The Quick Read: A home equity line of credit sits in second position behind your existing mortgage, so it can pay for an ADU build while the first loan keeps its original terms, provided your current value leaves enough room under the lender’s combined loan-to-value cap and the build’s costs fit inside the line.
- The first mortgage stays in place. Only the new borrowing prices at today’s market.
- A standard line sizes on today’s value. The unbuilt ADU adds nothing to the number.
- On an investment property, the network ceiling is 70% CLTV, with a 700 minimum credit profile and a $500,000 maximum line.
- On a primary residence, the ceiling reaches 90% CLTV only at 720 or better credit, and only on lines up to $500,000.
- At least 75% of the line is drawn at closing, so a staged build still carries interest on most of the balance from day one.
What Does Financing an ADU With a HELOC Actually Look Like?
You keep the first mortgage and add a second lien. The first loan does not change. The new line is its own loan with its own pricing, term structure and underwriting.
How large a line the equity supports.
An equity line is sized by combined loan-to-value, occupancy, and credit — not by rental coverage. Switch the occupancy or the credit band and the ceiling moves with it.
Investment-property lines require a 700 minimum credit score; second-home lines start at a 640 minimum and primary-residence lines at 600, and the combined-LTV ceiling steps down as the credit band drops on primary-residence and second-home lines and holds on investment-property lines; the line cap steps down on primary-residence lines and holds at every tier on investment-property and second-home lines.
A debt-to-income ratio above 45% requires 680+ credit. Profiles under 640 are limited to single-family homes. At least 75% of the approved line is drawn at closing. Ceilings, floors, and caps update from Lendmire’s centralized guideline source.
Line estimate
Illustrative estimate only — not a quote, Loan Estimate, approval, or commitment to lend. The rate is an editable assumption; equity-line pricing is variable through both the draw and repayment periods and never converts to fixed. Occupancy and credit drive the ceiling together: an investment property tops out at 70% combined LTV (minimum credit 700, line cap $500,000); a second home tops out at 90% combined LTV (minimum credit 640, line cap $500,000), with the ceiling stepping down as the credit band drops (the cap holds at every tier); a primary residence tops out at 90% combined LTV (minimum credit 600), and its $750,000 maximum line is available only at 75% combined LTV or below with a 700-or-better credit profile (720 on the longer-runway program) and a full appraisal. Lines above $500,000 require a full appraisal. Credit, debt-to-income, property type, and full underwriting review all affect the final line.
That is the whole appeal. A cash-out refinance reprices the entire first-mortgage balance at current market levels. A second lien reprices only the new money. If your first mortgage is well below what lenders charge today, the second lien protects that advantage on the biggest piece of debt.
The trade has costs. The new money floats with the market. The line has a draw period and then a repayment period. And the ADU has to be funded from equity you hold today, not equity the build will create.
Lendmire is a mortgage broker (not a lender). It places these lines through select wholesale partners. The mechanics below reflect how those files behave across the network. Every figure is subject to lender guidelines and full file review.
How Is the Line Sized?
Take today’s value, multiply by the lender’s combined loan-to-value cap, then subtract the first-mortgage balance. What remains is the most the line can be, before the lender’s own line-size limit and your credit and debt ratios apply.
CLTV adds the first mortgage and the new line together and divides by value. Here is a worked example in percentages only. Say your first mortgage balance equals 40% of the home’s value, and the cap on your line is 70% CLTV. You have room for borrowing worth about 30% of value. A lower first balance leaves more room, which is why older low-balance mortgages work well for this.
Now the network’s actual caps, by occupancy:
- Investment property: 70% CLTV at 700 or better credit, lines up to $500,000, with a 700 minimum credit profile.
- Primary residence: the ceiling is 90% CLTV, and it exists only at 720 or better credit on lines up to $500,000. At 700 or better, the tiers run 75% CLTV up to $750,000 or 85% CLTV up to $500,000. At 640 and above the cap is 80% CLTV, and the program floor is 600.
- Second home: 90% CLTV is again a 720-or-better tier. The minimum credit profile is 640 and the maximum line is $500,000.
Market surveys put typical equity-line caps for ADU borrowers in a range that can sit above these ceilings. Treat those as market-wide statistics. The network figures above govern any file placed through Lendmire.
Which occupancy applies matters more than most borrowers expect. A homeowner building a backyard unit at their own house is on the primary-residence table. An investor adding a unit to a rental is on the investment table, and that table is the tightest on the network.
Why Today’s Value Is the Constraint
A standard line lends against what the property is worth now. The ADU does not exist yet, so it counts for nothing in that number.
On lines at or below $500,000, the network ordinarily uses an automated valuation with no traditional appraisal, though a higher CLTV may call for a second valuation. Every line above $500,000 requires a full appraisal, and a borrower can ask for one on any file. Lines above $500,000 are primary-residence only, need a 700 credit profile or better (720 on the 5-year draw structure), and cap at 75% CLTV.
Some specialty products lend against after-completion value. They are not widely offered, and they are not what the network’s standalone lines do. If your plan needs the finished value to make the math work, this product will not carry it.
University research points the same direction. The Terner Center at UC Berkeley found that banks have been slow to design loan products built for ADU construction. HousingWire’s summary of the follow-up work describes financing as a real obstacle for homeowners. Equity-based lines fill part of that gap. They do not fill all of it.
How the Underwriting Works, Step by Step
1. Occupancy and title. The lender first confirms which table applies. 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. That is the sharpest difference from a DSCR loan, which may accommodate an LLC subject to lender program eligibility. A rental already deeded to an LLC needs a vesting change first, or a DSCR cash-out instead.
2. Credit. The network uses a single-bureau score keyed to the primary wage earner. The report must be no more than 90 days old at closing, and there are no rescores. Credit decides your CLTV tier, so a move from one tier to the next can change the line more than the build budget does.
3. Debt-to-income. The cap is 50%, and 45% for credit profiles from 600 to 679. A ratio above 45% needs at least 680. The lender reviews your file on the interest-only payment calculated on the maximum draw, not on what you plan to draw.
4. Property. Single-family homes, 2-4 units, PUDs, townhomes and condominiums, including non-warrantable condos, are eligible. Manufactured homes, co-ops, condotels, log homes, commercial, mixed-use and agriculturally zoned properties are not offered. Modular factory-built homes are eligible only on the 5-year draw structure.
5. Valuation and lien position. The valuation test above applies. The line can sit in first or second position. For this strategy it sits second.
6. Closing and draws. At least 75% of the line is drawn at closing. Later draws carry a minimum where stated, and Texas sets a higher minimum.
That last point changes how you plan the build. The staged-draw picture, where you borrow only as invoices arrive, is how many lenders describe a HELOC for construction. On this network, most of the line is funded at closing. Size the line to the build budget, and expect to carry interest on most of it while the contractor works.
The Draw and Repayment Structures
On primary residences and second homes, two structures exist. The first has a 3-year interest-only draw followed by a 17-year fully amortizing repayment. The second has a 5-year draw followed by a 25-year repayment. Tennessee shortens both, to 3 and 12 years and 5 and 10 years.
Investment lines run the 5-year draw and 25-year repayment structure only. Pricing floats across both the draw and the repayment period and never converts to fixed. A quoted figure always carries its own structure’s terms.
The Ask CFPB explanation of a HELOC describes the general pattern. You can borrow during the draw, borrowing stops when it ends, and repayment then begins. That page warns that payments are often significantly higher once repayment starts. It also notes that some plans let you convert part of the balance to a fixed rate. That conversion option is a general-market feature. It is not part of these network lines.
The CFPB’s HELOC brochure adds a point investors miss. On a floating line, the payment can change even if you draw nothing new. Plan the ADU’s rent around that.
Where the General Rule Breaks
Thin equity. If your first mortgage already eats most of the CLTV room, a standard line cannot fund a build. A renovation or construction loan is the usual alternative, and it generally replaces the first mortgage. At that point you are no longer protecting the low first loan.
The appraisal does not always reward the build. On small properties, appraisers lean on comparable sales more than on rental income. A home with an ADU may not comp cleanly against duplexes. An improvement may support a higher appraised value, depending on comps and underwriter review. Do not underwrite your exit on the build cost coming back in value.
The ADU’s rent is not in your debt ratios yet. A unit that is not built or leased cannot be counted as income on day one. How a lender treats projected rent varies, so do not assume it offsets the line’s payment in the qualification.
Investment collateral is tighter. An investment line is capped at 70% CLTV, a 700 credit minimum and a $500,000 maximum line. There is no tier above that. A primary residence has far more room.
Exposure limits. A borrower is limited to three lines, with combined exposure capped at $2,000,000 on the higher-leverage structure and $750,000 on the other. A borrower with more than 15 financed properties is not eligible.
Geography. These lines are available only in Lendmire’s 16 full-service states: AL, CA, CO, FL, GA, IN, MI, MT, NM, NC, OH, PA, TN, TX, VA and WA. That is narrower than the 41-market DSCR footprint. New Mexico and Ohio apply a CLTV cap that depends on the credit profile. A Texas primary residence is a homestead and caps at 80% combined loan-to-value. A property listed for sale, or listed within the past 60 days, is ineligible in NC, PA, TN, TX and WA.
Credit history. A bankruptcy needs 4 years of seasoning from discharge or dismissal. Foreclosure-family history splits. One structure seasons a foreclosure at 7 years and a deed-in-lieu, pre-foreclosure or short sale at 4. The other declines that history regardless of age.
Which Funding Path Fits?
| Path | First mortgage | Borrowing basis | Best fit |
|---|---|---|---|
| Standalone HELOC | Stays in place | Current value | Low first loan, ample equity |
| Cash-out refinance | Replaced | Current value | First loan is not low |
| Renovation loan | Usually replaced | Often finished value | Thin equity |
| DSCR cash-out refinance | Replaced | Current value, rent coverage | Built, leased ADU |
The decision usually turns on two questions. First, is your first mortgage worth protecting? Second, does today’s equity cover the build? If both answers are yes, the HELOC is the clean fit. If the second answer is no, no amount of structuring on a standard line fixes it. Lendmire’s piece on how a HELOC compares with a cash-out refinance on a rental property walks through that comparison for investors.
Stress-Test Before You Close
Treat the line as a payment that floats and then steps up. Run three checks.
- Interest-only phase. Can you carry the interest on most of the line while the ADU is under construction and before it is leased? The unit earns nothing until it is finished and occupied.
- Repayment step-up. When the draw ends, the line amortizes over 17 or 25 years. The payment rises. Would the ADU’s rent and your other income still cover it?
- Overruns. The line is sized to today’s equity. If the build costs more than planned, the extra comes from cash, not from more line.
Rent coverage on an ADU is a different question from rent coverage on a DSCR loan. DSCR compares rent to PITIA only. Clearing 1.00 is not positive cash flow, because repairs, vacancy, management, utilities and capex sit outside the calculation.
Where DSCR Fits After the ADU Is Built
A DSCR cash-out refinance is a later step, not a substitute. It underwrites on property-level rental income covering the payment, subject to lender guidelines, and it replaces the first mortgage. The low first loan is gone. On most files in the network, cash-out tops out around 75% LTV on standard rentals, and about 6 months of seasoning is the common expectation.
Coverage of 1.00 is where select programs start. A separate select-lender path takes coverage below 1.00, with leverage and terms adjusted. No-ratio structures are available only through select lenders, generally for borrowers who already own a primary residence. Stronger coverage opens better pricing and leverage. Most programs want a credit score around 660, and 700 or better unlocks the strongest tiers.
If the ADU is built, leased and seasoned, rent from the unit needs documentation, such as a lease and appraisal support. The appraiser commonly relies on a rent schedule (Form 1007) or, for small income properties, an operating income statement (Form 1025). The lender then decides how the unit’s income counts.
Property type matters on the DSCR side too. DSCR financing is not offered on manufactured homes, log homes or barndominiums. For the program basics, see the complete DSCR loans guide.
Tax treatment can depend on how the funds are used and how the property is held; investors should keep clear records and speak with a qualified tax professional before relying on any deduction.
Key Terms Defined
CLTV: combined loan-to-value, which adds the first mortgage and the line together and divides by the property’s value.
Draw period: the stretch during which you can borrow from the line, usually interest-only.
Repayment period: the stretch after the draw ends, when the balance amortizes and the payment rises.
Lien position: the order in which lenders are repaid if the property is sold or foreclosed.
AVM: an automated valuation model, a computer estimate of value used in place of a traditional appraisal on smaller lines.
Frequently Asked Questions
Will a HELOC change my first mortgage?
No. The first mortgage keeps its balance, term and interest terms. The line is a separate second lien, and only the new borrowing prices at today’s market. If you later refinance the first loan and the line together, lenders generally treat that as a cash-out refinance, and the low first loan would be replaced.
Can the ADU’s future value count toward the line?
Not on a standard line. Sizing uses today’s value, so the unbuilt unit adds nothing. Some specialty products look ahead to finished value, but they are not widely offered and are not part of the network’s standalone lines.
Can I use this on a rental property?
Yes, within tighter limits. An investment-property line caps at 70% CLTV, requires at least a 700 credit profile and tops out at $500,000. The line must be held by an individual or a revocable living trust, not an LLC. Those terms are narrower than the primary-residence table.
Do I draw only as the contractor bills me?
Not entirely. At least 75% of the line is drawn at closing on the network’s lines. Later draws carry a $1,000 minimum where stated, and Texas is $4,000. Size the line to the build budget, because interest accrues on the drawn balance from the start.
When does a DSCR loan make more sense than a HELOC?
After the ADU is built, leased and seasoned, and when you want to pull equity from the property as an investor. A DSCR cash-out refinance qualifies primarily on property-level rental income covering the payment, subject to lender guidelines. It replaces the first mortgage, so the low first loan is given up in exchange.
Next Step
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.
A first mortgage worth protecting and a build the equity can actually cover are the two facts that decide this strategy. Check both before anything else.
About Lendmire
Lendmire — NMLS# 2371349 — is a mortgage broker that arranges home equity lines of credit in its 16 full-service states through wholesale lenders, on primary residences, second homes and investment properties. Every line is subject to the lender’s guidelines and full underwriting. Scotsman Guide named Lendmire a Top Mortgage Workplace in both 2025 and 2026.
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References
2. HousingWire: Financing proves an obstacle for ADUs
3. Ask CFPB: What is a home equity line of credit (HELOC)?
This article is part of Lendmire’s home equity line of credit program — full qualification details, guidelines, and scenarios live on the program page.
Related reading: Rental HELOC Calculator for a Portfolio Down Payment Strategy · Digital Rental HELOC vs Bank HELOC on a 2 to 4 Unit · Rental HELOC Fees When You Are Protecting a Low First Lien
Brandon Miller
Founder & CEO, Mortgage Loan Originator, Lendmire LLC
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Legal disclosures. Lendmire (NMLS# 2371349) is a state-licensed mortgage brokerage that arranges financing through wholesale lender relationships. Lendmire is not a direct lender, depository institution, or registered financial advisor. The discussion above is general informational content about real estate financing — it is not financial, legal, or tax advice, and readers should consult licensed professionals for guidance on their individual circumstances. Loan inquiries are subject to lender underwriting; this article does not represent a commitment to lend. Loan terms, rates, and qualification standards vary by borrower, property, and state, and are subject to change at any time. Equal Housing Opportunity. NMLS Consumer Access: nmlsconsumeraccess.org.