Everything You Need to Know About Building an ADU in Belmont, MA

Wednesday, June 4th, 2025 -As Belmont continues to evolve, so does the way we live. Whether you’re caring for aging parents, exploring rental income, or planning for multigenerational living, an Accessory Dwelling Unit (ADU) could be the right move—and now, it’s more feasible than ever in Massachusetts.

Thanks to the 2024 Affordable Homes Act, homeowners in Belmont can now build ADUs by right in most single-family zones, without needing special approval from the town. But before you hire an architect or break ground, it’s important to understand what’s allowed—and what’s not.

What Is an ADU?

An ADU is a smaller, secondary living unit on the same lot as your main home. These units can be:

• Detached (like a backyard cottage or garage conversion)

• Attached (an addition to your existing home)

• Internal (a converted attic or basement)

Potential ADU Locations

Belmont ADU Requirements at a Glance

✅ Allowed By Right
You can build one ADU per property where a single-family home is allowed or currently exists. This includes zones SR-A, B, C, D, and GR.

📏 Size Limits
The ADU must be no more than 900 square feet or 50% of your primary home’s size, whichever is smaller.

🚪 Separate Entrance Required
Your ADU must have its own private entrance.

🚗 No Parking Required (Sometimes)
If your property is within ½ mile of public transit, you’re not required to add a parking space.

🛠️ Do You Need Site Plan Review?

Most simple ADUs (within existing homes or small additions) only require a building permit. However, Design and Site Plan Review (DSPR) is needed if:

• The ADU adds a second story or exceeds the main house’s height

• Your lot coverage or open space limits are exceeded

• You’re working with a non-conforming structure

Belmont allows a 5% increase in lot coverage for ADUs, so you may have more room than you think, but it’s still wise to review zoning specifics with the Office of Planning and Building (OPB).

🌱 Energy, Safety, and Building Codes

Depending on how the ADU is built, it must comply with modern codes, such as:

• Net Zero Energy Standards for new, detached structures

• IRC/IBC Codes depending on your property type

• All plumbing, electrical, gas, and fire safety regulations

• Town of Belmont’s water and sewer connection requirements

📝 Where to Start

Before hiring a contractor or investing in architectural plans, meet with the Town’s Inspector of Buildings, Ara Yogurtian. This free consultation helps you confirm zoning, understand potential limitations, and map the best path forward.

📧 Email: ayogurtian@belmont-ma.gov
📞 Call: 617-993-2650

🤔 Not Sure If You Qualify?

You don’t have to guess. Fill out our Belmont ADU Eligibility Form to find out if your property is a candidate. It takes just two minutes and could save you thousands in planning mistakes. Plus, we’ll follow up with recommendations specific to your property.

📚 Additional Resources to Explore

Here are helpful guides, tools, and directories for planning, designing, and building your ADU:

• AARP: All About Accessory Dwelling Units

• AARP: A Step-by-Step Guide to ADU Design and Development

• AARP: The ABC’s of ADUs

• City of Boston: Planning Your Accessory Dwelling Unit

• Housing Assistance (Cape Cod): ADU Program

• Home Builders and Remodelers Association of Massachusetts

• Boston Society of Architects: ADU Architect Directory

• Lenders: Ask for referrals from neighbors, friends, or trusted professionals. Always check references and credentials.