What Is the MassHousing ADU Loan Program?
If you're a Massachusetts homeowner thinking about building an accessory dwelling unit, there's a new state-backed financing option worth knowing about and it's unlike anything currently available in the rest of New England.
MassHousing, Massachusetts' quasi-public state housing finance agency, launched a pilot ADU loan program in March 2025, created in response to the Affordable Homes Act signed by Governor Healey in 2024. This legislation made ADU construction a matter of right for eligible homeowners, and is predicted to add 8,000 to 10,000 new units across the state.
MassHousing’s program, funded by a $5 million opportunity fund, generated using no taxpayer dollars, is a limited-availability program offered through a network of participating local lenders. Once that funding is committed, the program closes. So if you're considering building an ADU in Massachusetts, the timing genuinely matters.
*For a snapshot of the loan program see the end of the article
Who Qualifies?
MassHousing designed this program specifically for moderate-income homeowners, not investors or landlords. To be eligible, the property must be your primary residence and a single-family home. The income limit is 135% of Area Median Income for your county, which depending on where you live in Massachusetts reaches well into six figures and covers a broad swath of homeowners who wouldn't typically qualify for subsidized programs. On the credit side, the bar is accessible: a 640 minimum score and a debt-to-income ratio up to 50%, giving more wiggle room than conventional financing typically allows.
How Much Can You Borrow?
MassHousing's program covers detached ADUs, attached ADUs, and interior conversions like finished basements or above-garage apartments. The type you build matters, because it directly determines how much you can borrow.
The program uses a two-loan structure. The first is an amortizing loan at 5.25% fixed over 20 years. The second is a deferred loan at 0% interest — and it's a match, meaning MassHousing will lend you an additional dollar-for-dollar amount on top of the amortizing loan, up to a cap. You have to take the amortizing loan before accessing the deferred portion.
Here's how the numbers break down by ADU type:
- Detached ADU: Up to $150,000 amortizing + up to $100,000 deferred = $250,000 combined maximum
- Attached or interior ADU: Up to $100,000 amortizing + up to $50,000 deferred = $150,000 combined maximum
Across both loans, the total financing cannot exceed 95% of the appraised value of your property after construction is complete. For a detached ADU borrowing the full $250,000 (half at 5.25% and half at 0%) the blended interest rate works out to roughly 3%, a figure that simply doesn't exist anywhere else in New England right now.
Key Benefits
The most obvious advantage is the rate. A blended cost of financing around 3% on a 20-year fixed loan is genuinely rare in today's market, conventional construction loans and home equity products are running well into the sixes and sevens.
Beyond the rate, MassHousing allows up to 50% of projected rental income to count toward qualifying, helpful if the ADU will generate rent but you're not collecting it yet. Combined with a 50% DTI allowance, the program is designed to stretch further than conventional financing for homeowners whose budgets are tight.
The 95% loan-to-value ceiling also means less cash out of pocket upfront. With closing costs rolled in and no requirement to bring significant equity to the table, the barrier to actually breaking ground is lower than with most comparable products.
Finally, your loan stays with MassHousing for servicing, it won't be sold off to a servicer you've never heard of. For a project this personal, that kind of continuity is worth something.
What You Need Before You Apply
This is where many homeowners get caught off guard: MassHousing's program is not designed for the early planning stages. Before a lender can lock your loan, your project must be dig ready, meaning permitted plans, contractor pricing, and all town approvals need to be in hand. If you're still sketching out ideas or getting contractor quotes, you're not there yet.
That said, you don't need to wait until you're dig ready to talk to a participating lender. In fact, starting that conversation early is encouraged, lenders can walk you through your options, help you understand what you'll qualify for, and make sure there are no surprises when you're ready to move. You just can't get to the loan lock step until everything is permitted and ready to go.
Once the loan does close, the clock starts. MassHousing requires construction to be completed within 180 days of the note date. That assumes a contractor who is lined up and ready to mobilize, not one you're still vetting. Contractor availability and scope changes can all eat into that timeline, so arriving organized is important.
What This Program Does Not Cover Well
MassHousing's ADU pilot is purpose-built for a specific borrower, and it's worth being clear about who it isn't designed for. The program is limited to single-family homes, two- and three-family properties don't qualify. It's also strictly for owner-occupants; if you're an investor or don't currently live in the property, you're not eligible.
Even for homeowners who do qualify, the loan maximums may not cover the full cost of construction. A detached ADU can easily run $250,000 or more, and in higher-cost areas of Massachusetts that number can climb further. Borrowers should go in with a realistic budget and understand they may need to bridge a gap with additional financing or cash.
Finally, this is a pilot program. The $5 million funding pool is finite, the terms are subject to change, and there's no guarantee it continues in its current form beyond this initial run. If you're eligible and serious about building, that's a reason to move sooner rather than later.
Is This Program Right for You?
MassHousing's ADU pilot is purpose-built for a specific borrower, and it's worth being clear about who it is and isn't designed for.
It's a strong fit if you:
- Own and occupy a single-family home
- Want to build an ADU for rental income or a family member
- Don't want to refinance a low first mortgage rate
- Need a lower monthly payment than conventional financing offers
- Can get your project to the dig-ready stage
It's not the right fit if you own a multifamily property or don't live in the home. The 135% AMI income cap will also exclude higher-earning households, who should explore private lender options instead. And even for eligible borrowers, the loan maximums may not cover the full cost of construction in higher-cost areas, so go in with a realistic budget.
If this sounds like you, here's how to approach the timeline:
- Start with feasibility - understand what's possible on your property before committing to anything
- Get pricing - work with a contractor to develop real numbers
- Talk to a lender early - you don't need to be dig ready to have that first conversation
- Apply when your project is ready - permits, plans, and contractor in hand
Final Takeaway
The MassHousing ADU pilot is one of the most compelling financing options available to Massachusetts homeowners right now, a blended rate around 3%, flexible qualifying terms, and high loan-to-value allowances that simply don't exist elsewhere in the region. But it's a structured program with real constraints: limited funding, income caps, single-family only, and a requirement to arrive fully prepared.
The homeowners who will benefit most are the ones who start planning early, get their projects to the dig-ready stage, and move with intention.
If you're thinking about building an ADU in Massachusetts and want to understand what's possible on your property and whether this program could work for your situation, Horizon ADU is here to help. We work with homeowners across Massachusetts from early feasibility through construction, and we can help you get your project ready to take advantage of financing opportunities like this one.
Contact Horizon ADU to get started.
