By-Right, Backyard, and Big Business: The South Shore’s ADU Shift
PLYMOUTH - The era of the “in-law apartment” hidden in the shadows is over. With the passage of the Affordable Homes Act, Accessory Dwelling Units (ADUs) are now by-right across Massachusetts, and the South Shore is already emerging as the state’s testing ground. Plymouth might lead the Commonwealth in ADU applications, and state officials have confirmed $10 million in new incentives are on the way to help homeowners build.
The Full Story
The Old Colony Planning Council (OCPC) convened two major housing roundtables in late 2025 to dissect the new landscape, bringing together state regulators, local planners, builders, and bankers. The message was clear: The legal barriers are down, but the financial and logistical hurdles remain significant.
The “Protected Use” Revolution Claire Morehouse, ADU Coordinator for the Executive Office of Housing and Livable Communities (EOHLC), outlined the new “Protected Use” status for ADUs. Under the new law, single-family zoning districts must allow ADUs up to 900 square feet by right.
Crucially, municipalities can no longer impose “owner-occupancy” restrictions on these units. “If it meets the definition of a protected use ADU, prior conditions... like an owner occupancy restriction would be non-enforceable,” Morehouse clarified. This opens the door for property owners to rent out units without living on-site, though cities and towns retain the right to regulate short-term rentals (like Airbnbs).
Morehouse also broke news regarding state support: “We do have $5 million for ADU incentives for fiscal year 2026 as well as fiscal year 2027... that’s $10 million in total.” This funding aims to offset the steep pre-development and construction costs that often deter homeowners.
The Plymouth Surge While many towns are scrambling to update bylaws, Plymouth is already seeing a construction boom. Spencer Dancause, Plymouth’s Town Planner, revealed the town has processed 61 zoning permit applications and 44 building permit applications since August 2024.
“Plymouth has the most ADU applications within the OCPC region,” Jason Desrosier, OCPC Senior Planner, noted. In fact, early data suggests Plymouth may have the most applications in the entire state.
Dancause credited the town’s proactive approach, including a new addressing standard. To assist emergency responders, Plymouth now assigns a “U” suffix to ADU addresses (e.g., “90U Main Street”). He noted that while the state law allows for rentals, the local reality is different. “What I’ve seen the most... is a lot of aging parents who want a place for their kids to stay,” Dancause said. “The kids can't afford a single family of their own, so if the parents have a large enough property, they can construct a detached ADU.”
The Price of Privacy Despite the regulatory green light, the cost to build remains a shock to many residents. Buz Artiano of BuildX, a local design-build firm, stated that a turnkey ADU in the region typically costs between $280,000 and $390,000, driven largely by site work and septic requirements.
“The number one question people have... is what does it cost,” Artiano said. He warned that while the structures are small, they require the same expensive infrastructure—electric, water, and septic—as a full-sized home.
Financing the Backyard Build With construction costs rivaling the price of a small home, financing is critical. Representatives from Cape Cod 5 and North Easton Savings Bank detailed new lending products designed for this market.
Homeowners generally have three paths:
HELOC (Home Equity Line of Credit): The most flexible and lowest-cost option (often no closing costs), but requires existing equity.
Home Equity Loan: A fixed-rate version of the HELOC, providing stability for those on fixed incomes.
Construction Loan: A more complex product based on the “as-completed” value of the home, necessary for those who don’t have enough current equity to cover the build.
Why It Matters
For decades, the South Shore has struggled with a “missing middle” in housing—options that are neither large single-family homes nor large apartment complexes. ADUs offer a release valve for two critical demographics: seniors who want to age in place without maintaining a large property, and young adults priced out of the buying market. The rapid uptake in Plymouth proves the demand is real, but the high cost of construction means this solution currently favors existing homeowners with significant equity, rather than low-income families.
Official Minutes & Data
Key Data Points
Statewide Approvals: In the first half of 2025 alone, 550 ADUs were approved across Massachusetts, with 844 applications submitted.
Construction Cost: $280,000 - $390,000 est range for a detached ADU on the South Shore.
Incentives: $10 Million in state funds committed for FY26/FY27.
Public Comment & Q&A
Short-Term Rentals: Residents and officials clarified that while the state allows ADUs by right, towns can ban using them as short-term rentals (Airbnbs). Plymouth has maintained a prohibition on this use for certain units to prioritize long-term housing.
Septic Systems: The biggest technical barrier remains Title 5 septic capacity. Plymouth’s Health Department has released a specific flowchart to help residents navigate this.
Addresses: Plymouth’s “U” suffix system (e.g., 12U Smith St) is being eyed as a model for other towns to ensure 911 compliance.
What’s Next
State Funding: EOHLC advises residents to check mass.gov/adu for the rollout of the $10 million incentive program.
Design Challenge: The state will launch an ADU design competition to provide pre-approved, lower-cost building plans to the public.
Source Video: Old Colony Planning Council - Roundtable Part 1 | Roundtable Part 2
Once you have no longer a need for a relative to occupy the ADU can you condo the property and sell it as two separate dwellings? I know it is early in the program but I have seen conflicting legal opinions on this question.