ADU Impact on Housing Production

How first-year ADU permits compare to traditional housing production

150

Towns With Data

12,096

2025 Building Permits

1,224

2025 ADU Approvals

10%

ADU Share of Production

Building Permits: U.S. Census Building Permits Survey (2025 Preliminary) · ADU Permits: EOHLC ADU Survey (Feb 2026)

2025 preliminary data allows same-year comparison of ADU permits and total housing production. Census BPS has a known undercount for Massachusetts — actual production is likely higher. Towns with fewer than 10 reported building permits are excluded from ADU Share calculations.

Town

County

2024 Permits

ADU Apps

Approved

Rate

ADU Share

Bylaws

BostonSuffolk

44 approved·2.5%ADU share

23 approved·2.4%ADU share

6 approved·1.2%ADU share

18 approved·4.4%ADU share

7 approved·2%ADU share

11 approved·3.5%ADU share

6 approved·1.9%ADU share

34 approved·11.6%ADU share

2 approved·0.7%ADU share

9 approved·3.4%ADU share

27 approved·10.3%ADU share

3 approved·1.3%ADU share

2 approved·1%ADU share

6 approved·3.1%ADU share

2 approved·1.2%ADU share

18 approved·11.1%ADU share

6 approved·4%ADU share

North ReadingMiddlesex

2 approved·1.5%ADU share

6 approved·4.6%ADU share

3 approved·2.6%ADU share

26 approved·23.2%ADU share

9 approved·8%ADU share

6 approved·5.6%ADU share

7 approved·6.9%ADU share

7 approved·7.1%ADU share

9 approved·9.8%ADU share

12 approved·13.3%ADU share

1 approved·1.1%ADU share

5 approved·6%ADU share

24 approved·28.9%ADU share

3 approved·3.6%ADU share

5 approved·6.3%ADU share

4 approved·5%ADU share

2 approved·2.5%ADU share

1 approved·1.3%ADU share

MiddleboroughPlymouth

18 approved·23.4%ADU share

7 approved·9.3%ADU share

12 approved·16.2%ADU share

2 approved·2.7%ADU share

10 approved·14.1%ADU share

2 approved·2.9%ADU share

5 approved·7.4%ADU share

6 approved·9.1%ADU share

2 approved·3%ADU share

10 approved·15.4%ADU share

1 approved·1.5%ADU share

13 approved·20.6%ADU share

3 approved·4.8%ADU share

15 approved·25.9%ADU share

1 approved·1.7%ADU share

Showing 1–50 of 221

Does Bylaw Consistency Matter?

Comparing average ADU share of housing production for towns with consistent vs. inconsistent bylaws (among 22 towns with both datasets).

Consistent Bylaws

—%

avg ADU share of housing production

0 towns

Inconsistent Bylaws

11.6%

avg ADU share of housing production

17 towns

Methodology

Building permit data is from the 2025 preliminary Annual New Privately-Owned Residential Building Permits survey, conducted by the U.S. Census Bureau. We use imputed columns that include estimated data for non-reporting and partial-reporting municipalities, providing the most complete picture. Town-level breakdowns use 2024 Census place-level data until 2025 place-level data is available.

ADU data is from the EOHLC ADU Survey, published February 2026, covering the first year of Massachusetts' ADU law (Chapter 150 of the Acts of 2024, effective Feb 2, 2025).

ADU Share of Housing Production = (2025 ADU permits approved) / (2025 total residential units permitted) × 100. This metric compares first-year ADU output against total residential housing production in the same period. Values above 100% indicate a town approved more ADU permits than it issued total building permits.