What Stretch Energy Code Means
Stretch Energy Code is an optional appendix to the Massachusetts base building code, designed to incentivize tighter envelope construction. Municipalities adopt by Town Meeting / City Council vote. Once adopted, all new construction + substantial reconstruction in that municipality must meet stretch requirements.
The Three Tiers
| Element | Base (780 CMR) | Stretch (Appendix RB) | Specialized (Appendix RC) |
|---|---|---|---|
| Window U-factor | 0.30 | 0.27 | 0.22 |
| Attic R-value | R-49 | R-49 | R-60 |
| Wall R-value | R-13 + R-5 | R-21 cavity | R-30 (or U-0.040) |
| Basement R-value | R-15 | R-15 | R-19 |
| ACH-50 (infiltration) | ≤ 5 | ≤ 4 | ≤ 3 |
| EV-ready wiring | Optional | Optional | Required |
| Solar-ready conduit | Optional | Optional | Required |
Stretch Code Adopted Municipalities (Sample)
Of 260+ adopted municipalities, the largest by population include:
Greater Boston
Boston, Cambridge, Newton, Brookline, Somerville, Watertown, Belmont, Arlington, Medford, Malden, Quincy, Milton, Dedham, Needham, Wellesley, Weston, Lincoln, Concord, Lexington, Winchester, Woburn, Burlington, Reading, Stoneham, Wakefield.
MetroWest
Framingham, Natick, Wayland, Sudbury, Hopkinton, Holliston, Ashland, Westborough, Southborough, Northborough, Marlborough.
South of Boston
Quincy, Braintree, Weymouth, Hingham, Cohasset, Norwell, Hanover, Pembroke, Duxbury.
Worcester County
Worcester, Shrewsbury, Westborough, Holden, Paxton, Princeton.
Pioneer Valley
Northampton, Amherst, Hadley, South Hadley, Easthampton, Holyoke (parts), Springfield (parts).
Western MA
Pittsfield, Williamstown, Lenox, Stockbridge, Great Barrington.
Full updated list at mass.gov/info-details/stretch-energy-code-development-2023.
Specialized Stretch Code Adopted Municipalities
Newer code (effective 2024). 40+ municipalities adopted as of 2026:
Including: Cambridge, Brookline, Watertown, Newton, Lexington, Concord, Wayland, Sudbury, Lincoln, Carlisle, Acton, Bedford, Belmont — concentrated in Greater Boston suburbs with strong climate-action commitments. Northampton, Amherst, Williamstown also adopted in Western MA.
Specialized Stretch primarily affects new construction and substantial reconstruction projects. Most existing-home retrofits remain under standard Stretch Code requirements.
What This Means for Homeowners
Practical implications by project type:
Window Replacement
In Stretch towns: U-0.27 minimum (Andersen 400 Series HighPerformance, Pella Lifestyle, Harvey Tribute, etc.). In Specialized towns: U-0.22 minimum for new construction; U-0.27 acceptable for replacement on existing homes.
Insulation Upgrade
Mass Save rebated insulation install in any town brings home to current Stretch (R-49 attic) or higher. Specialized targets achievable but require thicker insulation depths.
New Construction
Architects must design to local code from project start. Stretch + Specialized add 3-8% to construction cost vs base code, recouped via lower lifetime energy bills.
Renovation Triggers
'Substantial reconstruction' (typically 50%+ of building value or major envelope work) triggers full current code compliance — including stretch/specialized requirements where adopted. Smaller renovations grandfathered to original code.
Frequently Asked Questions
How do I find out if my specific town has adopted stretch code?
Does stretch code apply to renovations or only new construction?
What's the cost premium for stretch-compliant windows vs base?
Can a town opt OUT of stretch code after adoption?
Does Mass Save rebate stretch-code-compliant windows extra?
How does stretch code interact with historic district requirements?
Will federal energy code preempt MA stretch code?
What's next after specialized stretch?
References & Sources
