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ADU Design & Construction for Massachusetts Homeowners

An accessory dwelling unit is a second, self-contained home on the same lot as your house, an in-law apartment over the garage, a backyard cottage, a converted basement with its own entrance. R&D Building Solutions plans and builds ADUs as complete projects: we help you think through what your property can support, coordinate the permitting your town requires, and build a unit that works as a real home. One team, one point of contact, from the first conversation to the final walkthrough.

Request a Project ConsultationCould an ADU work for your property?

Sound familiar?

The situations this service solves

Housing a parent close by - without sharing a kitchen

Many of the ADU conversations we have start with an aging parent. An ADU keeps family next door with their own kitchen, bathroom, laundry, and front door, independence for them, peace of mind for you.

An adult child who needs a real place of their own

A finished room isn't the same as a home. A well-planned ADU gives a young adult genuine independence, separate entrance, separate utilities where practical, while staying on the family property.

Space that adapts as your life changes

The same unit can serve as a family suite this decade, a home office or studio the next, and potential rental housing where your town permits it. Building flexibility in from the start is much cheaper than adding it later.

Making better use of property you already own

An underused garage, a walk-out basement, or side-yard space may already hold most of the structure an ADU needs. We help you see what's actually feasible before you spend money on design.

Project types

The four ADU paths

Attached ADUs

An addition with its own entrance, or a converted section of the main house. Often the most practical route when the lot is tight or the family wants to stay physically connected.

Detached ADUs

A separate backyard structure built from the foundation up. The most independent option, and the one with the most site, utility, and zoning questions to answer early.

Garage conversions

Turning an existing garage, attached or detached, into living space. The shell exists; the work is in insulation, systems, egress, and making it feel like a home instead of a converted garage.

Basement ADUs

A self-contained unit within an existing basement. Ceiling height, egress, moisture control, and sound separation decide feasibility, we assess all four before anything else.

Attached ADUs →Detached ADUs →Garage Conversions →Basement ADUs →

Think it through

Planning considerations

What your lot and structures can support

Setbacks, lot coverage, septic or sewer capacity, water service, and the condition of any structure you'd convert. These determine which ADU types are realistic, and are exactly what we review on site.

Massachusetts rules and your town's bylaws

Massachusetts law now allows many ADUs by right in single-family districts, subject to size and other limits, but towns still apply their own dimensional, septic, and process requirements. We help you understand what applies to your specific property before you commit to a design.

Who will live there - now and in ten years

A unit for a parent should be planned for aging: zero-step entry, wider doorways, a bathroom that can take grab bars. A future rental needs durable finishes and clear separation. The intended use should drive the design, not the other way around.

Utilities and separation

Shared or separate heating, cooling, and electrical; laundry in the unit or shared; sound insulation between living spaces. These decisions are inexpensive on paper and expensive after drywall.

How we work

Our process for this work

  1. Feasibility conversation

    You tell us about your property and what you're hoping the ADU will do. We talk through the realistic options, including whether an ADU is the right answer at all.

  2. Site review

    We walk the property: structures, utilities, access, grading, septic/sewer. You get a grounded read on which ADU types fit your lot and roughly what each path involves.

  3. Design & scope

    Layout, entrances, systems, finishes, defined together, documented clearly, with the decisions you'll need to make laid out in order.

  4. Permitting coordination

    We coordinate the building permit and inspections with your town, and flag anything that needs zoning review before it can slow the project down.

  5. Construction

    Organized site, protected home, regular updates. You'll know what's happening each week and who to call with questions.

  6. Walkthrough & completion

    We walk the finished unit with you, complete the punch list, and hand over a home that's ready to live in.

Honest expectations

What shapes schedule and cost

No invented numbers, these are the real levers, so you can reason about your own project before we ever talk.

What can affect the schedule

  • Whether the project converts existing space or builds new structure
  • Zoning review vs. by-right permitting in your town
  • Septic system evaluation or upgrade requirements
  • Utility connections, especially for detached units
  • Design decision timing: units where selections are settled early move faster
  • Weather windows for foundation and exterior work on detached ADUs

What can affect cost

  • ADU type: converting sound existing space generally costs less than new construction
  • Site work: excavation, utility runs, and access for a detached unit
  • Kitchen and bathroom scope, the most expensive rooms per square foot
  • Septic capacity: whether the existing system can support an additional dwelling
  • Structural condition of a garage or basement being converted
  • Finish level and appliance selections
  • Accessibility features planned in from the start

Permits & inspections

ADUs in Massachusetts involve both state law and your town's bylaws. State rules now allow many ADUs by right in single-family districts, subject to size limits and local dimensional standards, but every project still requires a building permit, inspections, and often septic review. We coordinate that process with your local building department as part of the project. Every property is different: nothing on this page is legal or zoning advice, and feasibility always depends on a property-specific review.

Why R&D

How we do this differently

Feasibility honesty before design money

We'd rather tell you a detached ADU doesn't make sense on your lot than sell you drawings for one. The site review exists to protect your budget.

One team from planning through construction

No handoff between a designer who leaves and a builder who inherits. The people who plan your ADU are accountable for building it.

Communication that survives the contract

Weekly updates, real answers, and a phone that gets picked up. The middle of a build is exactly when communication matters most.

Built as a home, not a code-minimum box

Sound separation, storage, light, aging-in-place details, the things that decide whether someone actually wants to live in the unit for the next twenty years.

Questions homeowners ask

Do I need special permission to build an ADU in Massachusetts?

In many cases, Massachusetts law now allows one ADU on a single-family lot by right, meaning no special permit for the use itself, subject to size and other limits. Your town still applies its own dimensional and process requirements, and every ADU needs a building permit and inspections. The honest answer for your property depends on your lot and your town's bylaws, which is exactly what we review with you at the start.

What's the difference between an in-law apartment and an ADU?

Mostly terminology. An ADU is the formal name for a self-contained unit, its own kitchen, bathroom, and entrance, on the same lot as a primary home. "In-law apartment" usually describes the same thing built for family. The distinction that matters is legal: a permitted ADU is a recognized dwelling unit, which affects safety requirements, resale, and whether it can ever be rented.

Can I rent out an ADU?

That depends on your town. Some communities permit long-term rentals; short-term rental rules vary widely. We don't make rental-income promises, what we can do is build a unit that meets dwelling standards, so the option exists where your town allows it.

Which is cheaper: converting a garage or building a detached ADU?

Converting sound existing structure is usually the lower-cost path, because the foundation and shell already exist. But 'usually' isn't 'always', a garage with a failing slab or a basement with low ceilings can erase the savings. The site review tells you which path actually makes sense for your property.

How long does an ADU project take?

It varies too much by type and town for one honest number, a basement conversion and a from-scratch detached unit are very different projects. What we commit to is a realistic schedule before you sign anything, and clear communication when anything shifts.

Will an ADU work with my septic system?

It's one of the first questions we investigate on any unsewered property. An additional dwelling adds design flow to the system, and some systems need evaluation or upgrades to support it. Better to know that in week one than after design.

We build ADUs across Massachusetts and New Hampshire. Massachusetts and New Hampshire ADU rules differ, we'll walk you through what applies where you live.

Wondering what your property could support?

Tell us about your lot and what you're hoping an ADU could do. A real person will review it and give you a straight answer about the realistic options, no pressure, no obligation.

Request a Project ConsultationCall and speak with a real person

Tell us what you’re considering. A real person will review your request, and we will not sell or distribute your project information.

Keep exploring

Services

Attached ADUs

R&D Building Solutions plans and builds attached ADUs and in-law additions for South Shore and Middlesex County homeowners.

Services

Detached ADUs

Detached ADU construction from foundation to final walkthrough for homeowners across the South Shore and Middlesex County.

Services

Garage Conversions

We convert attached and detached garages into real living space and ADUs, serving the South Shore and Middlesex County.

Services

Basement ADUs

Basement ADUs built as complete homes, feasibility, permitting, and construction across the South Shore and Middlesex County.

Services

Basement Remodeling

Basement finishing for South Shore and Middlesex County homeowners. Every project starts with an honest moisture assessment.

Resources

Massachusetts ADU Planning Guide

How Massachusetts ADU rules work in plain English: what the state law allows by right, what your town still controls, and how to plan an accessory dwelling unit project step by step.

Resources

ADU Cost Factors

The real cost drivers behind an ADU project, unit type, site work, septic, kitchens and baths, systems, and finishes, explained honestly so you can budget with your eyes open.

Resources

ADU Permits & Project Planning

What permits an ADU actually needs in Massachusetts, who's involved at each step, and how to sequence design, septic, and building-department review so your project doesn't stall.

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