How to Finance an ADU: HELOCs, Renovation Loans & What Actually Works

The uncomfortable truth about ADU financing is that there's no such thing as an "ADU loan" in the way there's a car loan or a mortgage. You're financing a six-figure construction project, and lenders make you assemble the money from products designed for other things. Here are the paths that actually work, roughly in the order most homeowners should consider them.

Home equity: the workhorse

If you've owned your home for a while, your equity is usually the cheapest money available. A HELOC (home equity line of credit) lets you draw funds as construction bills arrive and pay interest only on what you've used — a good match for a project billed in stages. A home equity loan gives you a fixed lump sum at a fixed rate, which suits people who want payment certainty over flexibility. Most lenders let you borrow up to 80–85% of your home's value minus what you owe. The risk is the same for both: your house secures the debt, so a failed project doesn't make the payments go away.

Cash-out refinance: sometimes right, often not

A cash-out refi replaces your entire mortgage with a bigger one and hands you the difference. Whether this makes sense depends almost entirely on your current rate: if you locked a low rate years ago, refinancing the whole balance at today's rates to fund an ADU can cost far more over time than a HELOC on top of your existing loan. Run the total-interest math on both before deciding — this is the single most expensive mistake in ADU financing.

Renovation and construction loans: for equity-poor owners

If you bought recently and equity is thin, renovation loans (like FHA 203(k) or Fannie Mae HomeStyle) are built for your situation: they lend against the value your home will have after the ADU is built, not its value today. Some lenders now explicitly count projected ADU rental income when qualifying you, which can meaningfully raise what you can borrow. The tradeoff is process: more paperwork, lender-approved contractors, draw inspections at each stage. Slower, but it makes projects possible that equity alone can't fund.

Grants and local programs: check, but don't plan around them

California has periodically funded an ADU grant program (historically up to $40,000 toward pre-construction costs), and some cities and counties run their own incentive or low-interest loan programs. These come and go as funding cycles open and close — worth thirty minutes of checking your state housing agency and city website before you borrow a dollar, but don't build your budget around money that may not be available when you apply.

What lenders will ask that you should ask first

Before any application, know your project number. Lenders want a real budget, not a guess — and padding matters, because the classic ADU financing failure is borrowing exactly the contractor's bid and having nothing left when utility trenching runs long. Budget the full itemized cost plus a 10–15% contingency, then borrow against that. Our cost calculator gives you the itemized starting point, and our city guides show the permit fees lenders often forget to mention.

Run the numbers for your project

Every project is different — size, scope, and city move the total by six figures. Get an itemized estimate in under a minute:

Written and reviewed by ADUCostGuide. Cost figures reflect 2026 data and typical projects; rules and prices vary by city — see our city guides and confirm details with your local planning department and licensed contractors.