Detached vs. Attached ADUs in Massachusetts: Pros & Cons
As homeowners across Massachusetts explore ways to increase living space, boost property value, or create rental income, Accessory Dwelling Units (ADUs) have become one of the most popular options.
But one question we hear all the time:
“Should I build a detached ADU or an attached one?”
Let’s break down the pros and cons of each—specifically for homeowners here in Massachusetts, where zoning, lot size, and lifestyle goals all play a big role.
What’s the Difference?
Attached ADU: An addition that shares a wall with your main home—like a side or rear extension, a finished basement, or even an over-garage apartment.
Detached ADU: A freestanding structure, typically built in the backyard. Think of it as a “mini house” with its own foundation, utilities, and separate entrance.
Attached ADUs
Pros:
Lower construction costs
Typically cheaper to build since they share walls, rooflines, and sometimes utilities with the main home.Easier to permit
Some towns in Massachusetts have more lenient rules for additions versus detached structures.Great for multigenerational living
Keep family close while maintaining some privacy—ideal for in-laws or aging parents.
Cons:
Limited design flexibility
Must work around your existing home’s structure and style.Less privacy
Sound can carry through shared walls. Entrances may be less separate.May affect main home layout
You might need to give up existing space or reconfigure part of your house.
Detached ADUs
Pros:
Maximum privacy
Separate entrances and distance from the main home make this ideal for rental income or private guest living.Design freedom
You’re starting from scratch—choose the layout, look, and size that fits your vision.Adds long-term property value
Especially attractive to future buyers looking for rental income or flexible space.
Cons:
More expensive to build
Requires its own foundation, utility hookups, and structural components.Zoning can be trickier
Some Massachusetts towns have stricter rules for detached ADUs regarding setbacks, lot size, and placement.Takes up more yard space
Not ideal for smaller lots or homeowners who want to keep a large backyard.
Massachusetts-Specific Considerations
Zoning varies by town
While cities like Arlington, Newton, and Lexington are becoming more ADU-friendly, rules for detached vs. attached structures differ. A feasibility study is the first step to see what’s allowed on your property.Climate concerns
A detached ADU will need stronger insulation and weatherproofing. Winters here aren’t gentle!Utility tie-ins
Attached ADUs can often share main-home systems. Detached ADUs may require separate water, sewer, and electric connections—adding cost and complexity.
So… Which One Is Right for You?
Choose Attached if your budget is tighter, your lot is small, or you’re focused on family use.
Choose Detached if privacy, rental income, or future resale value are top priorities—and your property allows for it.
Let’s Help You Decide
At Mass ADU, we specialize in helping Massachusetts homeowners determine what’s possible—and what makes the most sense for their goals.
We start with a free consultation
Then offer a Feasibility Study to evaluate your lot, zoning, and ADU potential
From there, we’ll walk you through every step of the design and build process
Contact us today to see what kind of ADU is right for your property.
Call (617) 797-9167 or email leah@mass-adu.com to set up a free consultation. No pressure—just clarity, planning, and a path forward.
