The reason financing gets its own guide is simple: on most ADU budgets, the wrong loan costs more than the wrong finishes ever will. A homeowner who reprices a low first mortgage to pull cash can hand back years of the ADU's rental upside before the first tenant moves in. So before you fall for a rate, get your real number. Price your build with our ADU cost estimator and read the ranges on our ADU cost pages, then size the financing to that.
One note on what this page is. I build ADUs, I do not lend money, and I take no referral fees from anyone who does. Every rate and rule below is dated and linked to its own official source, because these numbers move. Everything here is current as of September 11, 2026.
The financing options, and where each one fits
There are really six paths most homeowners use. Here they are side by side, then one at a time with the honest math on when each is right and when it is a trap.
| Option | How it is secured | Typical rate (as of September 11, 2026) | Best for | The catch |
|---|---|---|---|---|
| HELOC | A second lien on your existing equity | ~7.26% to 7.29% variable | Drawing cash as the build hits milestones, while keeping your first mortgage | Variable rate, and you need real equity already |
| Home equity loan | A fixed second lien on your equity | ~7.35% fixed | A fixed lump sum when you know your number | Same equity requirement, less flexibility than a HELOC |
| Cash-out refinance | A new first mortgage replacing your current one | ~6%+ fixed (first-mortgage territory) | Homeowners with a high existing rate, or no first mortgage | Reprices your whole balance. Usually the wrong tool if your current rate is low |
| HomeStyle / CHOICERenovation | One loan underwritten on the as-completed value | Conventional first-mortgage rates | Equity-light recent buyers building on future value | More paperwork and a renovation-loan process, not a quick close |
| FHA 203(k) | An FHA loan bundling purchase or refi plus the work | FHA rates, low down payment | Low equity, and an attached ADU (203k ADU work must be attached) | Attached only, mortgage insurance, tighter rules |
| Construction-to-permanent | Draws against milestones, converting to a mortgage at completion | Higher than home-equity products | Ground-up detached builds that renovation limits do not fit | Draw schedule and inspections, higher rate, more moving parts |
Rate ranges reflect national averages as of September 11, 2026 and move weekly. HELOC average around 7.26% to 7.29%, fixed home equity around 7.35%, per Bankrate and heloccalculator.org surveys dated that week. Treat these as planning ranges, not a quote.
HELOC and home equity loan
Both borrow against the equity you already have, usually up to somewhere around 80% to 85% combined loan-to-value, and both leave your first mortgage alone. That last part is the whole point in this rate cycle. A HELOC runs variable (national average around 7.29% as of September 11, 2026) and lets you draw as the build progresses; a fixed home equity loan (around 7.35%) hands you a lump sum. The honest limitation is that you need real equity already, so this path is thin for anyone who bought recently.
Cash-out refinance, usually the wrong tool right now
This is the flagship mistake, so I will be blunt about it. A cash-out refinance replaces your entire first mortgage with a new, larger one at today's rate. If you are holding a low-rate pandemic-era mortgage, pulling ADU money this way reprices your whole balance from that low rate up to roughly 6% or more as of September 11, 2026, which can cost you far more over time than the ADU earns. It makes sense in exactly two cases: you already carry a high rate, or you own the home outright. Otherwise a home-equity second or a renovation loan is cheaper, and it is not close.
Renovation loans that can fund a new ADU: HomeStyle and CHOICERenovation
Renovation loans are the underused answer for equity-light owners, because they underwrite on the as-completed value rather than what your home is worth today. Fannie Mae's HomeStyle Renovation and Freddie Mac's CHOICERenovation mortgages both finance a purchase or refinance plus the work in a single loan. HUD's own program-comparison fact sheet confirms HomeStyle can finance construction of accessory dwelling units, and Freddie's ADU fact sheet (dated February 2026) says borrowers can use CHOICERenovation to construct a new ADU or renovate an existing one. The tradeoff is process: these are more paperwork than a HELOC and they close slower.
FHA 203(k)
The FHA 203(k) bundles a purchase or refinance with the renovation into one FHA loan, which is a real help for low-equity buyers. The catch specific to ADUs is that HUD's fact sheet specifies the 203(k) ADU work must be attached, so this path does not cover a detached backyard build. A Standard 203(k) does let you count 50% of the projected rent from a new attached ADU toward qualifying, under FHA Mortgagee Letter 2023-17.
Construction and construction-to-permanent loans
For a ground-up detached ADU that renovation-loan limits will not fit, a construction or construction-to-permanent loan is the standard answer. It disburses in draws against inspected milestones, then converts to a normal mortgage at completion. The rate runs higher than home-equity products, but the draw structure is also a consumer protection, which I come back to below.
The rental-income rule that changed who qualifies
If you take one thing from this page, take this. Over the last two years, all three major channels rewrote their rules so a homeowner can count ADU rental income toward qualifying on a one-unit primary residence. That is new, and it moves the line on who can get approved at all. The shape is consistent across the three: the income is capped at 30% of your qualifying income, and lenders generally count 75% of the market rent (50% for a brand-new attached ADU under FHA's construction path). The details differ, so here is each one with its citation.
FHA
Under Mortgagee Letter 2023-17, effective October 16, 2023, FHA lets you count 75% of the estimated rent from an existing ADU on the subject property toward effective income, or 50% of the projected rent from a new attached ADU built with a Standard 203(k). Either way it is capped at 30% of your total monthly effective income.
Fannie Mae
Fannie's Selling Guide topic B3-3.8-01, amended by announcement SEL-2025-08, now allows ADU rental income on a one-unit principal residence. It is limited to purchase and limited cash-out refinance (a true cash-out is not eligible), counts income from only one ADU, caps it at 30% of qualifying income, and requires landlord education for a purchase unless you have prior landlord experience. It took effect for manual underwriting on October 8, 2025, with automated eligibility in Desktop Underwriter version 12.1 rolling out during 2026.
Freddie Mac
Freddie's Guide Section 5306.1 allows rental income from an ADU on a subject one-unit primary residence. Per Freddie's ADU fact sheet dated February 2026, borrowers can finance, refinance, build or renovate an ADU and use the rental income when the requirements are met, with a 75% factor commonly applied and the same 30% cap.
None of this is a promise you will qualify. It is the set of rules your lender is working from, so print the citations and bring them to the conversation. Underwriters do not all apply new guidance at the same speed.
The honest math, and one protection worth knowing
The rate environment as of September 11, 2026 is the backdrop for all of this. HELOC and home-equity averages sit around 7.26% to 7.35%, which is actually the lowest HELOC has been in years. Thirty-year first mortgages remain in the 6% range, higher than home-equity products in this cycle, which is exactly why refinancing a low first mortgage to fund an ADU is usually a losing trade. Construction loans run higher than all of them.
Here is the protection most homeowners never think about until it is too late. A construction loan's draw schedule ties each disbursement to an inspected, completed milestone, so the money stays aligned with actual progress. When homeowners instead pay a contractor large sums upfront, they carry the risk of the work falling behind or the contractor walking. That draw structure is the safeguard the homeowners who paid collapsed builders upfront did not have. If you are choosing a builder, our ADU builder guides walk the license-verification side of the same problem.
What about grants?
Grants get more search attention than they deserve, because the biggest one is gone. California's statewide CalHFA ADU grant has been closed to new applications since December 28, 2023, and CalHFA itself warns that anyone promising to get you that grant is running a scam. The live programs are local and state-level now, and worth knowing if you are in the right place. I cover both in detail:
- The California ADU grant, and the live California alternatives (including San Diego's construction-to-permanent program).
- ADU grants by state: Massachusetts, Boston, Colorado, Portland, and the states where the "grant" is a myth.
Frequently asked questions
What is the best way to finance an ADU?
There is no single best way, only the one that fits your equity, your first-mortgage rate and your timeline. If you already own the home and hold a low first mortgage, a HELOC or home equity loan usually wins because it leaves that low rate alone. If you are equity-light or buying and adding the ADU at once, a renovation loan or construction-to-permanent that appraises on the finished value tends to fit better. As of September 11, 2026, cash-out refinancing is usually the wrong tool for anyone sitting on a low-rate first mortgage.
Can I use future ADU rent to qualify for a loan?
Often yes, and this is the biggest shift of the last two years. FHA, Fannie Mae and Freddie Mac all now let a homeowner count ADU rental income toward qualifying on a one-unit primary residence, within limits: the income is capped at 30% of your qualifying income, and lenders typically count 75% of the market rent. The exact rules differ by channel, so read the rental-income section above and take the citations to your lender.
Is a cash-out refinance a good way to pay for an ADU?
Usually not, if you are holding a low-rate first mortgage. A cash-out refinance replaces your entire mortgage at today's rate, so pulling ADU money that way reprices your whole balance from, say, a pandemic-era rate up to roughly 6% or more as of September 11, 2026. It makes sense mainly for homeowners who already carry a high rate, or who own the home free and clear. Otherwise a home-equity second or a renovation loan is almost always cheaper.
Are there grants to help pay for an ADU?
A few real programs exist, but far fewer than the internet implies, and California's statewide CalHFA grant has been closed since December 28, 2023. Live help is mostly local and state-specific now: San Diego, Massachusetts, Boston, Colorado and Portland all run active programs with their own rules. We cover the closed California grant and the live California alternatives on the CalHFA page, and the by-state grant landscape on the ADU grants page.
How much does an ADU cost to build?
Enough that the financing decision matters, which is the whole reason this page exists. Costs swing widely by city, size, type and finish, so a national average is close to useless for planning your loan. Price your own build with our estimator and read the real ranges on our ADU cost pages, then size the financing to that number rather than to a figure you read somewhere.
If I were doing this today, I would pin my real build number first, check whether the ADU rental-income rule gets me over the qualifying line, and only then shop the loan. Start with a cost estimate for your lot.
Education, not financial advice. I am a builder, not a lender or advisor. Program terms and rates move, so confirm every figure against the official source linked next to it before you count on it.