What Is the Massachusetts Stretch Energy Code?
The Massachusetts Stretch Energy Code is an optional but increasingly adopted enhanced building energy code that municipalities can choose to implement in addition to the base Massachusetts Building Energy Code. As of 2025, over 300 Massachusetts cities and towns have adopted it — including virtually all municipalities in Greater Boston, the North Shore, South Shore, and MetroWest regions.
If you’re building anywhere near Boston, there’s a very good chance the Stretch Code applies to your project.
Which Version of the Stretch Code Is Currently in Effect?
Massachusetts adopted an updated Stretch Energy Code based on the 2021 International Energy Conservation Code (IECC). This version took effect for most municipalities in 2023 and introduced more stringent requirements than the previous 2009-based code, particularly around:
- Air tightness (3.0 ACH50 vs the previous 3.0 ACH50 — same threshold, stricter enforcement)
- HERS index requirements for new construction
- Requirements for EV charging readiness
- Heat pump water heater provisions in certain project types
Key Stretch Code Requirements for New Residential Construction
For new residential construction in Massachusetts Stretch Code communities:
- HERS Rating: 55 or below for homes 3,000 sq ft or smaller; 45 or below for homes over 3,000 sq ft
- Blower Door Test: 3.0 ACH50 or better
- Duct Leakage Test: 4.0 CFM25 per 100 sq ft of conditioned floor area or less
- Verified by a Certified HERS Rater: All testing must be conducted and certified by a RESNET-certified HERS rater
Does the Stretch Code Apply to Additions and Renovations?
The Stretch Code primarily applies to new construction. However, additions over 500 sq ft and major renovations may trigger energy code compliance requirements depending on scope. Contact your local building department — and call us — to understand exactly what applies to your project.
What Is the Specialized Opt-In Stretch Code?
Massachusetts also offers a Specialized Opt-In Stretch Code (SOSC), sometimes called the “reach code,” which is even more aggressive. Towns that have adopted the SOSC may require all-electric new construction or have additional requirements beyond the standard Stretch Code. Brookline and several other municipalities have adopted this version.
How to Comply With the Massachusetts Stretch Energy Code
To achieve Stretch Code compliance, your project needs:
- Preliminary HERS Rating — done from plans to verify your design will meet the HERS threshold
- Blower Door Test — conducted after construction is complete
- Duct Leakage Test — conducted at the same time as the blower door test
- Final HERS Rating Certificate — issued by your HERS rater incorporating actual test results
What Happens If You Don’t Comply?
Failure to comply with the Stretch Energy Code means your local building department will not issue a certificate of occupancy. This can significantly delay your project and cause issues with financing, insurance, and sale of the property.
Get Stretch Code Compliance Help Today
Home Energy Efficiency Consultants provides full Stretch Energy Code compliance services across all of Massachusetts. We offer same-day preliminary HERS reports, fast blower door and duct testing, and 24/7 support. Call (617) 501-6788 or visit our contact page for a free quote.
