Massachusetts ADU Regulations 2025: What Homeowners Need to Know for Multigenerational Living

For an ADU to qualify in Massachusetts, it must have:

• A separate bathroom
• A kitchen
• Bedroom(s)
• Its own entrance distinct from the main house

Think of it as a mini-home that gives family members both proximity and privacy, the perfect balance for many multigenerational arrangements.

Granny Flats are super popular in many areas of the United States and “finally” Massachusetts has caught on!

We’re a bit slow to adopt anything that might actually benefit taxpayers in this state 🙄….

Moving on, I’m super excited to share that Jim is about to start construction on a project that showcases this concept perfectly!

A family has asked him to build a main house plus a 900 sq ft ADU for the parents who have recently retired and want to compound live with their daughter and her family.

I’ll be sharing the entire process here on the blog soon! Can’t wait to show you how this space will blend togetherness with independence!

Why ADUs Are a Game-Changer for Family Living

If you’re hesitant about full-on multigenerational living where everyone shares most spaces (which can work beautifully if everyone involved has the same mindset), ADUs offer a middle ground:

• Independence with proximity: Family members maintain their own space while being close enough for support and connection
• Flexibility for changing needs: Perfect for aging parents today, adult children tomorrow, or even rental income later
• Gradual transition: Test multigenerational living without committing to a complete home renovation

For many families, this “separate but together” approach solves the biggest challenges of multigenerational arrangements.

That said, not everyone chooses this route!

Jim is currently building a multigenerational home for twin brothers and their wives. Yes, you heard that right? 😉

They decided to go with all family members under one roof but with separate “wings” for privacy.

It’s basically one big house with a central kitchen and great room with 2 “wings” off each side to accommodate each family.

It’s fascinating to see how different families approach the same concept based on their unique dynamics!

I shared a blog post about a month ago that talked about both of my experiences living in a home with a shared kitchen and our previous home with multiple kitchens.

If you missed that post, (I’ve been multi-gen living for over 14 years so I must say, I know a thing or two about it!) you can read it by clicking through to this post, “read this before you try multigenerational living.“

Here’s what you need to know if you’re considering building one:

Oh, and here’s something interesting!

While the new Mass law allows up to 900 sq ft with no restrictions, our town actually permits ADUs up to 1200 sq ft—but with certain restrictions and necessary permit.

I’ll share a dedicated blog post soon on my town’s ADU and “in-law” requirements.

This is why it’s so important to check your local regulations!

Every town interprets these guidelines a bit differently and while towns can no longer put restrictions on anything 900 sf or less, many will want something a bit larger so your town may offer that option….you just need to call your local building department to find out.

Practical Considerations

• Parking: If your property is more than half a mile from public transportation, you may need to provide one additional parking space
• Utilities: Local governments cannot require separate utility connections
• Owner occupancy: There’s no requirement that the property owner must live in either the main house or the ADU

Local Variations

While state law has streamlined the process, as I mentioned above, individual cities and towns still have their own procedures. Before starting any project, check with your local building department about:

• Application processes
• Design guidelines and square footage requirments
• Environmental or historic district requirements
• Building permit procedures
• Septic and Well requirements to tie in the ADU

ADUs vs. Integrated Multigenerational Homes: Which is Right for You?

Having lived in a fully integrated multigenerational home for 14 years, I can offer perspective on both approaches.

Remember that blog post I mentioned earlier about what you need to know before diving into multigenerational living?

After 14 years of experience, I’ve learned a lot about what works and what doesn’t—when it comes to sharing space.

There have definitely moments when I craved a little more separation and quiet.

But there have been just as many times when having everyone under one roof made for some great memories!

Our family traditions may not look like the “good old days,” but somewhere along the way, we’ve created our own—without even realizing it.

Take dinner, for example.

We’re definitely not the “sit-down-at-the-table-every-night” kind of family.

My mom cooks Sunday through Wednesday, lines everything up on the kitchen island, and hollers, “Dinner’s ready!”

Like clockwork, everyone shows up—well, except for Jim, who usually rolls in from work after 8pm and grabs his plate later. Everyone fixes their food and heads off to eat wherever they feel like. It’s not traditional, but it works for us.

Sure, the idea of gathering around the table might feel more old-school and family-focused, but in a multigenerational household, practicality often wins.

The key is to create meaningful moments in a way that fits your current lifestyle—even if it looks a little different than it did decades ago.

When an ADU Might Be Better:

• When family members strongly value their independence
• When caregiving needs are minimal
• When you’re testing multigenerational living before a bigger commitment
• When your property layout allows for a separate structure

When an Integrated Home Might Be Better:

• When caregiving needs are significant
• When you want more natural daily interaction
• When shared spaces and resources are a priority
• When your property doesn’t allow for a separate structure

I love how in our new upcoming project, the family is going with a detached ADU for the parents, while our other project with the twin brothers features connected “wings” with a separate entrance connected by a hallway/mudroom.

There are so many ways to approach compound living!

5 Critical Design Elements for Your ADU or Multigenerational Space

Whether you choose an ADU or integrated approach, certain design elements are essential.

1. Thoughtful Sound Management

Nothing threatens harmonious family living faster than unwanted noise.

Consider:

• Extra insulation in shared walls
• Solid core doors
• Strategic furniture placement
• Soft surfaces to absorb sound

2. Aging-in-Place Features

Even if not immediately needed, incorporating universal design elements saves future renovation:

• Zero-threshold entries
• Wider doorways
• Accessible bathrooms
• Good lighting

3. Clear Boundaries for Shared Resources

Establish systems for:

• Storage space allocation (this is a big one!)
• Parking arrangements
• Yard and outdoor space use
• Utility costs (if shared)

4. Privacy-Enhancing Design

Even in close quarters, everyone needs their own space:

• Strategic window placement
• Private outdoor sitting areas
• Sound-dampening landscaping between units
• Tech-free zones for quiet relaxation

5. Connection Points

Intentionally design areas where family naturally comes together:

• Shared outdoor dining space
• Connecting pathways
• Comfortable visiting areas at entry points

Are Massachusetts ADUs or Multigenerational Home Right for Your Family?

Before breaking ground, have honest conversations about:

• What level of independence each generation needs
• Financial arrangements and responsibilities (this is a big one!)
• Long-term plans and adaptability
• Communication styles and conflict resolution

Not every family is suited for close-quarters living and that’s perfectly okay! The key is honest communication about expectations before making structural commitments.