Guide
How to finance an ADU
Very few people write a $250k check. Here are the ways homeowners actually fund ADU projects, roughly in order of how often they're used, with the honest trade-offs of each.
1. Home equity: HELOC or home equity loan
The workhorse of ADU financing. If you've owned your home for a while, you likely have equity to borrow against.
- HELOC(line of credit): draw as you pay the builder, pay interest only on what you've drawn. Rates float. Ideal for projects with staged payments.
- Home equity loan: a fixed lump sum at a fixed rate. Simpler, but you pay interest on the full amount from day one.
Most lenders cap combined loan-to-value around 80–90%. The big limitation: the loan is sized on your home's current value, not the value after the ADU exists.
2. Cash-out refinance
Replace your mortgage with a bigger one and take the difference in cash. This made enormous sense when rates were falling; it makes much less sense if your existing mortgage rate is lower than today's; you'd be repricing your whole loan to fund the project. Run the blended-rate math before choosing this over a HELOC.
3. Renovation loans that count the future value
A small but important category: loans underwritten against the home's after-renovation value, which solves the “not enough equity yet” problem for newer owners.
- Fannie Mae HomeStyle and Freddie Mac CHOICERenovation: conventional renovation mortgages that can fund an ADU.
- FHA 203(k): the FHA renovation loan, with more paperwork and mortgage insurance, but accessible credit requirements. FHA also now counts projected ADU rental income toward qualifying income in some cases, a meaningful 2023-era change.
4. Construction and ADU-specific loans
Ground-up detached ADUs sometimes use a construction loan that converts to permanent financing when the unit is done. A growing set of lenders and fintechs offer ADU-specific products that underwrite against future value and projected rent. Terms vary widely; compare against a plain HELOC before paying for novelty.
5. State and local incentive programs
Several states and cities have run ADU grant or subsidized-loan programs: California's CalHFA ADU grant (periodically funded and exhausted), plus programs in cities and counties from Santa Cruz to Seattle, and pilot programs elsewhere. These come and go with budget cycles, so check your state housing agency and your city's planning pagesfor what's currently open. Some cities also waive permit or impact fees for deed-restricted affordable ADUs, effectively a five-figure subsidy.
Choosing between them
| Situation | Usually the best fit |
|---|---|
| Lots of equity, low existing mortgage rate | HELOC or home equity loan |
| Little equity, bought recently | Renovation loan (HomeStyle / CHOICERenovation / 203k) |
| High existing mortgage rate | Cash-out refi (run the math), or HELOC |
| Large detached new build | Construction-to-permanent loan |
| Income-qualified / affordable unit | Check state & local grant programs first |
Practical advice
- Get your realistic total cost first (including fees, utilities, and contingency), then shop financing for that number, not the builder's base price.
- Talk to at least one local credit union. They're often the most flexible on ADU appraisals.
- If rental income is part of your plan, ask the lender whether they count projected ADU rent toward qualification; policies differ.
- Confirm the rules before borrowing: your city's official ADU regulations determine what you can actually build.