ADU Types Explained in Chatham, MA
Learn about detached, attached, and conversion ADUs in Chatham, Massachusetts. Compare costs, timelines, and which type is right for your property.
ADU Regulations in Chatham
Chatham follows the Massachusetts state baseline under the Affordable Homes Act. This means all Massachusetts state-level ADU rights apply — including by-right approval, no owner occupancy requirement, and standardized size limits. Chatham may also have additional local regulations that supplement the state baseline.
ADU Types Available in Chatham
Chatham allows 3 type(s) of ADU. Each has different cost, timeline, and design implications.
- Detached ADU — a standalone building in your yard with its own entrance, utilities, and foundation. Best for privacy and rental income.
- Attached ADU — an addition connected to your main home that shares at least one wall. Lower construction costs than detached.
- Conversion ADU — transforms existing space like a basement, attic, or garage into a separate dwelling. Fastest and cheapest to build.
Which ADU Type Is Right for You?
The best ADU type for your property in Chatham depends on your lot size, budget, and goals. If you want maximum rental income and privacy, a detached ADU is ideal. If budget is your priority, a conversion ADU reuses existing space and avoids foundation costs. An attached ADU offers a middle ground — lower cost than detached with a separate entrance. With 900 sq ft allowed, you have room for a comfortable 1-2 bedroom unit.
Learn More About ADU Rules in Chatham
For full zoning details, see our ADU zoning guide for Chatham. To understand what you'll spend, visit our ADU costs page for Chatham.
Important: State Baseline Data
The information on this page reflects Massachusetts state baseline rules. Chatham may have additional local requirements. We recommend confirming with your local building department before starting your project.
Chatham ADU Rules at a Glance
Max Size
900 sq ft
% of Home
50%
Parking
1 space(s)
Approval
BY RIGHT
Owner Occupancy
Not required
Rental Allowed
Yes
Short-Term Rental
Not allowed
Chatham Building Department
Frequently Asked Questions
What are the different types of ADUs I can build in Chatham?
Chatham allows detached, attached, conversion ADUs. Detached ADUs are standalone structures in your yard. Attached ADUs share a wall with your main home. Conversion ADUs transform existing space like a basement, attic, or garage. Each type has different costs, timelines, and design implications.
Which ADU type is cheapest to build in Chatham?
Conversion ADUs are the most affordable option in Chatham at $100-$200/sq ft, since you reuse existing structure and avoid foundation costs. See our ADU costs page for Chatham for a full breakdown.
Can I build a detached ADU in my backyard in Chatham?
Yes, detached ADUs are allowed in Chatham. Your ADU must meet setback requirements — typically a few ft from the rear property line. Check our ADU zoning page for Chatham for exact setback distances.
Can I convert my garage into an ADU in Chatham?
Yes, garage conversions are allowed in Chatham. Converting an existing garage is one of the fastest and most affordable ways to add an ADU — you're reusing the existing structure and foundation.
How accurate is the ADU data for Chatham?
The information on this page reflects Massachusetts state baseline rules under the Affordable Homes Act. Chatham may have additional local requirements that differ from the state baseline. We recommend confirming with your local building department before starting your project.
Where can I find all ADU regulations for Chatham?
Visit our complete ADU rules page for Chatham, MA for a full overview of zoning, permits, size limits, setbacks, parking, and costs. We cover all Massachusetts municipalities with data sourced from local ordinances and state law.
Check Your Address
See exactly what ADU rules apply to your specific property in Chatham.