Marlborough, Massachusetts ADU builder
Accessory dwelling units built for family, rental income or both.
FJ Global designs and builds ADUs up to 900 sq ft in Marlborough and MetroWest: detached backyard units, garage conversions, basement apartments and in-law suites, from permits and framing to a finished, move-in-ready unit.
Call (517) 697-5491Massachusetts ADU law
ADUs are now allowed by right on single-family lots in Massachusetts
Since February 2025, the Massachusetts Affordable Homes Act allows one accessory dwelling unit up to 900 square feet (or half the size of the main home, whichever is smaller) by right in single-family zoning districts. No special permit, no variance and no owner-occupancy requirement for the by-right unit.
That changes the math for homeowners in Marlborough, Framingham, Sudbury, Hudson and across MetroWest: a backyard cottage, a garage apartment or a finished basement unit can house aging parents or adult children, or generate monthly rental income, on the lot you already own.
We handle the build end to end and coordinate the building permit with your town so the unit is legal, safe and code-compliant.
- Detached ADUs and backyard cottages
- Garage-to-apartment conversions and units above the garage
- Basement apartment conversions with separate entrance
- Attached in-law suites and attic apartments
- Foundation, framing, roofing, siding, windows and doors
- Kitchen, bathroom, electrical, plumbing and HVAC coordination
Which ADU fits your property?
Three ways to add a legal second unit
Garage or basement conversion. The fastest and most affordable route. The structure already exists, so the work is insulation, egress, a kitchen and bathroom, finishes and a separate entrance.
Attached addition or in-law suite. A new wing or a room above the garage with its own entrance, tied into the existing home's roofline and exterior so it looks like it was always there.
Detached ADU. A stand-alone backyard unit on its own foundation with full utilities. The most flexible option for rental income and privacy, and the one that benefits most from the by-right rule.
What you get from FJ Global
- Free on-site estimate with a written scope
- Design and layout that fits the 900 sq ft rule
- Building permit coordination with your town
- One licensed contractor from framing to finish
- Clear schedule and weekly progress updates
- Bilingual team: English and Portuguese
Recent work
Additions and second units built to belong with the home
From site work to finished exterior
The same crew that frames and finishes our home additions builds your ADU: site preparation, foundation, wood framing, enclosure and a completed exterior that matches the original house.
View Project PhotosCommon questions
ADU questions homeowners ask us
Can I build an ADU by right in Massachusetts?
Yes. One ADU up to 900 sq ft (or half the main home) is allowed by right on single-family lots statewide since February 2025. Building permits and code still apply, and some towns add dimensional rules, which we check for you.
How much does an ADU cost in Massachusetts?
A garage or basement conversion is the most affordable; a new detached unit with foundation, kitchen, bathroom and utilities costs more. We give you a written number after a free site visit.
How long does an ADU take to build?
After permits, conversions typically take a few months and detached units longer, depending on site work, utilities and finishes. You get a schedule with the estimate.
Do I need to live on the property?
The state law removed the owner-occupancy requirement for the by-right unit. We confirm the details with your town's building department as part of the permit process.
ADU service area
Serving Marlborough, MetroWest and Central Massachusetts
Related services
Thinking about an ADU on your property?
Tell us where the property is, who the unit is for and whether you are leaning toward a conversion or a detached unit. We will walk the site and give you a written estimate.
Request a Free Estimate