Methodology & Data Sources
How we collect, classify, and present ADU permit data across Massachusetts.
Disclaimer: This platform provides structured statutory comparison and public-record analysis. It does not render legal opinions or determine enforceability in specific cases. Consult a zoning attorney for project-specific guidance.
📊 Data Sources
Town Permit Portals (Primary)
Our primary data comes from direct scraping of municipal permit portals. We currently scrape active portals for Milton, Plymouth, Duxbury, Newton, Needham, Boston, Andover, Sudbury, Lexington, Falmouth, and Revere. These towns provide permit-level detail including addresses, costs, square footage, and permit status.
EOHLC ADU Survey (Feb 2026)
The Executive Office of Housing and Livable Communities conducted a statewide survey of all 351 Massachusetts municipalities in February 2026. This provides aggregate counts of ADU applications submitted, approved, and denied across 217 responding towns. It does not include permit-level detail (addresses, costs, etc.).
Census ACS & Market Data
Population and housing data uses 2024 American Community Survey estimates. Rent market data is sourced from aggregated listing platforms. Assisted living costs reference the Massachusetts state average of $6,000/month (Genworth Cost of Care Survey).
🔍 What “Tracked” Means
Full permit-level data: addresses, costs, sqft, type, status, notes. Updated weekly. Currently 11 towns.
Aggregate counts only (submitted, approved, denied). From EOHLC Feb 2026 survey. 217 towns total.
On the dashboard map, blue towns have portal-level detail. All other towns show survey-reported aggregate data only.
📋 Definitions
⚖️ Bylaw & Ordinance Consistency Analysis
Town bylaws are subject to review by the Massachusetts Attorney General. Our analysis incorporates published AG disapproval decisions alongside our own provision-by-provision review against Chapter 150 and 760 CMR 71.00.
City ordinances are not subject to AG review. Inconsistencies identified on city pages are based entirely on ADU Pulse's independent analysis of the ordinance text against the same state law standards. These findings are informational, not legally authoritative.
Both town and city analyses use the same methodology: we read the full local ADU bylaw or ordinance, compare each provision against state law, and classify it as Inconsistent, Needs Review, or Consistent. The key difference is the source of authority — AG decisions for towns, our independent analysis for cities.
🔧 Infrastructure Tracker Methodology
The Infrastructure Tracker analyzes local Board of Health septic regulations against the Title 5 state baseline (310 CMR 15.000). Local Boards of Health are authorized under M.G.L. c. 111, § 31 to adopt regulations stricter than Title 5. Exceeding the state baseline is not a legal deficiency — it is an exercise of granted local authority. The tracker documents where local rules create additional constraints for ADU construction.
The local Board of Health rule is stricter than the Title 5 minimum. Legally authorized under M.G.L. c. 111, § 31 — not a deficiency, but a real constraint for ADU design and siting.
A structural obstacle that cannot be addressed through standard design adjustments — for example, a prohibition on variance relief for ADU projects, or a mandatory system type that cannot be substituted.
The provision is ambiguous, unconfirmed, or dependent on local BoH practice that has not been publicly documented. Direct inquiry to the Board of Health is recommended before relying on any assumption.
The local rule matches or is less strict than the Title 5 baseline. No additional constraint identified for ADU projects.
Source methodology: Each town entry is based on primary source documents — the Board of Health's published regulations, not secondary summaries. Documents are retrieved directly from town websites or municipal code aggregators (e.g., ecode360.com) and dated at retrieval. Where regulations reference maps or plans incorporated by reference, those dependencies are noted in the provision detail.
Attorney review: Provisions flagged for legal review are noted with a sourcing note in each town profile. This analysis does not constitute a legal opinion.
Not engineering advice: This analysis documents regulatory requirements. It does not constitute a site evaluation, septic system design, or engineering opinion. Consult a licensed engineer and the local Board of Health before relying on this analysis for a specific project.
🏷️ Confidence Tiers
Each provision in our Consistency Tracker is classified into one of four confidence tiers based on available evidence:
The Massachusetts Attorney General has formally disapproved this provision as inconsistent with state law. This is the highest confidence level — backed by an official government determination.
ADU Pulse's analysis identifies this provision as appearing to conflict with G.L. c. 40A §3 or 760 CMR 71.00, but it has not been the subject of an AG decision. These findings are based on statutory comparison, not official adjudication.
The provision is in a gray area — it may be within the municipality's authority or may face future challenges. Further legal evaluation is recommended.
The provision appears consistent with state law. No issues expected during permitting.
💰 Cost Estimator Methodology
The Cost Estimator uses per-square-foot ranges derived from actual permit data. We segment by ADU type (detached, attached, conversion) and builder type (DIY/homeowner vs. contractor).
Town multipliers adjust for local cost-of-living differences. These are calibrated against actual permit costs where available (e.g., Newton permits typically run 15% above the statewide median, Plymouth 5% below).
The cost breakdown (Building/Labor 65%, Electrical 10%, Plumbing 12%, HVAC 8%, Permits/Other 5%) represents a typical split based on industry benchmarks for residential construction in Massachusetts. Individual projects may vary significantly.
The ROI calculator uses conservative assumptions: rental income at 85% of market rate (accounting for vacancies and below-market ADU pricing), property value uplift percentages derived from appraiser estimates for the local market, and assisted living costs at the Massachusetts state average of $6,000/month.
⚠️ Known Limitations
Incomplete cost data: Not all permits include cost information. Some towns report estimated costs, others report actual construction costs, and some omit costs entirely. Where cost is reported as $0 or missing, we exclude it from averages.
Self-reported survey data: The EOHLC survey relies on municipalities self-reporting their ADU activity. Some towns may undercount (especially smaller communities with manual permitting systems) or misclassify permits.
Portal coverage gaps: We currently scrape 11 town portals. The remaining 340+ towns only have survey-level data. We are actively adding new portal integrations.
Permit ≠ Construction: An approved permit does not guarantee the ADU was built. Some permits expire unused. Our data tracks permitting activity, not construction completions.
Market estimates are illustrative: The ROI calculator, rent projections, and property uplift figures are estimates based on market averages. They are not financial advice. Consult a financial advisor and local real estate professional before making investment decisions.
Questions about our data?
We're committed to transparency. If you spot an error or have questions about how we handle data for your town, let us know.
Get in touch© 2025–2026 ADU Pulse. Data sources include EOHLC, U.S. Census Bureau, Attorney General decisions, and municipal bylaws.