Best HELOC Program for an Accessory Dwelling Unit

The Quick Read: The right line for an ADU depends on which property secures it, because a line on your own home, a line on a leased rental, and a DSCR cash-out refinance each solve a different part of the build. The strongest files pair a line for construction with a DSCR loan once the unit is rented. Lendmire, a mortgage broker, shops a wholesale network of HELOC lenders and matches the property, credit profile, and goal to the program that fits.

• The line is secured by the home you already own, not by the ADU you plan to build.
• A planned unit adds no rent to any coverage calculation until it exists and is leased.
• On an investment property, the network ceiling is 70% CLTV with a 700 minimum credit score. On a primary residence it reaches 90% CLTV, and only at 720 or better.
• Most lines are mostly drawn at closing, so they fit a lump-sum build better than a long phased one.
• The common exit is a DSCR cash-out refinance after the unit is built and leased.

What Does a HELOC Do for an ADU Project?

A HELOC is a revolving line secured by a home you already own. You borrow against existing equity, build the unit with the proceeds, and the line stays in place alongside or instead of your first mortgage.

The lender reviews you and the existing property. It does not underwrite the ADU. That has three practical consequences.

First, value is measured on the home as it stands today. Lines at or below $500,000 usually run on an automated valuation with no traditional appraisal, though a higher CLTV may call for a second valuation. Every line above $500,000 needs a full appraisal, and a borrower may request one at any size. Nobody credits the finished unit’s value in advance.

Second, the unit must be legal to build. Zoning, setbacks, lot coverage, and utilities can stop a project, and an equity line does not fix a permit problem. Confirm buildability before you apply.

Third, the line works as a standalone first or second lien. Keeping a low-balance first mortgage in place is the usual reason borrowers choose a second-lien line over a refinance.

CLTV means all loans against the home divided by its value. It is the number that sets how much room you have.

How Underwriting Treats an ADU Line, Step by Step

Across the wholesale network, the review follows the same order on most files.

1. Occupancy is set. An ADU on your residence is a primary-residence file. An ADU on a leased rental is an investment-property file. The ceilings differ sharply, so this is the first fork.

2. Title is checked. The line must be held by an individual borrower or a revocable living trust. LLCs, corporations, partnerships, and irrevocable, blind, or land trusts cannot hold title on these lines.

3. Credit is pulled. The program floor is 600 on primary residences, 640 on second homes, and 700 on investment properties. The score is a single-bureau model keyed to the primary wage earner.

4. Debt-to-income is tested. The maximum is 50%, and 45% for credit profiles from 600 to 679. A ratio above 45% requires at least a 680 score. The test uses the interest-only payment on the maximum draw, not just what you plan to borrow first.

5. CLTV is calculated. The existing first mortgage plus the new line must fit under the ceiling for your credit tier and occupancy.

6. Property eligibility is confirmed. Single-family homes, 2-4 unit properties, PUDs, townhomes, and condominiums (including non-warrantable) are eligible. Manufactured homes, co-ops, condotels, log homes, commercial, mixed-use, and agriculturally zoned property are not.

Notice what is missing. There is no step that credits projected ADU rent. The unit does not exist yet, so a line cannot count its income.

What Makes a Program the Best Fit?

The best program for your situation is the one whose structure matches how and when you will spend the money. These are the criteria that matter most for an ADU.

Two draw structures exist on primary residences and second homes. One runs a 3-year interest-only draw followed by a 17-year amortizing repayment. The other runs a 5-year draw followed by 25 years. Investment lines use the 5-year/25-year structure only. Pricing floats across both phases and never converts to fixed on this network.

A longer draw gives you more time to build, lease, and refinance. A shorter one can suit a borrower who plans to pay the balance down aggressively.

Which Program Fits Which Situation?

No single structure wins every scenario. Here is how the pieces typically sort out.

Run the percentages on a primary residence first. Say a home carries a first mortgage equal to 50% of its value. A borrower at 720 or better, on a line up to $500,000, can reach a 90% CLTV ceiling, leaving roughly 40% of value for the new line. At 700, the ceiling is 85%, so the room shrinks to about 35%. Lines above $500,000 are primary-residence only and cap at 75% CLTV.

Now the investment version. Picture a leased rental whose first mortgage uses 55% of value. The ceiling is 70% CLTV at any score, so the new line has about 15% of value to work with. Many ADU builds need more than that. A second-home line follows its own table, reaching 90% CLTV only at 720 or better.

Where the General Rule Breaks

The rule of thumb is simple: a line funds the build, and a DSCR loan takes it out later. Several edge cases bend it.

An LLC-held rental. The line cannot sit on an entity-titled property. The property needs a vesting change, or you skip the line and use a DSCR cash-out refinance, which can lend against an LLC-titled rental subject to program eligibility. The tradeoff is that the cash-out replaces your first lien.

A larger portfolio. Borrowers are limited to three lines, and an owner of more than 15 financed properties is not eligible. Investors with several rentals often find a DSCR cash-out pencils better than stacking lines.

An unsupported property type. Manufactured homes, log homes, and barndominiums are not offered, and neither are co-ops, condotels, and mixed-use property. An ADU project on one of these needs a different route.

Vacant land. A line can fund land, but many local jurisdictions require a primary dwelling on the parcel before an accessory unit is allowed. You may need to build the main home first, or both together.

Few banks write investor lines. Large retail lenders often decline non-owner-occupied lines or cap them tightly. That scarcity is the practical reason a broker with several wholesale options matters. The lenders that write a given file depend on occupancy, score, and property type.

A very big build. Phased construction with many small draws is a poor match, because most of the line is drawn at closing and interest runs on that balance from the start. Construction-style financing handles staged payments better.

A separate coverage path. A DSCR exit has its own rules. A 1.00 coverage ratio is where many select programs start. A separate select-lender path goes below 1.00 with leverage and terms adjusted. Neither is a promise, and both are subject to lender guidelines.

If you are weighing a rent-qualified structure, Lendmire’s explanation of how to use a DSCR HELOC for an accessory dwelling unit covers that route separately.

What Happens After the Draw Period?

Lines have two phases. Under the CFPB’s overview of home equity lines, you can borrow up to your limit during the draw period, then you lose access and enter repayment. Payments are typically variable and can change from month to month. Some lenders offer a fixed-rate conversion, but this network’s lines never convert.

That has a planning implication. During construction you carry a floating payment with no new income. When repayment starts, the payment steps up as principal amortizes. Stress-test the line against a pricing increase and a build that runs over budget before you commit. Size the line with a contingency, because a mid-build funding gap is hard to cover.

The exit is usually a DSCR cash-out refinance once the unit is built and leased. Across most of the network, cash-out refinances top out around 75% LTV on a standard rental. About six months of seasoning is the common expectation, and most programs want a score around 660, with 700 or better unlocking the strongest tiers. A DSCR loan is sized on rent divided by the full monthly obligation (principal, interest, taxes, insurance, and any HOA dues). For a finished but unleased unit, the appraiser’s market-rent opinion is used. For a leased unit, rent is generally the lesser of lease or market rent, so a lease above market adds nothing.

Clearing 1.00 is not the same as positive cash flow. The ratio leaves out repairs, vacancy, management, utilities, and capex.

The appraisal side is more involved than it looks. An academic paper on appraising properties with ADUs explains that an income approach resembles a duplex appraisal. Form 1004 is commonly used for single-unit properties, Form 1025 for 2-4 unit income property, and separate Form 1007 rent schedules are likely needed for each dwelling. Treat that paper as a source for form names and concepts, not current guidelines.

For the full picture of how the permanent loan works, see Lendmire’s complete DSCR loans guide.

Key Terms Defined

CLTV: Combined loan-to-value, meaning every loan against the home divided by its value.

Draw period: The stretch when you can borrow against the line, usually interest-only on this network.

Repayment period: The stretch after the draw ends, when you repay principal and interest on a fixed schedule.

Second lien: A loan that sits behind your existing first mortgage, so the first loan stays in place.

DSCR: Debt service coverage ratio, which compares a property’s rent to its full monthly housing obligation.

Seasoning: The ownership time a lender expects before it will refinance and pull cash out.

Vesting: How title is held, whether by an individual, a trust, or an entity.

Next Steps

If you are considering a home equity line and want to see how the numbers work, Lendmire can help you compare HELOC options based on the property, the equity available, credit profile, combined leverage, and your goals. An illustrative calculator on the site can give you a rough estimate before you apply, though it is not a quote.

Lendmire arranges these lines through select wholesale lenders in 16 full-service states, which is narrower than its 41-market DSCR footprint. Not a commitment to lend; all programs are subject to lender guidelines and full file review.

About Lendmire

Lendmire (NMLS# 2371349) is a mortgage brokerage serving homeowners and real estate investors in its 16 full-service states. Home equity lines of credit are arranged through wholesale lending channels; Lendmire brokers the line and the lender underwrites each application under its occupancy-based guidelines. Scotsman Guide named Lendmire a Top Mortgage Workplace in both 2025 and 2026.

References

1. CFPB’s overview of home equity lines

2. Appraising Properties with ADUs (Brown and Watkins)