How Much Can You Borrow on an Investment Property HELOC to Build an ADU?

The Quick Read: Usually you can borrow up to 70% of the property’s current value across all loans, minus what you already owe, with a $500,000 maximum line. The ADU’s finished value or future rent adds nothing to that math until the unit exists and is appraised, subject to lender guidelines and your credit and income review. The line is sized on what the property is worth today, not on what you plan to build.

• Leverage ceiling: 70% combined loan-to-value (CLTV) on an investment property, at a 700 credit score or higher.
• Dollar cap: lines run from $25,000 up to $500,000 on an investment property.
• Your income counts: debt-to-income (DTI) tops out at 50%, so personal income matters, not just rent.
• Title matters: the property must sit in your personal name or a revocable living trust, not an LLC.
• Draw rule: at least 75% of the line is drawn at closing, which shapes how you phase a build. Terms depend on the lender’s guidelines, the property type, the leverage, and a full review of the credit profile.

How Does the Borrowing Math Work?

The line equals today’s value times the allowed CLTV, minus every loan already on the property. Then the program’s dollar cap and your DTI can shrink it further. You get the smallest of those three numbers.

CLTV means combined loan-to-value. It stacks your first mortgage and the new line together and compares the total to the property’s value. On an investment property, the ceiling across the wholesale network Lendmire works with is 70% CLTV. Credit above 700 does not raise that ceiling. A 720 score and a 700 score both reach the same 70%, so extra credit buys you eligibility rather than extra leverage.

Here is the part that surprises people. The lender counts the full credit limit toward CLTV, not just the amount you have drawn. Sizing a line for later spending uses up your room today.

Owner-occupied homes follow a different tier. Rentals do not get it, so when you read a headline about big equity lines, check whether it describes an owner-occupied home or a rental.

What the Math Looks Like at Different Mortgage Balances

Percentages tell the story better than dollars, so treat the property’s value as 100% and subtract the loans you carry. Run the numbers on three rentals, all on an investment-property line at the 70% ceiling.

• Light mortgage: the first mortgage sits at 40% of value. That leaves 30% of value for the line, and the $500,000 cap only bites on higher-value properties.
• Middle case: the first mortgage sits at 55% of value. That leaves 15% of value, which may or may not cover your ADU budget.
• Fully leveraged: the first mortgage sits at 70% of value or more. Nothing is left, and the line is not available.

A paid-off rental gets the whole 70%, though the dollar cap may bind first. In every case the lender then checks DTI and credit before the line is final. Equity is the first test, not the only one.

Why Doesn’t the Finished ADU Count Yet?

Lenders size an investment line on the property as it stands today. The unit you have not built has no appraised value and no lease, so it has no weight in the formula. A few specialty ADU products elsewhere in the market count after-renovation value. The network’s investment-property line does not, and nothing about a plan on paper changes that.

Projected rent works the same way. A traditional equity line qualifies you personally. The lender looks at your credit, your DTI, and the payment on the line, not at what the ADU might earn later.

Agency-backed mortgage programs treat planned ADU rent differently, and the contrast is useful. Freddie Mac’s ADU fact sheet says documented ADU rent can count toward qualifying at up to 75% of the lease amount, and qualifying ADU income cannot exceed 30% of total income. Those rules belong to agency purchase and refinance programs. They do not govern a home equity line or a DSCR loan, so do not assume your line will count rent the same way.

An appraiser or lender may also decline to credit the full construction cost as value. An improvement may support a higher appraised value, depending on comps and underwriter review. Budget as though it will not.

Which Limits Bite Before Equity Does?

Credit, DTI, title, and property type each can cap you below what the equity allows. Across the network, an investment-property line has a hard 700 credit floor, and no tier sits beneath it.

DTI. The maximum is 50%, and the lender reviews your file on the interest-only payment calculated on the maximum draw. That is the full line, not the amount you plan to use. A large line can squeeze DTI even if you draw little of it. Any ratio above 45% also requires a 680 minimum score, which an investment line already clears.

Valuation. An investment line tops out at $500,000, and full appraisals are required only on lines above that. So these lines run on automated valuation and commonly close with no traditional appraisal. If you prefer one, you can still request a full appraisal.

Title. Fee simple or leasehold held by you as an individual, or by your revocable living trust. LLCs, corporations, partnerships, and irrevocable, blind, or land trusts cannot hold title. That is the sharpest structural difference from a DSCR loan, where an LLC borrower may be eligible depending on program guidelines. If your rental already sits in an LLC, you need a vesting change or a different product. Lendmire’s piece on HELOC rules for LLC-titled borrowers and how much they can borrow walks through that fork.

Property type. Single-family, two-to-four-unit, PUD, townhome, and condominium properties can be eligible, including non-warrantable condos. Manufactured homes, co-ops, condotels, log homes, commercial, mixed-use, and agricultural-zoned properties are not eligible.

Exposure. A borrower is limited to three lines. An investor who owns more than 15 financed properties is not eligible. Availability also follows Lendmire’s 16 full-service states, which is narrower than its DSCR footprint of 41 markets, including Washington, D.C.

Does a Draw Structure Fit a Phased Build?

Only partly. A home equity line is an open-end credit line you borrow against repeatedly during a draw period. After that, a repayment period begins. The Consumer Financial Protection Bureau notes that you can generally borrow up to your limit during the draw period, that repayment often runs ten or 20 years, and that some plans require a minimum initial draw.

On the network’s investment line, the structure is a 5-year interest-only draw followed by a 25-year fully amortizing repayment. At least 75% of the line is drawn at closing. Pricing floats during both the draw and the repayment period and never converts to fixed. Later draws must be at least $1,000 on most files, though Texas sets a higher minimum.

For an ADU, three things follow:

1. You pay interest on money you have not spent. If 75% of the line is drawn at closing and the foundation is months away, that cash sits idle while the interest meter runs.

2. The unit earns nothing during construction. The line payment comes out of your pocket or your other rents until a tenant moves in.

3. A floating payment can move against you. Stress-test the payment at a meaningfully higher level than today’s and confirm the portfolio still carries it before rent starts.

An honest toss-up: a smaller line sized to the build, or a bigger line that leaves cushion. The smaller line costs less interest while idle. The bigger line protects you from a cost overrun, but it uses up CLTV room and raises your DTI test, since the lender reviews your file on the full line.

What if You Just Bought the Rental?

A recently purchased rental often has too little equity for any line. DSCR purchases typically land at 75% to 80% LTV, which already sits above the 70% CLTV ceiling on an investment line. A property bought with 20% to 25% down therefore starts with little or no room.

Equity grows two ways. You pay the first mortgage down, or the property’s value rises. Until one of those happens, the line is mostly unavailable. Investors in that spot often look at a different path, such as a cash-out refinance once the loan has seasoned, a construction-style loan, or paying cash for the first phase.

Key Terms Defined

HELOC: A home equity line of credit, which lets you borrow against your property’s equity up to a limit, repay, and borrow again.

ADU: An accessory dwelling unit, a second, smaller living unit on the same lot, such as a garage conversion, backyard cottage, or basement apartment.

Draw period: The stretch when you can take money from the line, usually paying interest only.

Repayment period: The stretch after the draw period when you pay the balance down over time.

Automated valuation: A computer-generated value estimate used instead of a full appraisal, common on lines of $500,000 or less.

DSCR: Debt service coverage ratio, which divides a property’s monthly rent by its full monthly obligation (principal, interest, taxes, insurance, and any association dues).

HELOC Now, DSCR Refinance Later?

For many investors the sequence works like this: use a line to fund the build, lease the unit, and then refinance the whole property once the numbers are real. A DSCR cash-out refinance qualifies primarily on property-level rental income covering the payment, subject to lender guidelines, rather than on your personal DTI.

Cash-out on a standard rental tops out around 75% LTV across most of the network, and about 6 months of seasoning is the common expectation. Seasoning is the waiting period a lender wants between buying or refinancing and doing the next transaction. A refinance can pay off the line and replace it with a fixed structure. The spine of the network’s DSCR lineup is a 30-year fixed. The exact numbers vary by lender and program and follow a full review of property, leverage, and credit.

On coverage, 1.00 is where many select programs start, and stronger ratios open better pricing and leverage. A separate select-lender path takes coverage below 1.00, with leverage and terms adjusted. Reserves vary by lender, leverage, and loan size, and commonly run around 6 months of payments on the property.

One caution on coverage. DSCR compares rent to the monthly obligation only. Clearing 1.00 does not mean positive cash flow, because repairs, vacancy, management, utilities, and capital expenses sit outside the calculation.

A DSCR refinance has its own catch: the ADU has to be finished and generally leased or appraised before the rent can count. Agency programs document ADU rent through a comparable rent schedule form, and a lender reviewing your file may want similar support. For the full picture of how these loans work, see Lendmire’s complete DSCR loans guide.

Which Route Fits Your Situation?

• Choose the investment HELOC if you hold the rental personally or in a revocable trust, carry a low first mortgage, have a 700-plus score, and have DTI room to spare.
• Choose a DSCR cash-out refinance if the property sits in an LLC, your personal DTI is tight, or you want fixed-structure financing after the ADU is leased.
• Wait if the rental was bought recently at high leverage and has little equity.
• Use a primary-residence line only if you own the home and its own terms allow the project. Primary lines reach higher CLTV, but read the line agreement before renting out any property that secures it.

Ready to Run Your Own Numbers?

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. Call 828-256-2183 or request a quote. The site’s illustrative calculator can give you a rough starting estimate. It is not a quote.

For current guidelines and terms, see Lendmire’s investment-property HELOC programs page.

About Lendmire

As a mortgage broker (NMLS# 2371349), Lendmire helps homeowners and real estate investors in its 16 full-service states open home equity lines of credit arranged through wholesale lenders. Lendmire is never the lender; line amounts, ceilings and terms are set by the lender under its guidelines. Scotsman Guide named Lendmire a Top Mortgage Workplace in both 2025 and 2026.

References

1. Freddie Mac – ADU fact sheet

2. Consumer Financial Protection Bureau