Most ADU projects are financed one of two ways: a home equity line of credit (HELOC) drawn against the equity you already have, or a construction loan underwritten against the project itself. The right choice usually comes down to two numbers — how much equity you have today, and how much the build will cost. As of June 2026, the average HELOC rate is 7.43% (Bankrate) while construction-phase rates run roughly 7.0-8.5%. But rate is only one variable. Draw mechanics, qualification, and closing costs differ far more than the headline rates do.
The Short Answer
If you have 20%+ equity and the project fits inside your borrowing limit (typically 80-85% of home value minus your mortgage balance), a HELOC is usually cheaper and simpler: minimal closing costs, you control the draws, and you pay interest only on what you have pulled. A construction or renovation loan wins when the build is large relative to your equity — these products underwrite against the completed value of the property or the full project budget, so you can borrow more than your current equity supports. Rule of thumb: HELOC for projects your existing equity covers; construction/renovation loan when it does not. Use our cost calculator to estimate your build budget first.
Side-by-Side Comparison
| HELOC | Construction / Renovation Loan | |
|---|---|---|
| Typical rate (June 2026) | 7.43% national average, variable (Bankrate, June 2026) | ~7.0-8.5% during construction, typically 0.5-1.5% above standard mortgage rates; converts to permanent financing after completion |
| Borrowing basis | Current home value: usually up to 80-85% CLTV minus existing mortgage | Completed (after-renovation) value or project budget; up to ~90% of project cost with some lenders |
| Draw mechanics | You draw funds whenever you want during a 5-10 year draw period; interest-only on the drawn balance | Lender releases funds at construction milestones (foundation, framing, rough-in, drywall, final); each draw typically requires an inspection |
| Qualification | Credit score (usually 640+), DTI, current equity; no plans required | Full project file: stamped plans, permits, signed contract with a licensed builder, detailed budget, plus standard credit/DTI review |
| Closing costs | $0-$500 at many lenders | 2-5% of loan amount, plus inspection and draw fees |
| Time to fund | 2-4 weeks | 4-8+ weeks |
| Best for | Projects your existing equity covers; garage conversions; phased builds | $200K+ builds; newer homeowners with little equity but strong income |
Rates above are national averages and ranges as of June 2026; your quote depends on credit score, CLTV, and lender. The Freddie Mac 30-year fixed averaged 6.48% the same week (June 4, 2026), which is why construction-to-permanent loans that convert to a standard mortgage can end up with a lower long-run rate than a variable HELOC.
Draw Mechanics: Who Controls the Money
This is the most underrated difference. With a HELOC, you are the bank's only checkpoint — you draw what you need, when you need it, and pay your contractor directly. That flexibility is valuable when change orders hit (and on ADU projects, they do). With a construction loan, the lender controls disbursement: funds release at fixed milestones, usually 15-25% per stage, and each release requires a site inspection. That protects you from paying ahead of work completed, but it also means delays — if an inspection takes two weeks to schedule, your contractor waits. Ask any construction lender for their draw schedule and inspection turnaround before signing.
Qualification: Current Equity vs Future Value
A HELOC is capped by today's equity. Example: $700K home, $450K mortgage balance, 85% CLTV limit = $145K of available credit ($700K × 0.85 − $450K). If your detached ADU budget is $220K, a HELOC alone cannot cover it. Construction and renovation loans solve this by underwriting against the property's value after the ADU is built. RenoFi-style renovation loans (offered through partner credit unions) lend up to 90% of the after-renovation value, up to $750K. Fannie Mae HomeStyle and FHA 203(k) renovation mortgages work similarly — the appraiser values the home as-completed, including the ADU. In high-cost markets like Los Angeles or San Diego, where a detached ADU runs $200K-$360K, this is often the only conventional path for homeowners who bought recently.
Can Future ADU Rent Help You Qualify? Mostly No
Homeowners often assume the lender will count the $1,500-$3,000/month the ADU will rent for. For HELOCs, no — HELOC underwriting uses your current income and current property value, and Fannie Mae's ADU rental income rules (updated March 2026) only apply to existing ADUs on purchase or limited cash-out refinance transactions, not to equity lines. The one verified exception on the construction side: FHA's Standard 203(k) program allows 50% of the appraiser's estimated rent for a new ADU being added to an existing structure (e.g., a garage or basement conversion) to count toward qualifying income, per FHA Mortgagee Letter 2023-17. We break down every rental-income rule, including Fannie Mae's 2026 update, in our dedicated guide.
When Each Option Wins
HELOC wins when: your equity covers the budget; the project is under ~$250K; you want to start fast (2-4 weeks vs 4-8+); you are doing a garage conversion ($80K-$180K range) or phased build; or you may not use the full amount. Construction/renovation loan wins when: the budget exceeds your available equity; the build is $200K+; you want a path to a fixed rate via construction-to-permanent conversion (one closing instead of two); or you bought recently with a low down payment. One more scenario: if your existing mortgage is at 3-4% from 2020-2021, avoid any option that refinances your first mortgage — a HELOC or standalone renovation second keeps the cheap debt in place. Compare ADU budgets across markets before you size the loan: a build that needs a construction loan in Seattle may fit a HELOC in Austin.
FAQ: HELOC vs Construction Loan
Can I use a HELOC and refinance into a mortgage later?
Yes. A common strategy: build with a HELOC, then — once the ADU is complete and adding appraised value — do a rate/term or cash-out refinance that pays off the HELOC. You take variable-rate risk during construction but avoid construction-loan paperwork. Whether it beats a construction-to-permanent loan depends on where rates sit at completion.
Do construction loans require a licensed general contractor?
Almost always. Lenders require a signed contract with a licensed, insured builder, plus plans and permits, before closing. Owner-builder construction loans exist but are rare and carry stricter terms. HELOCs have no such requirement — another reason they suit owner-managed projects.
What about a fixed-rate home equity loan instead?
A solid middle option if you know your exact budget: lump sum, fixed rate (8.12% national average for 15-year terms as of June 2026, per Bankrate), no draw flexibility. You pay interest on the full amount from day one, so it costs more than a HELOC during a staged build.
Is HELOC interest tax-deductible for an ADU build?
Interest on home equity debt used to substantially improve the home securing the loan is deductible under current law (up to the $750K total mortgage debt cap). Keep records showing the funds went into the ADU, and confirm with a tax professional.
Finance Your ADU Project
Most ADU projects are funded through HELOCs, construction loans, or cash-out refinancing. Compare rates from top lenders.
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