The Quick Read: A home equity line of credit can fund a basement finish or an accessory dwelling unit (ADU), but the lender sizes it on what your home is worth today, not on what the finished space will be worth. The line also depends on your credit, your debt load, and how the property is titled. Here is what matters most:
- The line is sized on the home’s value before the work, so the new space does not create borrowing power for itself.
- On Lendmire’s wholesale network, the ceiling is 70% combined loan-to-value on an investment property. Primary residences and second homes reach 90% only at a 720-or-better credit profile.
- At least 75% of the line is drawn at closing, so you pay interest on most of it before a contractor bills a dollar.
- An LLC cannot hold title on these lines, which is a hard stop for many rental owners.
- Investors often plan a DSCR cash-out refinance after the unit is built and rented to pay the line off.
What Does a HELOC Actually Do for This Kind of Project?
A HELOC is a revolving credit line secured by your property. You borrow against your equity as the bills arrive, and the loan sits behind or beside your first mortgage. It works best for projects built in stages, where the cost is real but the schedule is uneven.
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.
Equity is simple: the property’s value minus what you owe on it. A lender looks at that number today. It does not look at the finished basement apartment you are about to build.
Many owners expect otherwise. The Urban Institute’s research on ADU financing notes that with a cash-out refinance, home equity loan or HELOC, the appraisal reflects the property without the ADU. The same paper finds that most ADU financing comes from savings, other liquid assets, personal loans and short-term loans. Its mortgage figures come from California only: among California ADU owners, 43% used mortgage products. Of those, 56% used a HELOC or home equity loan, 35% used a cash-out refinance, and 6% used construction or renovation financing. Those California numbers do not describe the country as a whole.
So a HELOC is common among owners who borrow against a mortgage at all. It is not the default way people build ADUs.
Key Terms Defined
Combined loan-to-value (CLTV): your first mortgage plus the new line, divided by the property’s current value.
Draw period: the stretch when you can borrow against the line and typically pay interest only.
Repayment period: the stretch after draws end, when you pay principal and interest until the balance reaches zero.
Interest-only payment: a payment that covers interest on the drawn balance and nothing toward principal.
ADU (accessory dwelling unit): a separate small home on the same lot, either detached or built into or attached to the main house.
DSCR (debt service coverage ratio): monthly rent divided by the full monthly housing payment, including principal, interest, taxes, insurance and any HOA dues.
Seasoning: the waiting period a lender wants before a refinance, usually counted from purchase or from completion of a change.
How Does a Lender Size the Line?
The lender takes a maximum CLTV, applies it to current value, and subtracts your first mortgage. Whatever remains is your maximum line, subject to dollar caps and your credit.
Market surveys report that most equity loans and HELOCs cap combined debt at about 80% of current value, per NerdWallet’s guide to ADU financing. Lendmire’s network works differently, and the ceiling depends on how you use the property. Lendmire brokers these lines through select wholesale partners, and every figure below is subject to lender guidelines and full file review.
| Occupancy | Credit floor | Top CLTV | Max line |
|---|---|---|---|
| Primary residence | 600 | 90% at 720+ | $500,000 at 90% CLTV; $750,000 at 75% CLTV, 700+ (720 on the longer-runway program) |
| Second home | 640 | 90% at 720+ | $500,000 |
| Investment property | 700 | 70% | $500,000 |
Two details sit behind that table. On a primary residence, the 90% tier applies to lines up to $500,000. A primary-residence line above $500,000 needs a credit profile of 700 or better (720 on the longer-runway program, described below) and caps at 75% CLTV. It also requires a full appraisal.
Lines at or below $500,000 ordinarily run on an automated valuation instead of a traditional appraisal, though a higher CLTV may call for a second valuation. You can also request a full appraisal. Either way, the value reflects the home as it stands today.
Run the percentages on a rental. Say your first mortgage sits at 50% of the property’s value. The investment ceiling of 70% leaves room for a line of up to 20% of value. Now take a primary residence with a 720 profile and a first mortgage at 55% of value. The 90% ceiling leaves up to 35% of value, within the $500,000 line cap. The first mortgage is what eats your headroom, so a recent purchase with a high balance often leaves very little.
Your credit and debt load matter too. The maximum debt-to-income ratio is 50%, and it drops to 45% for credit profiles between 600 and 679. Lenders review your file on the interest-only payment calculated on the maximum draw, not on what you plan to borrow first. That is stricter than many borrowers expect.
How Do Draws and Repayment Work, Step by Step?
You open the line, draw against it, pay interest during the draw period, and then switch to full repayment. The Consumer Financial Protection Bureau describes a HELOC as an open-end line you can borrow against repeatedly during the draw period, followed by a repayment period that often runs ten or 20 years.
On Lendmire’s network, equity-line files go to one of two wholesale programs. Each has its own draw structure:
- One structure is a 3-year interest-only draw followed by a 17-year fully amortizing repayment.
- The other is a 5-year interest-only draw followed by a 25-year repayment. This second one is the longer-runway program, and it is the only structure investment-property lines use.
Pricing floats through both the draw and the repayment periods and never converts to fixed. The payment can move, and it will step up when amortization begins.
The classic pitch for a HELOC is that interest accrues only on what you draw, so it suits a build that spends money in stages. That pitch weakens here. At least 75% of the line is drawn at closing on both programs. You will pay interest on most of the line from day one, whether or not a contractor has billed anything. Later draws carry a minimum, typically $1,000 where a program states one.
The practical lesson is to size the line to the project instead of borrowing the maximum. A bigger line costs money before it does any work.
Which Project Fits a HELOC Best?
A basement finish on a home with real equity fits a HELOC well. A detached ADU is the hard case, because it costs more and the property has less equity to cover it. The project type changes both the cost and what an appraiser can credit.
| Project | Permit complexity | Draw pattern | Rental potential |
|---|---|---|---|
| Basement finish | Lower | Staged, modest | Added living space |
| Basement apartment | Higher | Staged, larger | Separate unit |
| Garage conversion | Moderate | One or two stages | Separate unit possible |
| Detached ADU | Highest | Several large stages | Separate unit |
Local zoning, permits and lot rules decide whether the plan works at all, and those rules differ widely between places. Check them before you apply, because no loan fixes a project the lot cannot legally hold.
A finished, permitted space may support a higher appraised value, depending on comps and underwriter review. Unpermitted work is a different story, and appraisers and lenders may not give it credit.
HELOC, Home Equity Loan, Cash-Out Refinance or Renovation Loan?
The right tool depends on how much equity you have today and how big the build is. Each product sizes the loan differently.
| Tool | Sized on | Best when |
|---|---|---|
| HELOC | Current value | Equity exists and costs come in stages |
| Home equity loan | Current value | You know the exact cost up front |
| Cash-out refinance | Current value | Your first mortgage is worth replacing |
| Renovation loan | Value after completion | Equity is thin or the build is large |
Per NerdWallet, a HELOC or home equity loan is sized on the home’s value before the work, while a renovation or construction loan is sized on projected value after completion. That difference is the structural reason investors with little equity look at after-completion products.
A cash-out refinance resets your first mortgage, while a HELOC leaves it alone. If your existing first mortgage is better than what you could get today, a HELOC lets you keep it. If not, one cash-out loan can replace two payments.
Where the General Rule Breaks
Title and vesting. The line must be held by you as an individual or by an inter vivos revocable living trust. LLCs, corporations, partnerships, and irrevocable, blind or land trusts cannot hold title. A rental already deeded to an LLC needs a vesting change first. The alternative is a DSCR cash-out refinance, which can be made to LLC-titled borrowers, subject to program terms.
Renting the new unit. The CFPB’s HELOC brochure warns that renting out your home may be prohibited under the terms of the line. Read the agreement before you build a unit meant for tenants.
Line freezes. The same brochure notes that a lender can reduce or freeze a line if your home’s value drops. A freeze mid-build leaves you with a half-finished project. Keep cash set aside for the last stage.
Thin equity. Because the line is sized on pre-work value, a recent purchase with a high first mortgage may leave too little room. The usual workaround is a product that sizes on after-completion value.
Property type. These lines are available on single-family homes, 2-4 units, PUDs, townhomes, and condominiums, including non-warrantable ones. A 2-4 unit property needs a 640 minimum score on the longer-runway program. Modular factory-built homes are eligible on that program only. Manufactured homes, co-ops, condotels, log homes, and commercial, mixed-use or agriculturally zoned properties are not eligible on either program.
Credit events. A bankruptcy needs 4 years of seasoning from discharge or dismissal. On primary residences and second homes, one program seasons a foreclosure at 7 years and a deed-in-lieu, pre-foreclosure or short sale at 4. The other declines that history entirely, regardless of age.
Exposure limits. A borrower is limited to three lines. Combined exposure across those lines caps at $2,000,000 on the higher-leverage program and at $750,000 on the longer-runway program, so the program you choose sets the total you can carry. A borrower owning more than 15 financed properties is not eligible. Availability is limited to Lendmire’s 16 full-service states, which is narrower than its 41-market DSCR footprint, Washington, D.C. included.
What Happens After the Unit Is Built?
Many investors plan the exit before they open the line: build, rent, then refinance. A DSCR cash-out refinance can pay off the first mortgage and the line together, using the finished unit’s income. The exit loan must clear both liens, so total leverage matters from the start.
DSCR loans are designed for non-owner-occupied investment properties. They qualify primarily on property-level rental income covering the payment, subject to lender guidelines, rather than on your personal income. The complete DSCR loans guide covers the mechanics in full.
Here are the numbers that tend to shape this exit across Lendmire’s network:
- Cash-out refinances top out around 75% LTV on standard rentals. A short-term-rental exit caps cash-out at 70% on short-term-rental collateral.
- About 6 months of seasoning is the common expectation.
- Coverage of 1.00 is where many select programs start. 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 PITIA (principal, interest, taxes, insurance and HOA dues).
Clearing 1.00 does not mean positive cash flow. DSCR measures rent against the full housing payment only. Repairs, vacancy, management, utilities and capital costs sit outside it.
How an added unit’s income counts is a lender-by-lender question. It usually shows up on the appraiser’s rent schedule, Form 1007 for single-family homes or Form 1025 for 2-4 units. Short-term rental rules can vary by city, county, HOA, and property type, so investors should confirm local rules before relying on projected rental income.
What Does the Decision Look Like in Practice?
Work through it in a set order, because each step can end the plan.
1. Check the lot first. Confirm zoning, permits and any limits on the unit you want.
2. Check title. If an LLC holds the property, this product is off the table until the vesting changes.
3. Calculate headroom. Take the ceiling for your occupancy, subtract your first mortgage as a percentage of value, and compare the result to your budget.
4. Check credit and debt. Investment lines start at 700. Your debt-to-income ratio is tested on the maximum-draw payment.
5. Stress the payment. Test what your budget looks like when amortization begins and the payment steps up.
6. Plan the exit. Decide whether rent, savings or a DSCR cash-out refinance pays the line off.
A HELOC is the wrong tool when equity is thin, the build is large and detached, or the property sits in an LLC. It is also wrong when you need the line to stay open at full size no matter what the market does. In those cases, a renovation loan sized on after-completion value, or a DSCR cash-out later, is the cleaner path.
For a broader look at lines on a primary home, see Lendmire’s piece Top HELOC Providers to Build a Granny Flat or ADU.
Frequently Asked Questions
Can a HELOC cover a whole detached ADU?
Sometimes, but it depends on your equity, not on the cost of the build. The line is sized on current value minus your first mortgage, so a larger project often outruns it. On an investment property, the network ceiling is 70% CLTV with a $500,000 maximum line. Many owners of detached ADUs look at after-completion products instead.
Does the finished unit’s value count toward my line?
No. The line is sized on the property’s value before the work. The new space may support a higher appraised value later, depending on comps and underwriter review, which helps a refinance but not the original line.
Can I use my LLC to take out the line?
Not on these lines. You hold title as an individual or through a revocable living trust. If the property is already in an LLC, the options are a vesting change or a DSCR cash-out refinance.
Will I only pay interest on what I draw?
Not entirely. At least 75% of the line is drawn at closing, so interest accrues on most of it immediately. The 3-year or 5-year draw period is interest-only. After that, the payment includes principal and steps up.
How do I pay the line off once the unit is rented?
Many investors plan a DSCR cash-out refinance that pays off both the first mortgage and the line, with the new unit’s income part of the picture. Standard rentals reach about 75% LTV on cash-out, with about 6 months of seasoning as the common expectation. The lender decides how added-unit income counts. Exact terms depend on the lender’s guidelines, property type, leverage, and a full review of the borrower’s file.
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. Lendmire is a broker that arranges financing through select lenders in its wholesale network, and nothing here is a commitment to lend. You can run an illustrative estimate in the calculator, or request a quote through Lendmire’s site.
About Lendmire
Lendmire is a mortgage brokerage (NMLS# 2371349) arranging home equity lines of credit — primary-residence, second-home and investment-property lines — through a wholesale lending network in its 16 full-service states. Eligibility is determined by the lender on each file. Scotsman Guide named Lendmire a Top Mortgage Workplace in both 2025 and 2026.
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Informational only. Not a Loan Estimate, approval, or commitment to lend. Program availability and eligibility are subject to lender guidelines, credit approval, property review, and underwriting.
References
1. Urban Institute – To Increase the Housing Supply, Focus on ADU Financing
3. Consumer Financial Protection Bureau
This article is part of Lendmire’s HELOC & home equity loan program — full qualification details, guidelines, and scenarios live on the program page.
Related reading: Banks That Offer a HELOC to Pay for Home Improvements · Top HELOC Providers for Investing in Mortgage Notes · Banks That Offer a HELOC After the Death of a Spouse
Brandon Miller
Founder & CEO, Mortgage Loan Originator, Lendmire LLC
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Important disclosures. Lendmire (NMLS# 2371349) is a licensed mortgage brokerage. Lendmire is not a direct lender, depository institution, or financial advisor. All loan inquiries are subject to lender underwriting; this article does not constitute a commitment to lend. Rates, terms, and program guidelines are subject to change without notice and vary by borrower profile, property type, and state. Information in this article is general in nature and is not financial, legal, or tax advice. Equal Housing Opportunity. NMLS Consumer Access: nmlsconsumeraccess.org.