How to Finance an ADU: 7 Options Compared

By ADU Scope editorial team · Last verified: October 2026
How to finance an ADU comes down to one question: do you have a low-rate mortgage worth keeping? If so, borrow against your equity with a HELOC or home equity loan and leave the first mortgage alone. If not, a cash-out refinance or a renovation mortgage can work. In general, cash is cheapest, and a home equity investment is usually the most expensive. The Freddie Mac 30-year average was 7.28% as of Oct 1, 2026, so replacing a mortgage far below that rate is costly.

Overall, costs run high. A 2021 Terner Center statewide owner survey reported a median California ADU cost of about $150,000, per its summary. For a city-by-city view, see our guide to how much an ADU costs in California.

This article is general information, not financial advice. Rates, limits and eligibility change, and every example below is hypothetical. Confirm figures with at least three lenders.

How to finance an ADU: the seven options at a glance

To start, here is the map. Each route is covered below, and most have a dedicated guide in this series.

Option	Where the money comes from	Rate type	Main risk	Best for
1. Cash savings	Your own funds	None	Drains your emergency reserves	Owners with real cash cushion left after building
2. HELOC or home equity loan	Second loan secured by your home	HELOC usually variable; home equity loan fixed or adjustable	Payments can rise; the home secures the debt	Owners with equity and a low-rate first mortgage
3. Cash-out refinance	New, larger first mortgage	Usually fixed	Resets your whole balance to today’s rate	Owners whose current rate is near or above market
4. Renovation mortgage	One loan based on as-completed value	Varies by program	Contractor approval and heavy paperwork	Buyers adding an ADU, or owners with little equity
5. ADU construction loan	Staged draws during the build	Varies by lender	Terms differ widely; interest accrues during the build	Owners whose lender offers a build-then-convert loan
6. Personal loan	Unsecured loan, no lien on the home	Usually fixed	High payment from short terms and higher rates	Small projects, or owners with little equity
7. Home equity investment	Cash now for a share of future home value	No monthly interest	Very high effective cost; possible forced sale	Last resort when no loan fits

How to finance an ADU: who should use what

Therefore, do not shop for the “best” product in the abstract. Match the product to your situation, then compare written quotes.

Low-rate mortgage and plenty of equity: start with a HELOC or home equity loan. Our HELOC guide shows how the payments behave.
Mortgage rate at or above market: price a cash-out refinance next to a home equity loan. Our cash-out refinance vs HELOC comparison includes a break-even test.
Buying a home, or little equity: price a renovation mortgage first, because it can lend against the finished value.
Cash-rich owner: pay cash, but keep a reserve, because cost overruns happen.
Small project and no equity: a personal loan can work if the payment fits.
No loan fits and you cannot carry payments: only then look at a home equity investment, and read the contract with a professional.

How to finance an ADU with cash or home equity

Cash carries no interest and no approval process. However, it leaves you thin if the build runs over. The Terner Center reports that most owners who built an ADU used cash plus a mortgage, with home equity loans and cash-out refinances the most common mortgage types.

How to finance an ADU with a HELOC or home equity loan

The CFPB describes a HELOC as a line you can draw on repeatedly. Draws typically run about 10 years. Repayment then runs about 10 to 20 years. HELOCs usually carry variable rates, so payments can change from month to month. The lender can also freeze the line if your home value falls or your finances worsen.

A home equity loan instead pays out a lump sum at a fixed or adjustable rate. Both products are second mortgages, so you pay them on top of your first mortgage. If you fall behind, you could lose your home.

The CFPB notes that home equity lending lets you use your equity without replacing a low-rate mortgage with a higher-rate cash-out refinance. That is the main reason this route wins for owners with old, cheap mortgages. Read our HELOC for an ADU guide for the payment math, and see how much equity you need in our equity requirements article.

How to finance an ADU with a cash-out refinance

A cash-out refinance replaces your mortgage with a bigger one and hands you the difference. Also, you get one loan and often a fixed rate. However, the cost is that your whole balance moves to the new rate. Freddie Mac reported averages of 7.28% for 30-year and 6.60% for 15-year fixed loans as of Oct 1, 2026. In short, those are survey averages, not quotes for cash-out loans.

For example, here is a quick test. Ask for a cash-out quote and a HELOC quote for the same cash amount. Then compare the total monthly payment and the closing costs over the years you expect to keep each loan. If your current rate is well below market, the refinance usually loses. If it is close to or above market, the refinance can win because you get a fixed payment.

How to finance an ADU with a renovation mortgage or construction loan

How to finance an ADU with a renovation mortgage

Fannie Mae’s HomeStyle Renovation lists accessory dwelling units, such as in-law suites, among eligible projects. Per Fannie Mae, maximum LTV can reach 97%. For purchases, the total loan can be up to 75% of the lower of purchase price plus renovation costs or the as-completed appraised value. For a refinance of a home you own, ask the lender which rules apply.

FHA 203(k) is the other main program. HUD says the Limited version covers up to $75,000 of non-structural work. The Standard version allows structural additions, requires at least $5,000 of rehabilitation and a HUD-approved consultant, and must stay within FHA mortgage limits. HUD’s 2023 policy update, as we read it, treats ADUs as eligible improvements. Look up your county’s FHA limit in HUD’s own lookup tool, because we have not verified current figures.

Freddie Mac’s CHOICERenovation exists too, but its fact sheet does not mention ADUs. Ask the lender whether your scope qualifies.

How to finance an ADU with a construction loan

For instance, some lenders release money in stages during the build, then convert the loan to a permanent mortgage or require a refinance. Terms vary widely, and we found no official data on typical rates or limits. Our guide to ADU construction loans lists what to ask. Also compare the draw schedule with your contractor’s payment schedule.

Can rental income help you qualify?

In some cases, yes. Under FHA policy as summarized from HUD’s 2023 notice, ADU income can count as effective income, capped at 30% of the total income used to qualify. Borrowers without rental history can use an appraiser’s rent schedule. In addition, Fannie Mae’s rules differ by loan type, so ask the lender. Our rental income and qualification guide goes deeper.

Personal loan for an ADU: costly, but useful in narrow cases

A personal loan is unsecured, so your home is not collateral. It also adds no lien on your home. However, the trade-off is payment size. Terms are usually shorter than mortgage terms, and unsecured rates are usually higher. The Federal Reserve’s G.19 release put the average 24-month personal loan rate at commercial banks near 11.86% for Q2 2026, per a summary of that release.

Below, hypothetical rates apply to a $150,000 loan. The mortgage-style line is the Freddie Mac 30-year average, shown only for contrast.

Hypothetical $150,000 loan	Monthly payment	Total interest
Mortgage-style, 7.28%, 30 years	$1,026.32	$219,475
Personal loan, 10%, 7 years	$2,490.18	$59,175
Personal loan, 12%, 5 years	$3,336.67	$50,200

Overall, the personal loan costs less interest. However, the payment starts in month one, before the ADU earns any rent. For a smaller project the numbers look better: $40,000 at a hypothetical 10% over 5 years costs $849.88 a month. Lenders may cap loan amounts, so ask for each maximum, the APR and any origination fee. Do not stack a personal loan on top of another loan without recomputing your total obligations.

Home equity investments: the last resort

The CFPB calls these home equity contracts. You get cash now, and the investor takes a share of your home’s future value. There are no monthly payments, but the cost can be steep. Per the CFPB’s January 2025 market overview, terms typically run 10 to 30 years and fees run about 3% to 5%. The investor’s claim grew roughly 19.5% to 22% a year in early years under most scenarios. Its example: $50,000 on a $500,000 home could require $68,045 to $71,538 after three years.

You repay in one lump sum, so you may have to sell or refinance. For that reason, most owners should exhaust loan options first. Our home equity investment vs HELOC comparison covers the details. Moreover, grants are rare: the CalHFA ADU grant window that opened in December 2023 ran out of funds, and we could not verify a later round. See our California ADU grants guide for updates.

Before you borrow: three checks

Total your project cost with a contingency. Our ADU budget breakdown helps, and the cheapest way to build an ADU shows where to trim.
Stress-test the payment. Ask what happens if a variable rate rises, and what the payment is once repayment starts.
Plan for tax. A new ADU can raise your California property tax, as we explain in our ADU property tax guide.

Finally, compare lenders on fees as well as rates. Our guide to choosing an ADU lender has a checklist.

Frequently asked questions

What is the cheapest way to finance an ADU?

First, cash has no interest. With borrowing, keeping a low-rate first mortgage and adding a HELOC or home equity loan is often cheaper than refinancing, but compare quotes.

Is a HELOC rate fixed?

In most cases, no. Some lenders let you convert part of the balance to a fixed rate, which the CFPB says is usually higher than the variable rate.

Are home equity investments safe?

In short, they carry high effective costs and the risk of a forced sale. Have a professional read the contract before you sign.