, and the first mortgage — often the cheapest debt a California household holds — is never touched.
Cash-out refinance fits when your existing rate is at or above today's rates, or when you need the ADU money plus other debt consolidation in one loan. Look elsewhere if your current rate is well below market: a cash-out refinance reprices every dollar you owe, not just the new money for the ADU. And if you were counting on rent from an existing ADU to qualify, a cash-out refinance cannot use it under Fannie Mae’s rules. On a large existing balance, that repricing can cost more over the loan's life than the ADU itself.
Construction loan fits a larger detached build when current equity is thin, because the loan is sized against the completed project and funded in draws as work passes inspection. Renovation loans — FHA 203(k) and Fannie Mae HomeStyle-type programs — fit when the ADU is part of buying the home or refinancing it at the same time, with the contractor paid from an escrowed renovation account.
Look elsewhere entirely if the project only works with rent you have not collected yet. On a standard loan, rent from an ADU that does not exist yet is generally not counted to help you qualify. If the file needs that future rent to pass, the project is not ready to finance — build the plan around income and equity you have today.
Requirements: program rules and lender overlays
Program rules — using rent from an existing ADU. Fannie Mae allows rental income from an ADU on a one-unit property to help you qualify on a purchase or a limited cash-out refinance only — not on a cash-out refinance — under its standard rental-income guidelines. The appraisal must include a Form 1007 rent schedule specific to the ADU; if the appraiser cannot find ADU rentals as comparables, similar non-ADU rentals may be used with adjustments. Two caps apply: the ADU rent used cannot exceed 30% of the total income used to qualify, and a borrower with less than 12 months of property-management experience who has a housing payment cannot use rent above that housing payment.
Program rules — permits come first. Every path requires an approved, permitted project. California state ADU law — the Government Code sections the California Department of Housing and Community Development oversees, renumbered by Senate Bill 477 in 2024 — limits how far a city or county can go in blocking ADUs, but the permit, plans, and fees are still local. A lender funds a permitted project, not an idea: expect to show approved plans and a signed contractor agreement before draws begin.
Lender overlays. How much of the project cost a lender will advance before work is complete, how much contingency reserve is required, and whether a garage conversion qualifies the same way as a detached unit are lender-level decisions. Two lenders can look at the same permitted project and offer different draw schedules — compare the draw schedule and the reserve requirements, not just the rate.
What an ADU project costs beyond the loan
| Cost | How it works |
|---|---|
| Design, plans, and permits | Paid to your designer/architect and your city or county. Get the local fee schedule for your parcel before you size the loan — fees are set locally and vary widely. |
| Construction draws and interest during the build | Construction and renovation loans fund in stages; interest accrues on what has been drawn. A slow permit or build raises the interest carried before the unit can be occupied or rented. |
| Supplemental property tax | Completed new construction is assessed at its added value. The supplemental bill is prorated from the first of the month after completion to June 30; your ongoing tax bill then includes the ADU's added value on top of your home's existing Prop 13 base. |
| Insurance | The completed ADU must be added to your homeowners policy; a rented unit can change the policy structure your insurer requires. Price this before the build finishes, not after. |
| Utility connections | Separate metering or capacity upgrades are priced by your utility and city; they belong in the project budget from the start. |
Grant money deserves a caution. State and local ADU grant and incentive programs open and close as funding rounds come and go; a program described on a builder's website may not be accepting applications today. Treat any grant as a bonus you check with the administering agency directly — never as money the loan depends on.
California specifics
Three California rules shape ADU financing. First, state ADU law sets the floor for what local agencies must allow, and the California Department of Housing and Community Development reviews local ordinances against it — a denial that contradicts state law is worth challenging before you redesign the project. Second, a junior ADU (JADU) is a smaller unit created within the existing home; it finances the same ways but at a smaller project size. Third, the tax treatment splits the property in two: the original home keeps its Prop 13 base year value, and only the ADU's added value is newly assessed, with a supplemental bill for the first partial year.
Worked example: counting rent from an existing ADU
A couple buys a one-unit home with a permitted ADU over the garage. A tenant has already signed a lease at $1,800 a month. The buyers earn $6,500 a month, their total housing payment (principal, interest, taxes, insurance) is $1,200, and they have never been landlords.
- Step 1 — vacancy adjustment: $1,800 × 0.75 = $1,350 a month.
- Step 2 — the 30% cap: total income used to qualify if the full $1,350 counted would be $6,500 + $1,350 = $7,850; 30% of $7,850 is $2,355. The $1,350 is under the cap.
- Step 3 — the new-landlord cap: with less than 12 months of property-management experience and a $1,200 housing payment, qualifying rent cannot exceed $1,200.
- Result: $1,200 a month of ADU rent can be used — not the $1,800 on the lease.
That $600 difference is exactly where ADU budgets break. Plan the purchase on the $1,200 figure; treat anything above it as cushion, not as qualifying income.
How ADU financing proceeds
- Permit path first. Establish that your parcel and design can be permitted, and get the local fee schedule.
- Choose the financing path. Compare keeping your first mortgage (home equity) against replacing it (cash-out) against funding the build itself (construction or renovation loan) — using the rate on your current mortgage as the deciding input.
- Apply and document. Income, assets, the existing mortgage, plans, permits, and the contractor agreement. You receive a Loan Estimate for the new loan within three business days of a completed application.
- Appraisal. For an existing ADU whose rent you want counted, the appraisal must include the Form 1007 rent schedule. For a build, the appraisal addresses the completed project.
- Close and draw. Equity loans fund against the current home; construction and renovation loans release money in stages as work is completed and inspected.
- Finish the paperwork that outlives the loan. Final permits signed off, insurance updated to include the unit, and the supplemental tax bill for the added value budgeted.
Common mistakes
- Refinancing out of a low first-mortgage rate to fund a modest build. If your current balance is $600,000, a cash-out refinance reprices all $600,000 — plus the ADU money — at today's rate. Price the home-equity path on the same project before you touch the first mortgage.
- Counting full future rent. Fannie Mae reduces market rent by 25% in its own sample, caps ADU rent at 30% of qualifying income, and caps new landlords at their housing payment. Rent from an ADU you have not built is generally not counted at all on a standard loan.
- Budgeting the build and forgetting the tax step-up. The ADU's added value is assessed when construction completes, and the supplemental bill arrives for the partial year. It surprises owners who assumed Prop 13 froze their whole tax bill.
- Starting work before the loan structure allows it. Renovation and construction loans pay for work done after closing under the program's draw rules. Work started early can be work the loan will not reimburse.
Questions homeowners ask
Can rent from an ADU help me qualify for the loan?
Yes, if the ADU already exists. Fannie Mae counts ADU rent with a Form 1007 rent schedule in the appraisal, capped at 30% of the income used to qualify, and capped at your housing payment if you have less than 12 months of landlord experience.
Can I count rent from the ADU I am about to build?
Generally not on a standard loan. Projected rent from an unbuilt unit is not the same as documented rent from an existing one — ask specifically about renovation-program rules before planning around future rent.
Should I use a HELOC or a cash-out refinance?
Start with the rate on your current mortgage. If it is well below today's rates, a home equity line or loan usually preserves more value because only the ADU money carries the new rate. If your current rate is already at or above market, one cash-out loan can be simpler.
Are there California grants for ADUs?
State and local programs have offered grants and incentives, but rounds open and close with funding. Check the current status with the administering agency — do not size a loan assuming grant money that is not currently accepting applications.
Will building an ADU raise my property taxes?
Yes, on the added value only. The assessor values the new construction, a supplemental bill covers the first partial year, and your original home keeps its Prop 13 base.
What is the difference between an ADU and a JADU?
An ADU is a complete secondary unit, attached or detached. A junior ADU is a smaller unit created within the existing home's walls. Both are covered by California's ADU law; the financing paths are the same, at different project sizes.
Sources
- Fannie Mae — Accessory Dwelling Unit Income and HomeReady Boarder Income Flexibilities (November 14, 2025; fetched October 14, 2026).
- California Department of Housing and Community Development — Accessory Dwelling Units, including the Senate Bill 477 renumbering of the Government Code ADU sections (fetched October 14, 2026).
- California State Board of Equalization — Supplemental Assessment (fetched October 14, 2026).
Last reviewed October 15, 2026. Questions: call 415-297-6703 or use the contact page.
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