Quick answer
A HELOC, or home equity line of credit, is an open-end line of credit secured by your home that lets you borrow repeatedly against your equity, up to a set limit, during a draw period, then repay what you borrowed over a repayment period.
Most HELOCs carry a variable interest rate, so the payment can change from month to month. Because the house is the collateral, missing payments can cost you the home.
Quick facts
- Type of credit
- Open-end (revolving), secured by the home 1
- Draw period
- Often 10 years; borrow up to the limit as needed 1
- Repayment period
- Borrowing stops; lenders often set 10 to 20 years to repay, or require the balance at once 1
- Rate
- Usually variable: an index (such as the prime rate) plus the lender’s margin 2
- Lender can
- Freeze or reduce the line if the home’s value falls or your finances worsen 2
- Position
- Usually a second lien behind the existing first mortgage
Key takeaways
- A HELOC is a credit line backed by your house. You borrow only what you need, when you need it.
- You pay interest only on the money you have drawn, not on the full limit.
- The rate usually changes over time, so your payment can go up.
- The line has two stages: a draw period, then a repayment period with bigger payments.
- The lender can freeze or cut the line if your home loses value 2.
- The limit is based on what your house is worth today, not what it will be worth with an ADU.
What a HELOC means, in plain English
Your home equity is the part of the house you own outright. It is the home’s value minus what you still owe on the mortgage.
A HELOC lets you borrow against that equity, a bit at a time. The bank sets a top limit. You take money out as bills arrive. As you pay it back, you can borrow it again during the draw period.
Because the house is the security (collateral), the lender can take the home if you stop paying. That is the main risk to keep in mind.
Why a HELOC matters for an ADU project
An ADU is not paid for in one go. You pay a designer first. Then come permit fees and utility work. The builder is paid in stages over many months.
A HELOC fits that pattern. You draw money for each bill and pay interest only on what you have used. A lump-sum loan charges interest on the full amount from day one.
The catch is size and certainty. The line may be too small for a full detached build. And a line that can be frozen is a weak base for a contract you must pay on time.
How a HELOC works
Think of a HELOC as a credit card whose limit is set by your home equity and whose security is the house itself.
The Consumer Financial Protection Bureau describes it as an “open-end” line that lets you borrow repeatedly against that equity 1.
Equity is what the home is worth minus what you still owe on it.
The line has two phases. During the draw period, often 10 years, you take money out as you need it, usually by special checks or a card, and many plans let you pay only interest on what you have drawn.
When the draw period ends, borrowing stops and the repayment period starts: lenders typically spread the balance over 10 to 20 years, and the monthly payment is often much higher than it was before 1.
Some plans instead require the full balance at once, a balloon payment the CFPB warns you must be ready to refinance or pay, or risk losing the home 2.
The rate is usually variable. It has two parts: an index, such as the U.S. prime rate or the Constant Maturity Treasury rate, and a margin the lender adds on top 2.
An introductory discount may apply for a time. HyreADU does not publish HELOC rates, because a rate is only meaningful with its date and lender; compare the index, margin, caps and fees on each offer instead.
- ApprovalThe lender appraises the home and sets a credit limit from your equity
- Draw periodBorrow as ADU bills arrive; many plans allow interest-only payments
- Draw period endsBorrowing stops; check whether the plan needs a balloon payment
- Repayment periodPrincipal plus interest, often over 10 to 20 years; payments usually rise
Lengths vary by lender; 10 years is a common draw period, not a rule. Source: [1] [2]
Worked example: how big can the line be?
Lenders size a HELOC with the combined loan-to-value ratio (CLTV): every loan secured by the home divided by its appraised value 6. All numbers below are hypothetical dollar amounts, chosen only to show the arithmetic. They are not typical values, balances or lender limits.
| Step | Hypothetical input | Result |
|---|---|---|
| Appraised home value | 800,000 (hypothetical) | — |
| First-mortgage balance | 400,000 (hypothetical) | Current LTV = 400,000 ÷ 800,000 = 50% |
| Lender’s CLTV ceiling | 80% (a hypothetical policy; each lender sets its own) | Maximum total debt = 0.80 × 800,000 = 640,000 |
| Room for a HELOC | 640,000 − 400,000 | Maximum line ≈ 240,000 |
| If the appraisal comes in at 720,000 | Same ceiling and balance | 0.80 × 720,000 − 400,000 = 176,000 |
Largest line = (V × CLTV limit) − B
V- Appraised value of the home today, in dollars
CLTV limit- The lender's combined loan-to-value ceiling, as a decimal (each lender sets its own)
B- Balance of every loan already secured by the home, in dollars
The table below runs this formula with hypothetical inputs.
Source: [6]
Two lessons. The appraisal moves the line more than anything you control, and the line is set on the house as it is today, not on the value an ADU might add. Compare the result with a realistic ADU budget from the ADU cost calculator before assuming a HELOC alone covers the build.
HELOC compared with other ways to fund an ADU
| HELOC | Home equity loan | Cash-out refinance | Construction loan | |
|---|---|---|---|---|
| How you get the money | Draw as needed up to a limit | One lump sum | New, larger first mortgage; difference paid in cash | Advances released as construction progresses |
| Rate | Usually variable | Usually fixed | Set by the new mortgage | Often interest-only during the build |
| Existing first mortgage | Stays in place | Stays in place | Replaced | Stays, or is replaced in a construction-to-permanent loan |
| Sized on | Current value | Current value | Current value | Can be based on the value after completion |
When a HELOC suits an ADU, and when it does not
What it does well
- Pay interest only on what you have drawn, which matches an ADU budget spent in stages: design and permits first, construction later.
- Keeps a low-rate first mortgage untouched, unlike a cash-out refinance.
- Can stay open as a contingency line for change orders.
Where it falls short
- A variable rate can rise during a build that takes many months.
- The lender can freeze or reduce the line if your home’s value falls 2, possibly mid-project.
- Sized on today’s value, so a large equity gap may leave it short of a full build.
- The payment can jump when the draw period ends; know the date before you start.
What to check on a HELOC offer
The CFPB’s HELOC booklet lists these items to compare across lenders 2:
- The index used and the margin added to it, and how often the rate adjusts.
- Any introductory rate and when it ends.
- Rate caps, if any, per adjustment and over the life of the line.
- Fees: application, appraisal, closing costs and any annual fee.
- Whether payments are interest-only during the draw period.
- Whether a balloon payment of the full balance is due, and whether the line can be renewed.
Where a HELOC sits in the ADU money chain
- Home value − mortgage = equity
- Lender CLTV limit → credit line
- Soft costs drawn first
- Hard costs drawn during the build
- Repayment period begins
How to get a HELOC, step by step
- Check your rough equity: a recent value estimate minus your mortgage balance.
- Get two or three offers. Compare the index, margin, caps and fees, not just the first-year rate.
- Apply. The lender checks your income, debts and credit.
- The lender orders an appraisal (a professional estimate of the home’s value). This sets the limit.
- Review the disclosures. Note when the draw period ends and how repayment works.
- Close on the line. You can now draw money by check, card or transfer.
- Draw for each ADU bill as it comes due, and keep records of every draw.
Kinds of HELOC you may be offered
| Variation | What it means | What to ask |
|---|---|---|
| Interest-only draw period | During the draw period you pay only interest on what you have used | How big will the payment be once repayment starts? |
| Principal-and-interest draw period | You repay some of the balance from the start | Does this lower my total interest cost? |
| Introductory rate | A discounted rate for an opening period 2 | When does it end, and what is the rate after? |
| Fixed-rate option | Some plans let you lock part of the balance at a fixed rate | Is there a fee to lock, and how many locks are allowed? |
| Balloon plan | The whole balance is due when the draw period ends 2 | Can I renew or refinance, and on what terms? |
Worked example: the payment jump after the draw period
All numbers are hypothetical. They are not current rates or typical balances. They only show why the payment rises. Assume a balance of 150,000 and a steady hypothetical rate of 8% a year.
| Stage | How the payment is figured | Monthly payment (rounded) |
|---|---|---|
| Draw period, interest only | 150,000 × 8% ÷ 12 | About 1,000 |
| Repayment period, 20 years | Principal and interest spread over 240 months | About 1,255 |
| Repayment period, 10 years | Principal and interest spread over 120 months | About 1,820 |
Same balance, same rate, but the payment can nearly double when the repayment period is short. If the rate also rises, the jump is bigger. Plan for the later payment, not the first one.
Where you will see HELOC terms
- The application disclosures: the CFPB booklet explains the terms lenders must show you 2.
- The appraisal report: it sets the value used for the credit limit.
- The credit agreement: draw period length, repayment rules, index, margin and caps.
- Monthly statements: your balance, the current rate and the minimum payment.
- Your builder’s payment schedule: each payment you owe becomes a draw on the line.
Rules that apply, in California and elsewhere
HELOC disclosure rules are federal. They apply in every state. The CFPB booklet describes the terms a lender must explain before you open the line 2.
California does not have a special HELOC rule for ADUs. What it does have is ADU law that shapes your budget, such as limits on fees for smaller units. See the ADU permit fees entry. Other states vary; see ADU laws by state.
This page is education, not financial or legal advice. The lender decides what you qualify for.
What a HELOC costs, and what drives it
The main cost is interest on what you draw. It depends on the index, the margin and how long you carry the balance.
Other costs can include an application fee, an appraisal fee, closing costs and an annual fee 2. Ask for every fee in writing.
For an ADU, the biggest driver is time. A long build means you carry the balance longer. Check typical build times on ADU construction time statistics before you plan interest costs.
Common mistakes with a HELOC
- Myth “My line is safe once it is open.”
- Reality The lender can freeze or reduce it if your home’s value falls or your finances change 2.
- Myth “The first payment is what I will pay.”
- Reality Interest-only payments end. The repayment payment is often much higher 1.
- Myth “The ADU will raise my limit.”
- Reality The limit is set on today’s appraised value. A finished ADU does not raise it automatically.
- Myth “The intro rate is my rate.”
- Reality An introductory rate ends. Compare the index plus margin that follows.
What to ask a HELOC lender
- What is the credit limit, and what combined loan-to-value ceiling did you use?
- Which index do you use, and what is your margin?
- Are there caps on how high the rate can go?
- How long is the draw period, and what happens when it ends?
- Is there a balloon payment?
- What fees do I pay to open, keep and close the line?
- Under what conditions can you freeze or reduce the line?
- Is there a minimum draw or a minimum balance?
Checklist: using a HELOC for your ADU
- Get a realistic budget range first, with the fee estimator for city charges.
- Compare that budget with the likely credit limit.
- Plan a cash reserve in case the line is frozen mid-build.
- Match draws to your builder’s payment schedule.
- Write down the date the draw period ends.
- Work out the repayment payment before you sign the build contract.
- Keep receipts for every draw, for your records and your tax adviser.
Compare your options
- Financing comparison toolStaged money versus available money, side by side
- ADU financing landscapeWhat lenders and appraisers actually do with ADUs
- ADU financing statisticsSourced figures only
- ADU financing hubEvery financing guide in one place
Questions about heloc
Can I use a HELOC to build an ADU?
Yes, if your equity and the lender’s combined loan-to-value limit leave enough room. The money is yours to spend on design, permits and construction. The constraint is size: the line is based on the home’s current value, so it may not cover a full detached build without savings or another loan.
What is the difference between a HELOC and a home equity loan?
A HELOC is a revolving line you draw from as needed, usually at a variable rate. A home equity loan pays one lump sum, usually at a fixed rate, with regular payments from the start. Both are secured by your home.
What happens when the HELOC draw period ends?
You can no longer borrow, and you start repaying principal as well as interest, often over 10 to 20 years, so the payment usually rises. Some plans require the whole balance at once as a balloon payment.
Can a lender freeze my HELOC during construction?
Yes. HELOCs generally let the lender freeze or reduce the line if your home’s value falls or your finances worsen, according to the CFPB. Keep a reserve so a frozen line does not stop the build.
Is HELOC interest tax deductible for an ADU?
That depends on federal and state tax rules and your situation, and this page does not cover tax treatment. Ask a tax professional before relying on a deduction.
How much can I borrow with a HELOC?
It depends on your home’s appraised value, what you owe, your income and the lender’s combined loan-to-value limit. Each lender sets its own limit. Take the value, multiply by the limit, and subtract your mortgage. The worked example above shows the steps with hypothetical numbers.
Is a HELOC a good idea for an ADU?
It can be, if you have enough equity and can handle a payment that may rise. It suits a build paid in stages. It is a weaker fit if the line would be too small, or if a freeze mid-build would leave you unable to pay your builder.
What are the downsides of a HELOC?
The rate usually changes, so payments can rise. The payment often jumps when repayment starts. The lender can freeze the line. And your home is the collateral, so missing payments can lead to losing it.
Does a HELOC require an appraisal?
Lenders usually need a value for the home to set the limit. That may be a full appraisal or another valuation method, depending on the lender. Ask which one they use and who pays for it.
Can I pay off a HELOC early?
Often yes, but some plans charge a fee if you close the line early. Ask about early closure fees before you sign, and read the credit agreement.
Sources
- Consumer Financial Protection Bureau, What is a home equity line of credit (HELOC)?, retrieved .
- Consumer Financial Protection Bureau, What you should know about home equity lines of credit (booklet), retrieved .
- Consumer Financial Protection Bureau, What is a home equity loan?, retrieved .
- Consumer Financial Protection Bureau, What other types of loans are similar to a HELOC?, retrieved .
- Consumer Financial Protection Bureau, What is a construction loan?, retrieved .
- Consumer Financial Protection Bureau, What is a loan-to-value ratio?, retrieved .
Expert review
Written by the HyreADU Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Definitions and loan features taken from CFPB pages and the CFPB HELOC booklet, read on 7 October 2026. The worked example uses labelled hypothetical numbers for arithmetic only. No interest rates are quoted. Education, not financial advice.
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