Massachusetts has three building energy code tiers, and which one applies to your project depends entirely on the town where you pull the permit. As of the June 2026 Mass.gov adoption list, 49 municipalities use the Base Code, 242 enforce the Stretch Code, and 60 have opted into the Specialized Code. Here is exactly how they differ — with the current numbers.
The quick comparison
| Requirement | Base Code (49 towns) | Stretch Code (242 towns) | Specialized Code (60 towns) |
|---|---|---|---|
| Legal basis | 10th Edition, IECC 2021 + MA amendments | 225 CMR 22 | 225 CMR 23 (Stretch + Appendix RC) |
| New-home HERS max | No mandate (ERI path available) | 42 mixed-fuel / 45 all-electric | Same, plus net-zero-ready extras |
| Fossil fuels in new homes | Allowed | Allowed (lower HERS cap) | Only under 4,000 sq ft, with electrification pre-wiring + solar; HERS 0 above 4,000 sq ft |
| Multifamily over 12,000 sq ft | Standard commercial paths | HERS or Passive House | Passive House required |
| Heat pumps | Optional | Optional | Required for all-electric homes |
What the Stretch Code requires
The Stretch Code makes a certified HERS rating the primary compliance path for new dwellings: HERS ≤42 (mixed-fuel) or ≤45 (all-electric), up to 48 with embodied-carbon credits, verified by a RESNET-certified rater. It also requires blower door testing (≤3.0 ACH50), duct leakage testing (≤4 CFM25/100 sq ft), balanced ERV/HRV ventilation, EV-ready parking, and solar-ready roofs. ADUs get HERS 52–58; major alterations and additions get 65–75. ENERGY STAR was dropped as a compliance path — HERS and Passive House are the two certification routes.
What the Specialized Code adds
Specialized towns layer Appendix RC on top: three pathways — Zero Energy (HERS 0), All-Electric (heat pumps + HERS ≤45 pre-solar), and Mixed-Fuel (under 4,000 sq ft only, HERS ≤42 pre-solar with electric-readiness wiring, solar, and EV-ready). Ten of these towns (Acton, Aquinnah, Arlington, Brookline, Cambridge, Concord, Lexington, Lincoln, Newton, Northampton) go further still as Fossil Fuel-Free Demonstration communities where gas and oil hookups are generally prohibited in new construction.
How do I know which code my town uses?
Check our Massachusetts Energy Codes guide for the complete town-by-town list with effective dates, or open your town’s page — every one of our city pages (e.g. Quincy, Ashland, Cambridge) states its current code status in the first paragraph. Then get a free quote or call 617-584-1809.
Sources: Mass.gov Building Energy Code Adoption by Municipality (June 2026); 2025 DOER Stretch & Specialized Codes Technical Guidance; Mass.gov Municipal Fossil Fuel-Free Building Demonstration Project.
