Paying for an ADU in Massachusetts
Massachusetts now has a dedicated ADU loan program, funding to cover the planning stage, and free approved designs. Most homeowners have no idea any of it exists. Here is what is available and how the pieces fit together.
The MassHousing ADU Loan Program
In March 2026 the state launched a loan program built specifically for accessory dwelling units. It is a fixed-rate second mortgage on your existing home, available statewide through MassHousing lending partners.
The structure is what makes it worth understanding. Part of the loan is a conventional interest-bearing mortgage amortized over twenty years. That portion is matched with additional funding at zero percent interest with deferred repayment. The result is a lower effective interest rate than a straight second mortgage, and it lets a homeowner borrow more without carrying the debt service that would normally come with it.
It is construction-to-permanent financing, which means it is designed to fund the build itself rather than the planning that comes before it.
Income limits
Eligibility runs up to 135 percent of area median income, which is more generous than most people assume. Limits vary by region:
| Region | Income limit |
|---|---|
| Eastern Massachusetts | Up to $205,335 |
| Worcester County | Up to $165,345 |
| Hampden County | Up to $129,870 |
Other underwriting criteria apply. Confirm current limits and terms with a participating lender.
The timing catches people out. You cannot apply for this loan at the idea stage. Lenders expect you to have plans, permits and pre-development materials in hand and to be ready to start construction. That means the design and permitting stage has to be paid for some other way first.
That is not an oversight in the program. It is why the state also funds the planning stage separately, which is covered further down this page.
How the Pieces Fit Together
Two separate programs cover two separate stages. Used in the right order, a homeowner can get from first question to finished unit with very little out of pocket before construction financing arrives.
Feasibility Study
Find out what your property will actually support before spending real money. The state subsidizes this stage through the Massachusetts Housing Partnership.
Design & Permits
Plans drawn and local approvals secured, including Planning, Conservation and Board of Health where they apply. Predevelopment assistance may help fund this stage.
Construction Financing
With permits in hand you approach a MassHousing lending partner for the ADU loan. This is the point the program is designed for.
Build
Site work, foundation, construction and inspections through to occupancy, with the loan converting to permanent financing.
Help With the Planning Stage
The state funds several things at the front end that most homeowners never find out about.
Subsidized Feasibility Studies
The Massachusetts Housing Partnership runs an ADU Incentive Program that contributes toward a professional feasibility study. Participating providers appear in a public directory, and agree to cap what they charge the property owner.
A feasibility study looks at site conditions, access, septic or sewer capacity, utilities, zoning and setbacks, and gives a realistic sense of cost before anything is committed.
Free ADU Designs
Massachusetts ran a statewide design challenge and made the resulting ADU designs publicly available at no cost. Using one can reduce architectural expense at the design stage.
Whether a stock design suits your lot depends on access, grade and setbacks, which is a question worth answering early.
Predevelopment Assistance
Technical assistance funding exists to help homeowners get through design and permitting, which is precisely the stage the construction loan does not cover.
Availability varies, and some assistance is regional. Worth asking about before assuming you have to fund this stage yourself.
Other Ways Homeowners Pay For It
Not everyone qualifies for the state program, and not every project fits inside it. These are the routes most homeowners use.
Home Equity Line of Credit
Draw as you go and pay interest only on what you have used, which suits construction spending. Rates are usually variable, so the payment can move.
Home Equity Loan
A lump sum at a fixed rate with predictable payments. Straightforward, though you take the full amount and start paying interest on all of it immediately.
Cash-Out Refinance
Replaces your existing mortgage with a larger one. Makes sense if current rates are near or below your existing rate, and rarely otherwise.
Renovation Loans
Products that lend against the value of the property once the work is finished rather than what it is worth today. Useful when an ADU adds substantial value.
Cash or Savings
No interest and no underwriting. Worth weighing against keeping reserves for the surprises that come with any construction project.
Combining Sources
Most projects use more than one. A state loan covering the bulk, equity or savings covering the gap, is a common and sensible structure.
Be ready for a gap. Detached ADUs commonly start around $300,000, and the state loan caps at $250,000 for detached units. That difference has to come from somewhere, and it is better to plan for it at the beginning than to discover it at closing.
Conversions of existing basements and garages typically cost less than new detached construction, and are more likely to fit inside the loan limits.
What You Are Financing
A realistic budget is the starting point for any of these conversations.
Detached ADUs
900 square foot detached units start at $300,000. Site work, utility runs and septic capacity move that number more than finishes do.
Conversions
Basement and garage conversions typically cost less than new detached construction, because the structure and foundation already exist.
The Variables
Septic upgrades under Title 5, ledge, long utility runs and difficult access are the items that change a budget most. All are identifiable early.
ADU Visions is a construction company, not a lender, mortgage broker or financial advisor. The information on this page is general and provided as a starting point only. Program terms, income limits, loan amounts and availability change, and eligibility depends on your individual circumstances. Confirm all details directly with MassHousing, a participating lender, or the Massachusetts Housing Partnership before making any financial decision.
Not Sure What Your Property Supports?
Before financing matters, it helps to know what can actually be built on your lot and roughly what it will cost. That conversation is free and there is no obligation attached to it.
(508) 257-1308