What 1,224 ADU Permits Taught Me About Massachusetts Housing

One year ago, Massachusetts passed one of the strongest ADU laws in the country. Accessory dwelling units—granny flats, in-law apartments, backyard cottages—can now be built by right in single-family zones statewide.

I've spent the past few months tracking what's actually happening on the ground. Not press releases. Not projections. Real permit data, scraped directly from town portals and cross-referenced with state survey data.

Here's what I found.

The headline number is good

1,224 ADUs approved across 221 towns in year one.

That's a 75% approval rate on 1,639 applications. For context, Massachusetts is outpacing California's per-capita rate from their first year of ADU reform by 1.27x.

The law is working. But not evenly.

The state just confirmed the numbers

On February 4th, Massachusetts launched its own ADU tracker, citing the same 1,224 approved ADUs. It's built on the same EOHLC survey data that powers this site — which means the numbers you've been reading here are the same numbers the Governor's office is using.

The state tracker is a good step. But if you've tried to use it, you've probably noticed the gaps: no searchable table, no town-level approval rates, no per-capita normalization, and a map with some display quirks. That's part of why ADU Pulse exists — to turn the raw data into something you can actually use.

For a deeper look at how the state's tracker compares to national data and where Massachusetts ranks nationally, see our full national comparison.

Some towns rubber-stamp. Others stall.

100% approval rate: Nantucket (27), Lowell (26), Fairhaven (18), Harwich (15)

Under 25% approval rate: Gardner (0%), Barnstable (19%), Danvers (22%)

Barnstable is the outlier that should concern policymakers. They received 31 applications—real demand—but only approved 6. That's not a lack of interest. That's friction.

Meanwhile, Gardner has approved zero out of seven applications. The law says ADUs are allowed by right. Someone should ask Gardner what's happening.

Lowell may be the most interesting story in the data. A significant share of its 26 permits came from the Belvidere neighborhood — the same area where residents vocally opposed the city's ADU ordinance in 2023. Two years later, those same neighborhoods are among the most active ADU builders in the state. When the economics work, initial skepticism often gives way to practical engagement.

Urban and suburban ADUs look completely different

In dense cities, ADUs mean basement conversions:

• Revere: 100% attached
• Boston: 84% attached
• Milton: 96% attached

In suburban and Cape towns, ADUs mean backyard cottages:

• Harwich: 100% detached
• Nantucket: 89% detached
• Edgartown: 100% detached

This matters for cost estimates. A basement conversion might run $50K. A detached new build can exceed $500K. Same law, completely different projects.

The Revere story no one's talking about

When I scraped Revere's permit portal, I found 33 ADU permits—nearly double what the state survey reported (17).

But here's the interesting part: at least 4 of those permits explicitly mention "legalizing work done without permits" or "correcting violations."

Revere's ADU wave isn't just new construction. It's a legalization wave. Homeowners who built unpermitted units years ago are now coming into compliance.

This is the law working exactly as intended—bringing shadow housing into the light.

Cost variance is massive

Looking at Lexington permits with cost data:

• Low end: ~$4/sq ft (minimal basement work)
• High end: ~$635/sq ft (full detached new construction)

That's not a typo. The range is 150x. Homeowners planning budgets based on "average ADU cost" articles are in for a surprise. The type of ADU—not the town—is the biggest cost driver.

Wealthy suburbs tell different stories

Both Lexington and Newton are affluent suburbs with strong ADU demand.

• Lexington: 6 submitted, 6 approved (100%)
• Newton: 40 submitted, 18 approved (45%)

Same demographics. Same housing pressure. Very different outcomes. Newton's approval rate suggests something in their process is creating friction that Lexington has avoided.

What I'm still trying to figure out

The data shows what is happening. It doesn't always show why.

• Why is Barnstable at 19% approval when neighboring Cape towns are much higher?
• What's causing Newton's backlog?
• Which builders are doing the most ADU work, and where?
• How long does it actually take from application to approval?

I'm adding more towns every week. If you're a homeowner, builder, policymaker, or just curious about housing in Massachusetts, I'd love to hear what data would be most useful to you.

The bottom line

Massachusetts bet that simplifying ADU rules would increase housing production. One year in, that bet is paying off—1,224 new homes approved that wouldn't have existed under the old rules.

But the data also shows that implementation varies wildly by town. Some places have embraced the law. Others appear to be finding ways to slow it down.

Transparency helps. That's why I built this.

We've since gone deeper on the why behind these numbers. Read our consistency gap analysis →

Where Massachusetts fits nationally

One more data point worth noting: ADUs now account for roughly 27% of new single-family residential construction in Massachusetts, ranking the state 11th nationally. That's about 1 in 4 new housing permits.

We dug deeper into how Massachusetts compares to California, the national leaders, and why the state's new tracker only tells part of the story. Read the full analysis →