Introduction
An accessory dwelling unit (ADU) is a small residential living space located on the same lot as another home. A Home for Everyone identifies ADUs as a key ingredient of housing abundance, and the Affordable Homes Act loosened restrictions on this type of homes statewide. Good data about ADU construction is needed to measure progress, assess the impacts to cities and towns, and inform further actions that may be needed to remove barriers or address community impacts. HLC is working with local building officials to collect data on ADU applications and permits issued, as well as to gather information about barriers that still remain for interested homeowners.
ADU Activity since January 2025
HLC contacted building officials in every municipality to request information about ADU applications and permits issued. 2026 data is based on 265 responses to our July 2026 survey of production between January and June 2026. 2025 data is based on mid-year reports in July 2025 and a full year of data in January 2026. 293 municipalities responded to one or both of our 2025 surveys.
Many building officials reported a groundswell of interest in ADUs since the law went into effect. They received over 2,800 applications for ADU building permits since January 2025, and innumerable calls and office visits from homeowners interested in building one.
Municipal officials issued over 2,000 building permits for ADUs in 2025 and the first half of 2026, some of which have already received their certificate of occupancy. The Affordable Homes Act is already delivering new homes that wouldn't otherwise exist.
Homeowners can build an ADU in their backyard, attached to the existing home, or even within the existing building envelope. Statewide, homeowners are taking advantage of all of these options, with half of approvals for detached ADUs and half for attached or interior units. Many homeowners in suburban and rural areas received approvals for detached ADUs, while those in urban communities were more likely to opt for attached or interior ADUs.
Where have ADUs been built?
ADUs have been built all over Massachusetts, in the majority of cities and towns—so far, 246 municipalities told HLC that they had approved at least one ADU. The interactive below provides municipality-level results from HLC's ADU survey, and can be toggled between map and table view and between applications and approvals. Use the filter on the left to select what value to show: number of applications, number of approvals, or percent attached/detached. Use the selector on the right to switch from map to table view. Hover over a municipality to see statistics in a pop-up.
Observations of local building officials
In addition to collecting information about permits issued, HLC asked building officials for their observations about implementation: What is working well? What barriers are homeowners facing? What further state actions could improve the process and facilitate ADU construction? HLC is still reviewing all this feedback, but several themes have already become apparent: First, building officials have noted a groundswell of interest, with multiple inquiries every week (or every day!) from homeowners excited about the prospect of building an ADU for a family member, a caregiver, or a tenant. Many building officials see value in engaging with prospective applicants before they submit a building permit application. These “ADU application review” processes allow municipal staff to guide homeowners through the process of understanding the requirements and preparing complete and approvable permit applications. Several officials also credited their municipal legislative bodies with passing clear ADU bylaws that align with state requirements, thereby reducing conflicts and confusion.
Building officials also described some barriers that some homeowners face on the path to building an ADU. The high cost of construction affects housing development of all types in Massachusetts, and ADUs are no exception. Many report that costs are pushed even higher by the need to expand septic systems, especially where local requirements exceed state standards. Energy code compliance is a major cost driver for some projects, especially those within existing homes. Fire code compliance poses distinct challenges in different ADU types. Attached ADUs must achieve fire separation and sometimes must meet sprinkler requirements as well, while local fire officials sometimes require full-width fire lanes leading to detached ADUs. Some utilities are also requiring separate service connections for water, sewer, and electric, often resulting in unanticipated expense.
HLC and its partners are already working to address many of these issues through new finance products, trainings about landlord tenant laws and more information for homeowners about what it takes to undergo building and renovation projects, and a design competition that will showcase award winning designs and plans. We will continue to analyze feedback from building inspectors and will create opportunities for ongoing consultation. Through coordination with stakeholder groups to identify barriers and opportunities, we will pursue continuous improvement to unlock more ADU production.
Where does this data come from?
Pursuant to the ADU regulations section 71.04, building officials are required to record information about the number, type, location, cost, and size of ADUs applied for and approved; and they must share that information with HLC upon request. During the first 18 years of the ADU program, HLC has surveyed municipal building officials three times: once in July 2025 (seeking information about the first half of the year) and once in January 2026 (seeking information about the full year of permitting), and once in July 2026 (seeking information about the first half of the year. In total, 323 municipalities have responded to at least one survey.
The table below includes results from each municipality. You can download compiled results from each municipality's survey responses at the link below the table.
| Date published: | February 4, 2026 |
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| Last updated: | August 12, 2026 |