ADUs on the South Shore: The Complete Guide for Massachusetts Homeowners

Accessory dwelling units (ADUs) have become one of the most talked-about topics in South Shore real estate. And for good reason. An ADU can house an aging parent, provide a space for a returning adult child, generate rental income, or simply add flexible living space to your property.

Massachusetts has made significant changes to ADU law in recent years, making it easier than ever to build one. But "easier" does not mean simple. There are still zoning requirements, permitting processes, design decisions, and construction challenges to navigate.

After building ADUs and in-law suites across the South Shore, in Scituate, Hingham, Duxbury, Norwell, Cohasset, and beyond, here is everything you need to know.

An accessory dwelling unit is a secondary housing unit on a single-family residential lot. It can take several forms:

Attached ADU. Built as an addition to the main house, sharing at least one wall. Often used for in-law suites or multigenerational living.

Detached ADU. A separate structure on the same lot, such as a backyard cottage, carriage house, or garage apartment. Offers the most privacy and independence.

Interior ADU (basement or attic conversion). Converting an existing basement or attic into a self-contained living unit. Often the least expensive option, depending on the existing conditions.

Garage conversion. Converting an attached or detached garage into living space. Common on the South Shore where older homes have detached garages that are underutilized.

Each type has different cost implications, zoning considerations, and design challenges. The right choice depends on your lot, your existing home, your goals, and your budget.

In 2024, Massachusetts passed significant ADU reform as part of the Affordable Homes Act. The key changes for South Shore homeowners:

As-of-right ADUs. Municipalities can no longer prohibit ADUs outright in single-family residential zones. Homeowners have the right to build an ADU that meets the state's baseline standards without needing a special permit or variance.

Size allowance. ADUs can be up to 900 square feet or half the floor area of the principal dwelling, whichever is smaller.

No owner-occupancy requirement. The state law removed the requirement that the property owner live on-site. This opens the door to rental income even if you are not living in the main house.

Local regulations still apply. Towns can still regulate setbacks, height, design standards, and other aspects of ADU construction, but they cannot prohibit them outright. Each town on the South Shore has its own specific requirements.

This is a significant shift. A few years ago, building an ADU in many South Shore towns required a variance and a hearing before the Zoning Board of Appeals. Today, a well-designed ADU that meets the bylaw requirements can be approved administratively.

ADU costs vary significantly based on type, size, and finish level. Here are realistic ranges for the South Shore as of 2026:

Basement conversion ADU: $80,000–$150,000 This assumes the basement has adequate ceiling height (6'8" minimum per 780 CMR, the Massachusetts State Building Code; 8 feet preferred for comfort), is dry, and has reasonable access. Costs include egress windows or doors, insulation, framing, electrical, plumbing, HVAC, and finishes.

Garage conversion ADU: $100,000–$180,000 Converting a garage to living space requires insulation, new flooring, HVAC, electrical upgrades, plumbing (if adding a bathroom), and exterior modifications. The existing structure provides the shell, which reduces cost compared to building from scratch.

Attached ADU addition: $150,000–$300,000 Building a new attached ADU, typically 400 to 800 square feet, involves a new foundation, framing, roofline, exterior finishes, and full interior buildout. This is the most common type we build on the South Shore.

Detached ADU: $200,000–$400,000 A fully detached structure requires its own foundation, utilities, and complete construction from the ground up. It offers the most privacy and independence, and commands the highest rental rates.

These are full project costs including design, permits, and construction. Do not budget based on national averages; South Shore labor and material costs are higher than the national median.

Each South Shore town has its own ADU regulations. Here is a general overview, but always verify current requirements with your contractor or the local building department before committing to a design:

Scituate: ADUs allowed as-of-right in residential zones. Size limited to 900 sq ft or 50% of main dwelling. Setback requirements apply to detached structures.

Hingham: ADUs allowed as-of-right. Design standards require compatibility with the main dwelling's architecture. Detached ADUs subject to accessory structure setbacks.

Duxbury: ADUs allowed as-of-right following state law. Duxbury has historically been conservative about ADU approvals, but the state law has changed the landscape significantly.

Norwell: ADUs allowed in most residential districts. Size and design standards apply. Rental of ADUs is permitted.

Cohasset: ADUs allowed as-of-right. Cohasset's historic character overlay may apply design standards in certain areas.

Marshfield: ADUs allowed as-of-right. Marshfield has a range of residential zones with varying setback requirements.

Hull: ADUs allowed as-of-right. Hull's compact lots require careful attention to setbacks and lot coverage limits.

Hanover: ADUs allowed in residential zones. Standard setback and size requirements apply.

Pembroke: ADUs allowed as-of-right. Pembroke's larger lots generally provide more flexibility for detached ADUs.

A well-designed ADU is more than just a code-compliant box. Here is what separates a great ADU from a mediocre one:

Privacy for both households. Separate entrances, thoughtful placement of windows, and sound insulation between units are essential. The goal is for both the main house and the ADU to feel like independent homes, not like you are living on top of each other.

Full functionality in a small footprint. A 600-square-foot ADU needs to function as a complete home, with a kitchen, bathroom, sleeping area, and storage. Efficient layout design is critical. Every square foot needs to work hard.

Natural light. Small spaces feel larger with good natural light. Generous windows, skylights, and thoughtful orientation make a significant difference in how an ADU feels to live in.

Quality finishes. An ADU that will be rented or used by family members deserves quality finishes, not builder-grade materials that will need to be replaced in five years. Invest in durable flooring, solid cabinetry, and fixtures that will hold up.

Architectural compatibility. A detached ADU or addition should look like it belongs on your property. Matching siding, roofing, and window styles to the main house creates a cohesive appearance that also protects your property value.

An ADU is one of the best-returning investments a South Shore homeowner can make. Here is why:

Rental income. A well-located ADU in Scituate, Hingham, or Duxbury can generate $1,800–$2,800/month in rental income. At $2,000/month, a $200,000 ADU pays for itself in under 9 years and continues generating income indefinitely.

Property value. ADUs add significant value to South Shore properties. A detached ADU in Hingham or Scituate can add $150,000–$250,000 to your home's appraised value.

Multigenerational living. For families with aging parents or adult children, an ADU provides a solution that is both practical and financially smart. The alternative, assisted living or a separate rental, is far more expensive.

Flexibility. An ADU can serve different purposes at different stages of life. Use it for a parent today, rent it tomorrow, and use it as a home office or guest suite later.

We have built ADUs and in-law suites across the South Shore for over 30 years. Our process:

1. Free consultation. We visit your property, review your goals and budget, and give you an honest assessment of what is possible.

2. Zoning and feasibility review. Before you invest in design, we confirm what your town's zoning allows and identify any potential obstacles.

3. Design coordination. We work with architects and designers to develop plans that meet your needs, comply with local requirements, and integrate well with your existing home.

4. Permitting. We handle all permits, including building, plumbing, and electrical permits, so you do not have to navigate the process yourself.

5. Construction. Our experienced crews build your ADU with the same quality and attention to detail we bring to every project.

6. Final walkthrough. We do not consider a project complete until you are completely satisfied.

If you are thinking about an ADU in Scituate, Hingham, Duxbury, Norwell, Cohasset, Marshfield, Hull, Hanover, or Pembroke, we would love to talk. We offer free, no-obligation consultations and will give you an honest picture of what your project will involve.

Contact Valcourt Remodeling to schedule your free consultation, or call us at (617) 512-8369.