ADU Builder on the South Shore
An accessory dwelling unit is a second, self-contained home on your own lot. Since February 2025 Massachusetts allows one by right, and most homeowners still do not know it. ADU builders on the South Shore earn their money on the zoning, the septic and the permits, before anything is drawn.
The law changed. Most people still think they need permission.
A parent who should not be living alone. An adult child who cannot afford a first apartment on the South Shore. Meanwhile, a lot that does nothing but get mowed.
For decades the answer was the same: your town does not allow it, or you can apply for a special permit and hope the zoning board agrees. That is no longer true. Since February 2, 2025, an accessory dwelling unit is allowed by right in every Massachusetts zoning district that permits single-family homes, and any local zoning that conflicts with the state law is unenforceable.
By right means no zoning hearing and no neighbor vote. However, it does not mean no permits. There is still a building permit, still an inspection, and on most South Shore lots there is still a septic system that has an opinion about a second kitchen.
What homeowners say
ADU builders on the South Shore: three ways to build one
Which of the three fits depends on your lot, your foundation and your septic, and that is exactly what the on-site visit is for.
Inside the existing house
Converting a basement, an attic or a wing into a self-contained unit with its own entrance, kitchen and bath. Usually the cheapest of the three, because the shell already exists. So the work is egress, fire separation, insulation and a second set of services.
Attached to the house
A new structure sharing one wall with the house, with its own door. It reads as part of the home from the street and lives as a separate unit inside. Often the best answer when the basement is too low or too wet to finish.
Detached in the yard
A small standalone building, sometimes above a garage. The most private of the three and the most expensive, because it needs its own foundation, its own utility runs and its own trench from the house.
Up to 900 square feet, by right
A town cannot restrict a protected use ADU below 900 square feet. It can allow more. In other words, 900 feet is a real one-bedroom with a full kitchen, not a studio.
Septic and Title 5
On a lot with a septic system this is the item that decides the budget. A second dwelling means more design flow, and Title 5 may require upgrading or replacing the system. We find this out before you spend money on drawings, not after.
One permit set, one crew
Building permit, electrical, plumbing, and the inspections. Framing through final paint. You are not hiring us to build the box and then finding someone to finish it.
Allowed by right is not the same as free of rules.
The septic is where the budget is decidedOne company, start to finish
An ADU is a complete small house: foundation or slab, framing, roof, siding, windows, insulation, a full kitchen, a full bath, heat, and a second electrical service. On most jobs that is a general contractor coordinating six trades, and a schedule nobody owns.
You hire one. Because of that, when the inspector asks why the egress window is two inches short, there is no argument about whose job it was. It is the reason to look for ADU builders on the South Shore who build the whole unit rather than manage it.
- We check your zoning and your Title 5 status before anything is drawn
- Drawings handled, or we work from plans you already have
- Every permit pulled and every inspection managed with your town
- Your own site manager on the job, not just a phone number
- Everything itemized in writing, with a start date and a finish date
How ADU builders on the South Shore work
Free on-site visit
First we look at the lot, the house, the basement and where the septic is. That visit usually decides which of the three types makes sense.
Feasibility and estimate
Then we check your town's current rules and your Title 5 capacity. If the septic kills the project, you find out here and it has cost you nothing.
Drawings and permits
Plans your town will accept, then the building, electrical and plumbing permits. As a result of the unit being a protected use, there is no zoning hearing to wait for.
Build and walkthrough
Shell, services, finish. We walk the finished unit with you before final payment, and we are there for the final inspection.
What ADU builders on the South Shore charge
No honest ADU builder on the South Shore gives you a number over the phone, and anyone who does is guessing. What we can do is tell you what moves it.
What raises it:
- Septic. If Title 5 requires upgrading or replacing the system, this is frequently the single largest line, and it is invisible until someone checks
- Detached instead of converted. A new foundation, a new trench and a new utility run cost more than reusing a shell
- A basement that needs to be dug out. Ceiling height and egress turn a cheap conversion into an expensive one
- A full kitchen far from existing plumbing. Distance from the stack is money
- Bringing the service up to capacity, when the panel cannot carry a second dwelling
What keeps it down: converting space you already have with ceiling height that works, stacking the new kitchen and bath near existing plumbing, town sewer instead of septic, and choosing finishes before demolition rather than during.
When we are not the right call
If your lot is on septic and the system is already at capacity, the honest answer may be that an ADU does not make financial sense right now. We will tell you that at the visit instead of selling you drawings.
If you want a shed with a bed in it, that is not an ADU and it will not pass inspection. A dwelling unit needs egress, heat, a kitchen, a bath and a legal address.
We are worth it when you want the unit permitted, inspected and legal, so it still counts as a dwelling the day you sell the house.
ADU questions homeowners ask
Zoning, size and what the law allows
Do I need my town's permission to build an ADU?
Not a zoning hearing. Since February 2, 2025, a protected use accessory dwelling unit is allowed by right in every Massachusetts zoning district that permits single-family homes, and local zoning that conflicts with the state law is unenforceable. However, you still need a building permit and the trade permits, and the unit still has to pass inspection. The state publishes the rules at the Executive Office of Housing and Livable Communities.
How big can it be?
A town cannot restrict a protected use ADU below 900 square feet, and it may allow larger. The state defines a protected use ADU as no larger than half the gross floor area of the main house, or 900 square feet. In practice, 900 feet is a real one-bedroom.
Can I build one if my house is a duplex or a two-family?
Yes. A town cannot limit protected use ADUs to lots with only single-family homes on them. For example, the Attorney General's Office issued a decision on exactly this point in April 2025. Beyond the first one, your town can require a special permit.
What ADU builders on the South Shore check first
What does the septic have to do with it?
On the South Shore, often everything. A second dwelling adds design flow, and Title 5 may require upgrading or replacing the system. Towns must still comply with Title 5 when they issue the permit. In any case this is the first thing we check, because it is the item most likely to change the budget.
Will the town make me add parking?
It depends where you are. The state limits when a town can impose parking minimums on a protected use ADU, including near a bus station, which the state defines as a regular pick-up and drop-off location rather than a flag stop. We check your address against the current rules.
Are you licensed and insured?
Yes. We hold an Unrestricted Construction Supervisor License in Massachusetts, which is the license the state requires for structural work, and we carry liability and workers compensation insurance. Ask any contractor for their license and their certificate of insurance before you sign, and be careful with anyone who hesitates. Registrations can be checked with the Massachusetts Office of Consumer Affairs and Business Regulation.
Also on the South Shore: home additions, basement finishing and our finished projects.
Tell us about your lot
A free on-site visit, a check of your zoning and your septic, and a written estimate. If the lot will not take an ADU, we tell you at the visit and it has cost you nothing.