Know the code before you build
Massachusetts municipalities enforce one of three energy codes, and the requirements change again by project type and permit date. Two neighboring towns can hold the same house to different standards.
Base Energy Code
The statewide minimum. A shrinking number of municipalities still sit here, and the requirements are the least demanding of the three.
Stretch Energy Code
Adopted by the large majority of Massachusetts municipalities. Compliance normally runs through a HERS rating with a target that depends on fuel type and project type.
Specialized Energy Code
The Stretch Code plus net-zero-ready requirements — wiring for future full electrification, and on-site solar on many mixed-fuel pathways. The hardest of the three to hit late.
Not sure which one your town adopted? Massachusetts publishes the current adoption list by municipality.
Stretch Code HERS targets
These are the targets on the Stretch Code HERS pathway. They are a starting point, not a verdict — your permit date, municipality and project type decide which row actually governs your build.
| Project | All-electric | Mixed-fuel |
|---|---|---|
| Residential new construction | HERS 45 | HERS 42 |
| With R406.5.2 embodied carbon credit | HERS 48 | HERS 45 |
| Accessory dwelling units (ADU) | HERS 55 | HERS 52 |
| Renovations and additions | HERS 70 | HERS 65 |
On renovations and additions, on-site solar generation raises the allowed target by five points (HERS 75 all-electric, HERS 70 mixed-fuel). Reviewed August 2026 against the Massachusetts Stretch and Specialized Code. Codes, municipal adoptions and thresholds change. Confirm the requirement for your specific project before ordering materials or equipment.
It is not only the HERS number that changed
- One EV-ready space with wiring is required per house. Multi-family projects also require EV-ready provision, but the count varies.
- ERV or HRV is now required. Bath fans no longer satisfy whole-house mechanical ventilation on their own.
- HVAC duct leakage testing applies to all systems — including ducts that sit entirely within the conditioned envelope.
- A HERS rating is required for additions over 1,000 sq ft, or over 50% of the original structure (Level 3 Alteration per IEBC).
What compliance support includes
We review your project location, permit timing, plans and proposed equipment to identify the applicable compliance path, then prepare the energy model, testing and documentation the project needs.
- Review of the energy code your municipality has actually adopted
- Preliminary HERS or energy-compliance documentation for the permit set
- A concise list of missing information or recommended changes
- Coordination during construction and technical support for the trades
- Required field inspections and performance testing
- Final compliance documentation for the Certificate of Occupancy
Tell us the town. We will tell you the code.
Send the project address and we will confirm which code applies, what the target is, and what testing the build will need.
Get a Project-Specific Answer