Key Takeaways
- • 225 CMR 22.00 Stretch Code (effective 7/1/2024 base; 2025 amendments rolling through April 2026) requires solar-ready provisions.
- • IRC Appendix RB sections RB103–RB106 govern solar-ready zone, mechanical, electrical, and documentation.
- • Solar-ready applies to new construction, additions > 500 sqft, and substantial improvements — NOT simple re-roofs.
- • Mixed-fuel new construction must install 4 kW PV OR preserve a solar-ready zone.
- • Pre-wiring conduit during any re-roof costs $400–$900 vs. $1,400–$3,200 later.
- • Passive House (PHIUS/PHI) certification is an alternative compliance path for new construction.
In This Guide
225 CMR 22.00 at a Glance
Massachusetts operates a two-tier building-energy code: the base code(780 CMR, 10th edition, aligned with IECC 2021 and IRC 2021) and the stretch code(225 CMR 22.00), which any municipality can adopt by Town Meeting or Select Board vote. The base stretch code took effect July 1, 2024, aligning with the state's climate mandates under the 2021 Clean Energy Act. A 2025 amendment package layers on solar-ready provisions, enhanced envelope insulation, and the mixed-fuel/all-electric compliance matrix.
Adoption of the 2025 amendments is rolling through municipalities between January and April 2026. As of this writing (April 22, 2026), roughly 140 of 351 Massachusetts municipalities have formally adopted the 2025 amendments, including almost every municipality in MAPC (Boston metro), several Pioneer Valley and Outer Cape towns, and a handful of Berkshire towns. Enforcement is handled by each local building department with support from the state Department of Energy Resources (DOER).
IRC Appendix RB Solar-Ready Requirements
The 2025 stretch code amendments adopt IRC Appendix RB (Solar-Ready Provisions) essentially in full, with Massachusetts-specific clarifications. The four core sections:
RB103 — Solar-Ready Zone
Minimum 300 sqft contiguous roof area within 45 degrees of true south (preferably 120 degree azimuth cone centered true south). Must be free of obstructions (vents, chimneys, structural projections) and clear of shade from trees, adjacent buildings, or dormers. Zone is documented on permit drawings.
RB104 — Solar-Ready Zone Mechanical
If the home is plumbed for thermal solar, reserved plumbing chases from roof to mechanical room. Most MA homes opt to skip thermal solar preparation and focus on PV; RB104 is then minimal.
RB105 — Solar-Ready Zone Electrical
Minimum 1-inch conduit pathway from the solar-ready zone down to the main electrical panel, terminating with a labeled breaker space sized for the eventual inverter output (typically 40–60 amps for a 5–8 kW PV system). Panel must be main-lug rated or upgraded to support PV backfeed.
RB106 — Construction Documentation
Solar-ready zone must be shown on approved construction documents with dimensions, azimuth, and access paths. HERS rater verifies at plan review and final inspection. Documentation is retained by the building department.
When Your Project Triggers Compliance
In a municipality that has adopted the 2025 stretch code amendments, compliance triggers vary by project type:
| Project Type | Solar-Ready Required? | Notes |
|---|---|---|
| Like-for-like re-roof | No | Best practice: pre-wire conduit while deck is open. |
| Re-roof + addition < 500 sqft | Limited | Full stretch code applies to addition portion. |
| Re-roof + addition > 500 sqft | Yes | Full 2025 stretch code including solar-ready. |
| New construction | Yes | Full RB103–RB106; mixed-fuel triggers 4 kW rule. |
| Substantial improvement (> 50% valuation) | Yes | Treated as new construction for code purposes. |
| Change of use (commercial to residential) | Yes | Full stretch code applies. |
The "substantial improvement" threshold (50 percent of pre-improvement valuation) is the most commonly misunderstood trigger. If your project total exceeds half the property's assessed value, the entire building is subject to the full stretch code, including envelope and solar-ready provisions, not just the scope of work. This disproportionately affects older inexpensive homes in gentrifying areas. Always run a pre-application cost vs. assessed-value check before finalizing scope.
Price a Solar-Ready-Compliant MA Roof
Get an instant quote from pre-vetted MA contractors who handle 225 CMR 22 compliance, HERS coordination, and solar-ready pre-wire during re-roof.
Towns That Have Adopted 2025 Amendments
Illustrative list of MA municipalities that have formally adopted the 2025 stretch code amendments (as of April 2026). DOER maintains the definitive public spreadsheet at mass.gov/info-details/stretch-code-adoption.
Greater Boston / MAPC
Boston, Cambridge, Brookline, Somerville, Newton, Arlington, Lexington, Concord, Belmont, Watertown, Medford, Malden, Revere, Quincy, Waltham, Needham, Wellesley, Natick, Framingham, Acton, Sudbury, Lincoln
Pioneer Valley & Western Mass
Amherst, Northampton, Easthampton, Great Barrington, Stockbridge (+ several pending Town Meeting votes in spring 2026)
Outer Cape & Islands
Provincetown, Truro, Wellfleet, Eastham, Aquinnah, Chilmark, West Tisbury
Still on Base Stretch (pre-2025)
Plymouth, Bridgewater, Brockton, Taunton, Fall River, New Bedford, Fairhaven, Dartmouth, Webster, Milford, Fitchburg, Leominster, Gardner, Athol, Orange
Mixed-Fuel New Construction 4 kW Rule
For new construction using fossil fuel for any primary end-use (natural gas, propane, or fuel oil for space heating, water heating, cooking, or clothes drying), the 2025 amendments require one of two compliance paths:
- • Path A — Install 4 kW PV: A minimum 4 kW nameplate photovoltaic system installed and commissioned at certificate of occupancy. System offsets roughly 5,000 kWh/year of grid electricity in MA climate.
- • Path B — Preserve Solar-Ready Zone: Document an activatable solar-ready zone per RB103–RB106 sized to host at least a 4 kW system. Homeowner can install PV later.
All-electric new construction (no fossil fuel end-uses) is exempt from the 4 kW rule because the home's per-square-foot energy intensity already beats the mixed-fuel baseline under the stretch code performance calculations. Many MA builders in adopting towns are opting for all-electric to avoid the dual PV + solar-ready overhead, paired with cold-climate heat pumps (Mitsubishi Hyper-Heat, Daikin Aurora, Fujitsu Halcyon) that perform down to −15°F.
Stretch Code Compliance Checker
Select your year built, project scope, and town. The checker identifies whether your project triggers solar-ready compliance and outlines the pathway.
Stretch Code Compliance Checker
Verify whether your re-roof, addition, or new construction triggers 225 CMR 22 2025 stretch code solar-ready provisions in your MA town.
Applicable code: 225 CMR 22 + 2025 Amendments (Stretch Code)
Est. cost uplift during re-roof: $400–$900
Compliance Pathway
- 1. Re-roof alone does NOT trigger 2025 stretch code solar-ready mandate
- 2. Pre-wire solar conduit during re-roof for $400-$900 — low-cost future-proofing
• If your re-roof is part of a larger scope (addition, HVAC swap) crossing substantial-improvement, the mandate can apply.
Illustrative guidance based on 225 CMR 22 2025 amendments and IRC Appendix RB. Town adoption status is updated periodically; verify with your local building department before permit application. Not a substitute for code-official review.
Cost Uplift During Re-Roof vs. Later
When the roof deck is already open, adding solar-ready provisions is nearly free labor — the electrician is onsite for other coordination anyway, and a conduit run of 30–60 feet takes 2–4 hours. Retrofitting the same work after the roof is closed requires fishing conduit through finished ceilings and walls, partial drywall cuts, and often a second electrician visit for the panel tie-in.
| Scope | During Re-Roof | After Roof Closed Up |
|---|---|---|
| 1-inch PV conduit, attic to panel | $300–$550 | $900–$1,600 |
| Labeled breaker space + panel tie-in | $100–$250 | $250–$500 |
| Roof penetration boot + flashing | Included in re-roof | $250–$600 |
| Permit + inspection | Bundled | $0–$500 |
| Total | $400–$900 | $1,400–$3,200 |
Passive House Alternative Path
The 2025 amendments recognize Passive House Institute US (PHIUS) and Passive House International (PHI) certification as an alternative compliance path for new construction. Certified Passive House buildings' whole-building energy use intensity (EUI) already beats the stretch code performance baseline, so they are exempt from the 4 kW solar-ready-or-installed provision (though the solar-ready zone provisions of RB103 still apply for future flexibility).
Passive House is largely a new-construction strategy. For re-roofs and additions, HERS path + solar-ready is cheaper and simpler than Passive House retrofit. For new single-family construction, Passive House costs 4-10 percent more than conventional stretch-code-compliant construction but operates at roughly one-quarter the annual energy cost, which appeals to buyers targeting long-term efficiency.
Frequently Asked Questions
Frequently Asked Questions
Does a simple re-roof trigger the 2025 stretch code solar-ready requirement?
No. A like-for-like re-roof (same footprint, same slope, no addition, no substantial improvement crossing the 50-percent-valuation threshold) does not independently trigger solar-ready requirements even in a town that has adopted the 2025 stretch code amendments. Solar-ready provisions (IRC Appendix RB, sections RB103-RB106, as adopted through 225 CMR 22) apply to new construction, additions over 500 sqft, and substantial improvements. That said, most MA contractors now recommend adding $400-$900 of pre-wired solar conduit during any re-roof in a stretch-code town because the marginal cost is tiny and the future installation complexity drops significantly. If you later bundle your re-roof with an addition, HVAC swap, or basement finish that pushes the cumulative project across the substantial-improvement threshold, the whole project can retroactively require solar-ready compliance.
Which Massachusetts towns have adopted the 2025 stretch code amendments as of April 2026?
Adoption is rolling throughout 2025 and 2026. Greater Boston, Cambridge, Brookline, Somerville, Newton, Arlington, Lexington, Concord, Belmont, Watertown, Medford, Malden, Revere, Quincy, Waltham, Needham, Wellesley, Natick, Framingham, Acton, Sudbury, and Lincoln have adopted. Pioneer Valley towns that have adopted include Amherst, Northampton, and Easthampton. The Berkshires include Great Barrington. Outer Cape and Islands towns Provincetown, Truro, Wellfleet, Eastham, Aquinnah, Chilmark, and West Tisbury have adopted. Towns still operating under the base 225 CMR 22 (pre-2025 amendments) include Plymouth, Bridgewater, Brockton, Taunton, Fall River, New Bedford, Fairhaven, Dartmouth, Webster, Milford, Fitchburg, Leominster, Gardner, Athol, and Orange. Always verify with your local building department — Town Meeting and Select Board adoption timelines vary and the full list grows monthly. DOER maintains a public spreadsheet of adoption status.
What exactly is a RB103 solar-ready zone?
IRC Appendix RB section RB103 defines the solar-ready zone: a clearly designated area on the roof, minimum 300 sqft of contiguous surface, oriented within 45 degrees of true south (ideally within 15 degrees), free of obstructions like vents, chimneys, and shade from trees, dormers, or adjacent structures. The zone must be documented on permit drawings with dimensions and clear access pathways. On a typical new-construction colonial in MA, the south-facing main-roof plane almost always satisfies this. On a contemporary or split-level with a gable facing east-west, designers often specify a rear-facing zone or a dedicated solar-ready roof cricket. Your builder's HERS rater verifies the zone during plan review and again at final inspection. The zone does not have to be activated with actual PV modules at construction — it just has to be preserved for future installation.
Do I need a HERS rater for a re-roof in a stretch-code town?
Only if the re-roof is part of a larger scope triggering the stretch code. For new construction, additions over 500 sqft, and substantial improvements, a HERS (Home Energy Rating System) rater must be engaged by the project team. The rater performs two verifications: (1) plan review before permit issue, confirming the solar-ready zone, electrical pathway, and mechanical reservations are shown; (2) on-site inspection at or near the final building inspection, confirming the scope was actually installed. HERS rater fees for a residential project typically run $800-$1,800 depending on square footage. For a pure re-roof without additional scope, no HERS rater is required. For a re-roof bundled with an addition under 500 sqft, HERS scrutiny is usually limited to the addition only.
What is the "mixed-fuel" 4 kW minimum PV requirement for new construction?
Under the 2025 stretch code amendments for mixed-fuel new construction (homes using fossil fuel for any primary end-use: space heating, water heating, cooking, clothes drying), builders must choose one of two compliance paths: (a) install a minimum 4 kW photovoltaic system at time of construction, OR (b) document and preserve an activatable solar-ready zone under RB103-RB106 that can host at least a 4 kW system. Option (b) is the more common path because it lets the builder preserve margin and lets the homeowner defer the PV investment. All-electric new construction (following the stretch code all-electric path) is exempt from the 4 kW solar-ready-or-installed provision because the home already has lower per-square-foot carbon intensity. See 225 CMR 22.00 section 11.0 (as amended) for the full compliance matrix.
How much does it cost to add solar-ready provisions during a re-roof vs. later?
During a re-roof, adding solar-ready provisions runs roughly $400-$900 for a simple pathway install (1-inch conduit from designated zone to electrical panel, labeled breaker space, preserved 300 sqft zone): your roofer or electrician spends 2-4 hours on conduit routing while the roof is already open. Doing the same work after the roof is closed up and drywall is finished typically runs $1,400-$3,200 because conduit has to be fished through finished walls, the roof may need partial disturbance, and the electrician must work around existing mechanicals. The 3-4x markup is the single strongest argument for pre-wiring during any re-roof in a stretch-code town even when not legally required.
Can I use the Passive House alternative path for solar-ready compliance?
Yes. The 2025 stretch code amendments offer a Passive House Institute US (PHIUS) or Passive House International (PHI) certification pathway as an alternative compliance option for all-electric new construction. Certified Passive House projects are exempt from the 4 kW solar-ready-or-installed provision because their whole-building energy use intensity (EUI) target is already well below the code baseline. For major renovation and addition projects, Passive House is usually impractical to retrofit, but for new construction it's a strong option where the homebuyer or builder already targets best-in-class performance. The Passive House path requires third-party PHIUS/PHI certification rather than just HERS verification.
Does the stretch code apply to commercial roof replacements?
Yes, for commercial buildings the 2025 stretch code amendments for commercial construction (adopted in parallel with the residential updates) include enhanced envelope requirements and, for new commercial construction over 10,000 sqft, solar-ready provisions. Commercial re-roof projects that cross the substantial-alteration threshold may trigger envelope upgrade requirements even when not explicitly solar-ready related. For commercial TPO or PVC re-roofs that also add insulation (continuous above-deck rigid foam), the stretch code's R-values for climate zone 5 (most of MA) require R-30 to R-35 above deck for low-slope roofs, depending on construction type. Commercial owners should engage a code consultant on any project over 5,000 sqft in a stretch-code town.