Home Equity Loan vs HELOC for Your ADU: Which Costs Less?

By Buz Artiano, BuildX | April 2026

Watch: Mastering Mortgages | David Pereira's Inside Scoop on ADU Financing

You have equity in your home and you want to build an ADU, so you went to the bank and they told you that you have two options. You can get a home equity loan or a HELOC, which sounds almost like the same thing, but they're very different. They both use your home as collateral and neither one messes with your existing mortgage, but the month to month cost and the way they're structured are very different. Picking the wrong one can cost you a lot of extra money in interest or you can get stuck making payments in amounts that you didn't plan for.

My name is Buz Artiano, and I'm the founder of BuildX. We've built dozens of ADUs across Massachusetts, mostly around the South Shore and Plymouth County. Because we handle design, permitting, and construction under one roof, we are part of all the financing conversations from day one. We know how the different types of loans play out in real life and how they work with construction. We deal with everything including septic issues, lot coverage limits, and your town's zoning requirements. All of those things affect the total project cost that these loans need to cover.

This article is going to explain exactly how a home equity loan is different from a HELOC when you're using it to build an ADU. We'll go over how each one structures their payments, where you can save money by using a certain one, and how to match the right financing to the way you want to pay it back. The goal is just to give you the information to walk into your bank knowing which type of financing is the best for your situation before they try to sell you the wrong one.

What Is the Core Difference Between a Home Equity Loan and a HELOC?

A home equity loan is kind of like a car loan. You borrow a specific amount of money, and you make the same monthly payment every month until it's paid off. The payment doesn't go down as your balance gets lower. If you borrow $250,000 and pay it down to $50,000, your monthly payment stays exactly the same until the loan is paid off.

A HELOC is an open-ended line of credit, just like a credit card. You're approved for up to a certain amount, but you only pay interest on how much you've spent. During the draw period (which is usually 10 years), you can draw money, pay the balance down, and draw again as many times as you need. Your payment adjusts every month depending on your current balance.

Neither a HELOC or home equity loan will mess with your current mortgage, they are completely separate entities. Also, neither product has a prepayment penalty, so you can pay either one off early or refinance if interest rates go down.

How Do Interest Rates Work on Each Product?

Home equity loans come with either a fixed or a variable interest rate. When the rate is fixed, your payment stays the same until the loan is paid off. People who like to strictly plan their monthly budget usually prefer a fixed interest rate because they can plan for that payment to stay the same for up to 30 years.

HELOCs always have a variable interest rate. As the market goes up or down, so do your payments. However, HELOCs will usually have interest rate caps, which means there's a limit on how high or low the interest rate can go. Your rate moves up and down within those limits, and your payments go up and down with it.

For ADU projects, the difference here really matters. If you have a HELOC balance for several years while rates are going up, your monthly payment can go up even though your balance is being paid down. With a fixed-rate home equity loan, there's no risk of the rate fluctuating, but you also don't save money if rates go down. But remember that neither of these financing options has a prepayment penalty, so you can refinance either one if interest rates go down.

Which Product Costs Less Month to Month During ADU Construction?

During the construction phase, a HELOC almost always gives you a lower monthly payment. That's because you only pay interest on the money you've already pulled. If your ADU is a $300,000 project and you've paid your builder $100,000 so far, you're only paying interest on $100,000, not the whole $300,000. That amount will go up as construction gets further to being finished, but your payment still only includes interest from the actual balance, not the full loan amount.

With a home equity loan, you get all of the money at once at closing and then you start making payments on the entire balance right away. It doesn't matter where you're at in the construction process, you're paying principal and interest on the full loan amount regardless. For someone who doesn't need all the money on day one, that's a higher monthly payment to make while construction is still in progress.

The table below shows you the main differences between the two types of financing. This is basic loan info and it's the same for whatever bank you go to, but specific terms (rates, draw periods, and qualification requirements) are different depending on which lender you use.

How Does Your Payoff Strategy Determine Which Product Wins?

The real cost difference between these two types of loans depends less on the interest rate and more on how quickly you plan to pay the money back. The timeline changes the math quite a bit depending on your family's specific situation.

Here's something we see at BuildX a lot. A daughter owns a home with lots of equity and wants to build a backyard ADU for her mom. Her mom owns her current home, so the plan is to build the ADU, move mom in, and then sell her house to pay off the construction loan. For that scenario, a HELOC is definitely the best way to go. During construction and the sale of the house, the daughter pays interest only on the amount they've paid the builder. The moment the mother's house sells, the family pays the HELOC down to zero or at least close to zero. At that point, the line of credit stays open and available, but it's not costing you anything because the balance is zero.

We call this a bridge strategy and we see it used in about one out of every three ADU projects we build. The family only needs the financing for 6 to 18 months while they sell the other house. A HELOC keeps the monthly payment low during that time because they pay interest on the balance. A home equity loan would lock them into the full monthly payment even though they're going to pay the whole thing off in a year. On a $300,000 loan, the difference in monthly payment can be hundreds of dollars. We walk everyone through all the numbers before they talk to a lender so they know which type of financing to ask for.

If there is no second property to sell and you don't plan to pay the balance for 10, 15, or 20 years, that changes things. A fixed-rate home equity loan gets rid of all the risk of your payment going up and down unpredictably. You'll know exactly what you owe every month for the entire life of the loan, and that way you can budget around that number for the next 20 years. For families on a fixed retirement income, they need the stability of a payment that never changes, they can't afford the risk of a variable rate.

How Much Can You Borrow With Each Product?

Both home equity loans and HELOCs let you borrow up to 80 percent of your home's current value, minus what you still owe on your mortgage. The math is actually super simple. If your home is worth $700,000 and you owe $250,000 on your first mortgage, the most you can borrow is $310,000 (80% of $700,000 is $560,000, minus the $250,000 you still owe). That's enough to cover a typical ADU construction project in Massachusetts.

The main difference isn't in the amount you can get, but in how you get access to the money. A home equity loan gives you the full amount of the loan at closing. A HELOC gives you access to the full amount, but only lets you pull what you need as construction moves forward. For ADU construction, where you are invoiced in phases such as foundation, framing, mechanical, and finish, the HELOC's way of doing scheduled draws fits really well with how the construction actually progresses.

What Are the Risks You Should Know About?

With a HELOC, the main risk is in the payment going up and down unpredictably. If interest rates go up during your draw period, then your monthly payment will also go up. The rate caps put a limit on how high it can go, but it can still be significantly higher than what a fixed home equity loan would have cost. If you're uncomfortable with variable payments, you definitely want to think about your risks carefully.

There's another risk that's less of a big deal, but it's good to know anyway. With a HELOC, if you pay the balance to zero and don't use it for a long time, some banks will reduce your credit limit. This is a case-by-case decision by the lender and it's actually more common when the real estate market is going down and the bank wants to reduce their risk. But it hasn't been a major issue in recent years, we just think it's worth understanding before you count on that credit line being available indefinitely.

With a home equity loan, the primary risk is overpaying. If you borrow the full construction amount and your ADU ends up costing less than you thought, or if you pay it way down with the money from selling another property, you're still stuck with the same monthly payments. You're not losing money, but you're paying more per month than necessary.

Is a Home Equity Product Always the Right Choice for ADU Financing?

No. Home equity loans and HELOCs both require you to have plenty of equity in your existing home. If you purchased your house fairly recently, if your home hasn't gone up in value enough, or if you have a large mortgage balance, you may not be able to borrow enough for an ADU project. If that's the case, renovation loans like the FHA 203K or the Fannie Mae HomeStyle Renovation Loan may be a better way to go. Those loans let you finance based on the value of the property after the ADU is built, but they require paying off your existing mortgage and wrapping everything into one loan.

We don't push families toward one way of financing over the other. The right decision depends on the equity in your home, the interest rate on your current mortgage, your cash flow, and how fast you plan on paying the money back. What we do is help you understand the total project cost so you and your bank can find the right loan for you using the real numbers.

Which Loan Fits Your ADU Project?

The choice between a home equity loan and a HELOC is not about which product is better. It is about which one matches with your current set of circumstances. If you need a stable payment and plan to pay off the loan over the long term, the home equity loan is great for that. If you plan to pay off the loan right away or want to minimize your monthly payment during construction, the HELOC gives you that ability. Both products protect your first mortgage rate, and both allow you to refinance or pay off early without penalty.