HELOC vs Home Equity Loan for an Accessory Dwelling Unit

The Quick Read: A HELOC fits an accessory dwelling unit build with uncertain or staged costs, while a home equity loan fits a fixed-price build, but both size the borrowing on the equity you hold today, not on the finished unit’s value or future rent. An accessory dwelling unit (ADU) is a smaller second home on your lot, such as a backyard cottage or a garage apartment. Neither product is a rental-income loan, so the rent your ADU will earn does not help you qualify.

• A HELOC works like a credit line, so you draw as the contractor bills.
• A home equity loan pays out once, which suits a firm contract price.
• Both sit behind your first mortgage and leave it untouched.
• Equity lines on rentals face tighter limits than lines on a primary home.
• After the unit is built and leased, a DSCR cash-out refinance can take over.

Side-by-Side

This table shows the structural differences. The HELOC column reflects the equity-line programs in Lendmire’s wholesale network. The home equity loan column reflects published industry norms, which vary by lender.

Two rows deserve emphasis. Both products qualify you as a borrower, not your property. And neither one gives you credit for a unit that does not exist.

Key Terms Defined

CLTV (combined loan-to-value) is your first mortgage plus the new line or loan, divided by the home’s appraised value.

Draw period is the stretch when you can borrow from a HELOC, often with interest-only payments.

Repayment period is the stretch after the draw period, when you pay down principal.

Lump sum is the full loan amount, paid out once at funding.

DSCR (debt service coverage ratio) compares a property’s monthly rent to its monthly housing obligation, meaning principal, interest, taxes, insurance and any HOA dues (PITIA).

When the HELOC Is the Better Fit

A HELOC is the better fit when your ADU budget is likely to move. Think of a conversion with unknown surprises behind the walls, or a build paid in stages for permits, foundation, framing and finishes. A line lets you borrow as bills arrive instead of paying interest on cash that sits idle.

Federal consumer guidance on HELOCs describes the structure plainly. During the draw period you can generally spend up to your limit whenever you want. Some plans allow interest-only payments in that window, then move to a repayment period.

That interest-only window helps while the unit is a construction site and earns nothing. It also carries a risk. A line that floats with the market can grow more expensive mid-build, and the payment steps up when repayment starts.

Here is a catch that surprises many borrowers. The equity-line programs in Lendmire’s network generally require at least 75% of the line to be drawn at closing. That narrows the staged-draw advantage. Across the network, two structures exist: a 3-year interest-only draw followed by 17 years of repayment, and a 5-year draw followed by 25 years. Pricing floats during both phases and never converts to fixed. Confirm how much must be drawn up front before you assume you can borrow only as contractors bill.

Picture a homeowner converting a detached garage with an open-ended scope. The contractor cannot give a firm number until walls are opened. A line gives that owner room for overruns. Whether the draw rules fit the build schedule is the question to settle with a loan officer first.

When the Home Equity Loan Is the Better Fit

A home equity loan is the better fit when the price is fixed. Per Ask CFPB’s explanation of the difference, a home equity loan is received as a lump sum and may have a fixed or adjustable structure. A HELOC lets you draw repeatedly from a maximum amount, and its payment varies with the balance.

That difference matters when a prefab unit or a firm design-build contract sets the cost in advance. You know the amount, you borrow it once, and you know your schedule from day one. There is less temptation to spend a line on extras. There is also no surprise when the index moves.

The cost of that certainty is interest on the full balance from the start. If your contractor is paid in installments across many months, you carry the whole loan before the money is spent. A lump sum also leaves no cushion for overruns.

Both products share one fact. The same source notes that if you already have a mortgage, a new home equity loan or HELOC typically is a second mortgage that you pay in addition to your first. That is good news if you hold a low legacy first mortgage, because a cash-out refinance would reprice the whole balance. It is bad news if your combined payments crowd your monthly budget.

Which Occupancy Changes Everything

Where the ADU sits matters more than which product you choose. An ADU on your own home is a primary-residence file. An ADU on a rental is an investment-property file. The network’s limits differ sharply.

On a primary residence, the network’s maximum line is $750,000. The ceiling reaches 90% CLTV only at a 720-or-better credit profile, and only for lines up to $500,000. Lower credit tiers step down from there. A line above $500,000 is primary-residence only, requires a 700 credit profile or better (720 on the 5-year-draw structure), caps at 75% CLTV, and requires a full appraisal.

On an investment property, the ceiling is 70% CLTV. The minimum credit profile is 700, the maximum line is $500,000, and only the 5-year draw, 25-year repayment structure applies. Second homes sit between the two, with a 640 floor and the same 90% ceiling at a 720 profile.

Market surveys differ from these network figures. NerdWallet’s overview of HELOCs on investment property says such lines are not offered by all lenders, carry strict qualification requirements, and typically ask for a 720 or better credit score. The network’s investment line starts at a 700 credit profile and tops out at 70% CLTV. NerdWallet also lists reserves, proof of long-term tenants, and sometimes multiple appraisals as common asks on rentals.

Several network rules apply to both occupancy types:

• Title: the borrower must hold title individually or through a revocable living trust. LLCs, corporations and partnerships cannot hold it.
• Debt load: maximum DTI is 50%, and 45% for credit profiles from 600 to 679.
• Valuation: lines at or below $500,000 ordinarily run automated valuation, and a full appraisal is required on every line above $500,000.
• Property types: manufactured homes, co-ops, condotels, log homes and agricultural or mixed-use properties are not offered.
• Availability: equity lines are offered only in the 16 states where Lendmire has full-service operations, a smaller footprint than its DSCR lending footprint. Everything is subject to lender guidelines and full file review.

Neither Product Counts the ADU You Haven’t Built

Lenders size both products on the home as it stands today. The limit is a percentage of the appraised value, minus what you still owe on the first mortgage. Nothing in that formula credits a unit that has not been permitted, built or leased.

So the equity must already be there. If your home is worth a lot and your mortgage is small, you may have room. If you bought recently with a high-leverage first mortgage, you may not. The completed ADU may support a higher appraised value later, depending on comps and underwriter review, but that does not raise today’s borrowing power.

The same logic applies to rent. The projected rent from a backyard cottage does not help you qualify for an equity line. Your personal income and debt load do the work.

Say you own a home with a modest first mortgage and want to build a detached unit. You may have enough combined equity for a line, but your debt-to-income ratio could still limit the amount. Even then, strong equity does not remove leverage caps, credit floors or property eligibility.

The Two-Step Plan: Build on Equity, Refinance on Rent

Many owners treat the equity product as a bridge. They fund construction with a personal-income product, then refinance once the unit is legal, finished and leased.

For a rental property, that second step is often a DSCR cash-out refinance. A DSCR loan is reviewed primarily on property-level rental income covering the payment, subject to lender guidelines. Across most programs in the network, cash-out refinances top out around 75% LTV, and about six months of seasoning is the common expectation. Reserves are commonly around six months of PITIA, though they vary by lender, leverage and loan size. The complete DSCR loans guide covers those mechanics in more detail.

DSCR also fixes the vesting problem. If your rental already sits in an LLC, a DSCR cash-out refinance may accommodate that title, subject to lender program eligibility. The equity lines above cannot.

Two cautions apply. First, 1.00 is where many select programs start. A separate select-lender path goes below 1.00, with leverage and terms adjusted. Clearing 1.00 does not mean positive cash flow, because repairs, vacancy, management, utilities and capital costs sit outside the calculation. Second, a second-lien payment sits outside the property-level PITIA, so you should plan your cash flow around the full obligation.

When Neither Product Fits

Sometimes the equity simply isn’t there. A large detached build or a thin equity cushion may call for construction or renovation financing, which sizes on the after-completed value and funds in stages. That route involves its own appraisal and draw schedule. Ask whether a lender will credit the finished unit before you commit.

Also consider the property type. Network equity lines accept single-family homes, 2-4 unit properties (with a 640 minimum on the 5-year-draw structure), PUDs, townhomes and condominiums, including non-warrantable ones. They do not accept manufactured homes or log homes. If you plan to add a unit to one of those property types, the equity route is closed.

The Verdict

Choose the HELOC if your costs are uncertain, your build is staged, and you can live with a floating payment. Confirm the draw rules first, because the network’s 75%-at-closing requirement narrows the flexibility. Choose the home equity loan if your contract is fixed-price and you value a steady schedule. Accept that you will pay interest on the full amount from the start.

Both are personal-credit products. Both ignore the ADU’s future value and rent. Both leave your first mortgage alone. For rentals, expect tighter limits and individual or revocable-trust title. If your rental is held in an LLC, plan for a DSCR cash-out refinance instead.

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. Every figure here is subject to lender guidelines, and this article is not a commitment to lend.

Equity is what funds the build, and rent is what pays for the next loan.

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.

References

1. CFPB: What You Should Know About Home Equity Lines of Credit

2. Ask CFPB’s explanation of the difference

3. NerdWallet’s overview of HELOCs on investment property