225 CMR 23: Massachusetts Stretch Code and Specialized Code

225 CMR 23.00 is the Massachusetts Stretch Energy Code, and its optional Specialized Code overlay, for commercial buildings, multi-family residential buildings, and all other construction outside the scope of the low-rise residential code. Administered by the Department of Energy Resources, it replaces the base state energy code in any municipality that adopts it, and sets stricter energy performance standards on new construction and, for the Stretch Code portion, on additions, alterations, and changes of use. The most recent amendments took effect on February 14, 2025, aligning the regulation with IECC 2021 and ASHRAE Standard 90.1-2019.1Mass.gov. 225 CMR 23.00 Massachusetts Stretch Code and Specialized Code for Commercial, Multi-Family and All Other Construction

What Buildings 225 CMR 23.00 Covers

The regulation applies to commercial buildings, multi-family residential buildings, and all other construction that falls outside 225 CMR 22.00 (which handles low-rise residential: generally single-family homes, duplexes, and townhomes). Both new construction and renovations are within scope, including additions, alterations, and changes of use.1Mass.gov. 225 CMR 23.00 Massachusetts Stretch Code and Specialized Code for Commercial, Multi-Family and All Other Construction

The Stretch Code is not automatically statewide. Whether it governs your project depends on the municipality. Any city or town seeking Green Community designation must adopt it, and every Green Community has. As of 2025, 298 Massachusetts cities and towns hold that designation.2Mass.gov. Becoming a Designated Green Community In those municipalities, 225 CMR 23.00 stands in for the base energy code. If your project sits in a non-adopting municipality, the base code in 780 CMR still applies instead.3Mass.gov. Building Energy Code

HERS Index Thresholds for Multi-Family Buildings

For multi-family buildings, compliance is measured through the Home Energy Rating System (HERS) Index. Every dwelling unit has to score at or below the maximum HERS Index set by the code. For new construction with permits issued after July 1, 2024, the ceilings are:

  • Mixed-fuel buildings: HERS Index of 42
  • All-electric buildings: HERS Index of 45
  • Mixed-fuel with solar: HERS Index of 42
  • All-electric with solar: HERS Index of 45

The score is measured before any credit for on-site renewable generation, so the envelope and mechanical systems have to hit the number on their own. Multi-family projects must also meet or exceed ENERGY STAR Multifamily New Construction program requirements.

Solar-Ready Zones and Storage-Ready Space

New commercial buildings of five stories or fewer must include a solar-ready zone on the roof. The zone has to cover at least 40 percent of the roof area, calculated as the gross horizontally projected roof area minus skylights, occupied roof decks, vegetative roof areas, and required setbacks. No sub-zone can be narrower than five feet in its shortest dimension.

Structural design has to carry a collateral dead load of at least five pounds per square foot in the solar-ready zone. The main electrical service panel must reserve space for two dual-pole circuit breakers, one for a future solar electric system and one for a future energy storage system, both labeled “For Future Solar Electric and Storage.” A designated floor area for the future electrical storage system, at minimum two feet by four feet, must be shown on the construction drawings and sited to comply with the fire code. A building that already includes a permanently installed renewable energy system is exempt from the solar-ready zone requirement.

Electric Vehicle Ready Parking

New parking spaces need to include EV-ready capacity. The Specialized Code addresses this in Section CC101.5, which points back to the EV-ready requirements in Section C405.13.4Legal Information Institute. Massachusetts Code 225 CMR 23 CC101 – General Multi-family properties may follow either the commercial EV-ready requirements in C405.13 or the residential provisions in 225 CMR 22.00, which call for at least 20 percent of parking spaces to be wired with a 40-amp, 208/240-volt circuit capable of Level II charging. Each EV-ready circuit has to be labeled in the service panel and terminate within six feet of the designated parking space.

Renovations, Alterations, and Changes of Use

The Stretch Code applies to existing buildings undergoing additions, alterations, or changes of use, with somewhat relaxed HERS thresholds. Mixed-fuel multi-family renovations face a HERS Index ceiling of 55, and all-electric renovations with solar have a ceiling of 61, with intermediate values for the other fuel and solar combinations. A gut renovation or change of use triggers Stretch Code compliance, but the numbers acknowledge the constraints of working inside an existing structure.

The Specialized Code, by contrast, does not apply to existing building work. Renovation projects only need to meet the Stretch Code, not the Specialized Code overlay, even in municipalities that have adopted both.

When the Specialized Code Adds Requirements

Municipalities may adopt the Specialized Code on top of the Stretch Code. Where they do, new construction has to meet 225 CMR 23.00 and then satisfy one of three additional compliance pathways under Appendix CC:4Legal Information Institute. Massachusetts Code 225 CMR 23 CC101 – General

  • Zero Energy Pathway: the building qualifies as a zero energy building. If it uses any on-site fossil fuel, it must also be pre-wired for future electrification of all fuel uses.
  • All-Electric Pathway: the building uses no on-site fossil fuels. No additional measures beyond the Stretch Code standards are required.
  • Mixed Fuel Pathway: buildings that are not zero energy and use on-site fossil fuels must satisfy both pre-wiring requirements for future electrification and additional energy performance provisions. Backup generators and on-site vehicle refueling are not counted as fossil fuel use for this determination.

The Specialized Code also requires Passive House certification for multi-family buildings larger than 12,000 square feet. Mixed-fuel commercial buildings must install a solar photovoltaic system rated at least 1.5 watts per square foot across the three largest floors. Where site constraints make full compliance impossible, a partial system covering at least 75 percent of available roof space is accepted.

Figuring Out Which Chapter Governs Your Project

The line between 225 CMR 22.00 and 225 CMR 23.00 is building type. Low-rise residential (single-family, duplex, townhome) sits under 22.00. Commercial, larger multi-family, and everything else sits under 23.00.5Mass.gov. 2025 Massachusetts Building Energy Codes Municipalities that adopt the Stretch Code adopt both chapters together, and the Specialized Code splits the same way, with Appendix RC layered onto 22.00 and Appendix CC layered onto 23.00. Identifying the correct chapter before choosing a compliance pathway matters, because the performance thresholds and documentation differ between the residential and commercial sides.