HELOC vs Construction Loan for ADUs: Which Is Right for You?

By Buz Artiano, BuildX | November 2025

When people ask us about financing their ADU, the question we get all the time is whether they should use a HELOC or a construction loan. After working with dozens of families in Massachusetts who want to build ADUs and also with great lenders who have over 30 years of experience, we know how much this decision can affect your project.

At BuildX, we build ADUs all over the state of Massachusetts. We've seen lots of families make the right financing choice and then it works out great. Unfortunately we have also seen others that struggle because they just went with the lowest rate and didn't think about oversight and protection. These financing decisions can make or break an ADU project. We will share what we have learned so you can make the right decision for you.

Why Do Most ADU Builders Choose HELOCs?

HELOCs (Home Equity Lines of Credit) are still the most popular option for ADU projects for several reasons.

Low closing costs. In most cases HELOC closing costs run less than $2,000, sometimes nothing at all. But you can pay up to $12,000 to $15,000 in closing costs for a construction loan or renovation mortgage.

Interest-only payments during construction. You only pay interest on the money you have used, just like a credit card and because BuildX can finish most ADUs in 100 to 110 days, you end up paying very little interest during that time. You are not actually borrowing the full amount on the first day. At the end of the first month, you might only be at $100,000 or $125,000, not the full amount of the project.

No prepayment penalty. Once the project is done, you can pay off the HELOC immediately without any penalties. Whether you refinance, sell property, or receive a large sum of money, you can pay down or close the line of credit any time you want.

How Do HELOC Rates Vary by Lender Type?

The amount of equity in your home decides which lenders can work with you and at what rate. Here is what we typically see in the Massachusetts market:

If you have enough equity (50% or more), a local bank is usually where you will get the best rates. If your equity is close to 20% a mortgage company will usually still lend you the money but you will pay a higher interest rate.

When Does a Construction Loan Make More Sense?

Construction loans add some protections that HELOCs don't have. If any of these apply to you, a construction loan may be the better choice:

You have less than 20% equity. A construction loan lets you borrow money against the future value of your property after the ADU is all finished. If your home is worth $600,000 and you owe $400,000, you might not have enough equity for a HELOC. A construction loan appraises the project at $800,000 or more and will give you the money that you need.

You want third-party contractor oversight. With a HELOC, no one asks questions. It's very simple and convenient, but you have to judge how your contractors are doing. With a construction loan, the bank checks the insurance, evaluates the contractor, and inspects how the project is coming along before it will let you take out more money.

You are building with a contractor you do not know well. If this is your first big construction project and you don't have people in your family who know about construction and can help you, third-party oversight protects you from contractors that might cause you problems.

What Protections Does Each Option Provide?

This table compares the oversight and protection features of HELOCs versus construction loans:

If you are not super savvy when it comes to real estate and construction contracts, you are more likely to get taken advantage of by shady contractors with a HELOC. The construction loan will give you a layer of protection that for some people can be worth the higher rate and slower funding for peace of mind.

How Do I Spot a Contractor Scam?

We must give you a critical warning here: beware of any contractor who asks for $50,000 or $100,000 upfront to get started. This is a very bad sign.

Legitimate and professional contractors only ask for payments for completed phases. Our deposits run between $20,000 and $25,000, and then you only pay for work as it's completed. After the deposit, you pay for the foundation when we are finished and you see it in place and get the documents. If a contractor needs money every two weeks or demands a large upfront payment, that is a sign that they are using your money to pay their old debts. This is when the real problems start.

Construction loans protect you from this because the bank controls when the money is withdrawn. The bank inspector checks that the work is complete before giving out any payments. With a HELOC, you have to be your own inspector.

Which Option Costs Less Over Five Years?

The lowest rate does not always mean the lowest total cost. Think about it like this.

HELOC at Prime minus 1%: This will give you lower monthly payments during construction, but there's no supervision or oversight. If your contractor screws you over or disappears, you have to take the loss.

Construction loan at Prime plus 2%: You will have a higher monthly payment, but the bank checks on the construction process and catches problems before you pay for the work.

When comparing costs, always factor in the risk of contractor issues. The extra 2% to 3% in interest basically functions as cheap insurance to cover $50,000+ problems.

Is a HELOC Right for Everyone?

Just because HELOCs are the most common way to finance an ADU does not mean that we always recommend them. The truth is, HELOCs are not right for every situation.

HELOCs work best when:

• You have 50% or more equity
• You have a contractor that you know and trust
• You have construction experience or your family or friends do
• You are ok with managing your own contractor oversight

Construction loans work best when:

• You have less than 20% equity
• This is your first major construction project
• You want the bank to manage contractors
• Your contractor is new to you or requests large upfront payments

What About a Hybrid Approach?

Many of our clients use a two-step strategy: start with a HELOC for flexibility and lower costs during construction, then they will refinance to a fixed-rate second mortgage after completion.

If you do it this way, you will have the best of both worlds. During construction, you get flexibility and low closing costs from a HELOC. Then after your ADU is finished and it appraises at a higher value, you can refinance to a fixed rate to stabilize your future payments.

The timing is what's important. Once you are 45 days from completion, put your house on the market (if you are selling) or start the process of refinancing. That way, there won't be a lot of overlap between variable HELOC rates and your fixed payment goal.

Ready to Explore Your ADU Financing Options?

The financing decision has a huge effect on the success of an ADU project so don't just blindly chase the lowest rate. Think about contractor oversight, the equity in the project you are working with, and what the total cost will be over five years.

If you are ready to explore ADU options in Massachusetts, BuildX can connect you with lending specialists who understand about ADU financing. We have worked with families in every different equity position and we can help you make the best decision for you personally.