Massachusetts Energy Code: Base, Stretch, and Specialized Tiers

The Massachusetts energy code operates in three tiers — Base, Stretch, and Specialized — and every new building or major renovation in the Commonwealth must meet at least one of them. As of May 2026, 243 of the state’s 351 municipalities enforce the Stretch Code, another 59 have adopted the Specialized Code, and fewer than 50 remain on the Base Code alone.¹ Which tier governs your project depends on where the building sits, and the performance targets differ sharply from one tier to the next.

The Three Tiers at a Glance

The Base Energy Code is the statewide floor. It adopts the 2021 International Energy Conservation Code with Massachusetts amendments, codified at 780 CMR Chapter 11R for residential and 780 CMR Chapter 13 for commercial. The current tenth edition took effect on October 11, 2024.²

The Stretch Energy Code is a more demanding standard that a municipality can adopt by vote. Once adopted, it becomes mandatory for every project in that jurisdiction. Low-rise residential rules sit in 225 CMR 22.00; commercial, multifamily, and everything else falls under 225 CMR 23.00.³ Multifamily buildings of four or more stories fall under the commercial code, not the residential one, and that distinction matters because it triggers a different performance framework.

The Specialized Energy Code is the highest tier, aimed at net-zero performance. It layers additional requirements on top of the Stretch Code, including Passive House certification for larger multifamily buildings and a zero-energy pathway for certain homes using fossil fuels. Municipalities can adopt the Specialized Code separately from the Stretch Code.

How to Tell Which Tier Applies to Your Address

Adoption happens municipality by municipality. A project in Cambridge does not face the same rules as one in a rural town still on the Base Code. The Department of Energy Resources publishes a Municipal Energy Code Adoption List, downloadable as a spreadsheet and viewable as an interactive map, showing the tier and effective date for each of the 351 municipalities.¹ Check that list before starting design.

Your local building department can confirm the current status. A jurisdiction can move to a higher tier at any time through a vote of its governing body, so a town that was on the Base Code when schematic work began may have switched by the time you pull a permit. Verify again close to your application date.

Mixed-Use Projects

Buildings that combine residential and commercial spaces are split for code purposes. The residential portions follow the residential energy code, and the commercial portions follow the commercial code.⁴ Under the Specialized Code, residential-use buildings with more than 12,000 square feet of conditioned floor area follow the commercial multifamily requirements, which can mean Passive House certification. A weighted average applies to renewable energy calculations in mixed-use buildings. Getting the classification right early determines the entire compliance pathway.

Residential Requirements: HERS Targets

Residential performance is measured on the HERS index, where 100 represents a standard reference home and zero represents a home that produces as much energy as it consumes annually. Lower is better. The score your project has to hit depends on the tier in effect and the energy systems you install.

Stretch Code

For new construction permits filed after July 1, 2024, the Stretch Code sets these maximum HERS scores before any credit for on-site renewables:⁵

Mixed-fuel building: HERS 42
Building with solar electric generation: HERS 42
All-electric building: HERS 45
All-electric with solar: HERS 45

A three-point embodied carbon credit is available for projects using qualifying low-carbon materials, raising the allowed score to 45 mixed-fuel or 48 all-electric. Accessory dwelling units get more lenient targets in the 52 to 58 range. Major renovations, additions, and changes of use fall between 65 and 75 depending on fuel and solar configuration.⁵

Mixed-fuel homes face the tighter target (42) than all-electric ones (45) by design. A house burning fossil fuels has to make up the emissions difference through a more efficient envelope and better mechanical systems.

Specialized Code

The Specialized Code matches the Stretch Code’s efficiency floor for smaller homes but adds requirements for larger buildings and fossil-fuel users:⁶

All-electric homes of any size: HERS 45, or Phius CORE or Passive House Institute certification. Space heating and water heating must use heat pumps, and appliances must be all-electric.
Mixed-fuel homes under 4,000 square feet: HERS 42 or the Passive House pathway. The building must include electrical service, space, and wiring for future conversion to all-electric.
Mixed-fuel homes over 4,000 square feet: Must follow the zero-energy pathway (HERS 0 including on-site renewables) or the all-electric pathway. A gas stove is still allowed if the building otherwise hits HERS 0.

That last point is where the Specialized Code separates from the Stretch Code. A 4,500-square-foot home with a gas furnace in a Specialized Code town has to hit net-zero energy performance, which in practice means enough rooftop solar to offset annual consumption. The simpler route for most builders is to go all-electric and hit HERS 45.

Commercial and Multifamily Requirements

Commercial buildings, along with multifamily buildings of four or more stories, are governed by 225 CMR 23.00.³ The commercial Stretch Code builds on ASHRAE Standard 90.1-2019 with Massachusetts amendments and addresses mechanical performance, lighting power density, and envelope requirements.

Passive House Threshold for Multifamily

Under the Specialized Code, multifamily projects with more than 12,000 square feet of conditioned residential-use space must achieve precertification through Phius CORE or Passive House Institute standards. The rule phased in by height: five stories or fewer since July 2023, six or more since January 2024.⁶

Passive House demands extreme airtightness (typically below 0.6 air changes per hour at 50 pascals) and very high insulation levels. Structural systems, window specifications, and mechanical ventilation have to be coordinated around the envelope from the earliest schematic phase.

All-Electric vs. Mixed-Fuel Pathway

The Specialized Code offers commercial and multifamily builders two routes:⁶

All-electric pathway: All space heating, water heating, cooking, and drying equipment runs on electricity and meets minimum efficiency standards. This is the simpler route.
Mixed-fuel pathway: Buildings using natural gas, oil, or propane for any heating or appliance must pre-wire and install sufficient electrical service to allow later electrification of all space heating, water heating, cooking, and drying equipment.

The pre-wiring requirement adds construction cost for infrastructure the building will not immediately use. Running conduit and panel capacity during framing is cheaper than retrofitting after the walls are closed.

Documentation for the Permit Application

Any project in a jurisdiction above the Base Code needs detailed energy documentation with the permit application. Residential projects require a preliminary HERS rating from a certified RESNET rater showing the projected index score for the design.³ Commercial projects typically require professional energy modeling reports demonstrating compliance with the applicable ASHRAE or IECC pathway.

The package should include R-values for all insulation, U-factors for windows and doors, and efficiency ratings for every mechanical system, including furnaces, heat pumps, and water heaters. Residential HERS rating services generally run $1,500 to $3,000 depending on size and complexity; commercial energy audits and modeling run higher for large buildings. Finalizing the documentation before submitting the permit application prevents the back-and-forth that delays approvals.

Inspections and Testing

Field inspections at specific construction milestones confirm that the measures shown on paper actually made it into the building. Two tests dominate the residential process.

Blower Door Testing

A blower door test measures envelope airtightness by depressurizing the structure and recording air leakage in air changes per hour at 50 pascals (ACH50). Massachusetts sits entirely within IECC Climate Zone 5A, and the base code caps residential air leakage at 3.0 ACH50. A tight home will test around that level; a very leaky one might hit 10 or more. Projects subject to Passive House under the Specialized Code have to come in below 0.6 ACH50, which demands meticulous air-sealing at every penetration and joint.

Duct Leakage and Mechanical Verification

Inspectors also test the HVAC duct system to confirm that conditioned air reaches the rooms it is supposed to rather than bleeding into unconditioned spaces.³ This test happens before ductwork is concealed behind drywall. Miss the window and you are either opening finished walls or facing a failed inspection.

Once testing is complete, the final HERS rating or updated energy model based on as-built conditions goes to the local building official. The official reviews it against the applicable 225 CMR standards before issuing a Certificate of Occupancy. Massachusetts building code requires that certificate to be issued within ten days of a passing inspection.⁷

What Happens When a Project Fails

If an inspector finds energy code violations during construction, the building official can issue a stop-work order under 780 CMR Section 115, halting activity until the problem is corrected. More often, the official simply refuses to issue the Certificate of Occupancy, which means no one can legally move in or use the building.

For residential builders, a failed blower door test is the most frequent stumbling block. If the building leaks more air than the code allows, the builder has to locate and seal the leaks and then retest. Each cycle costs time and money. On commercial projects, mechanical performance that falls short of the modeled projections triggers a similar loop of corrections and retesting. Treat the energy code as a construction-phase priority, not a punch-list item at the end.

Federal Tax Credits Closing in Mid-2026

Builders of energy-efficient homes in Massachusetts can claim federal tax credits under Section 45L of the Internal Revenue Code, but the window is closing. Under the One Big Beautiful Bill Act signed in July 2025, no credit is allowed for any home acquired after June 30, 2026.⁸

For homes qualifying before that date, the credit amounts are:⁹

Single-family homes meeting ENERGY STAR requirements: $2,500 per unit
Single-family homes certified as Zero Energy Ready: $5,000 per unit
Multifamily units meeting ENERGY STAR requirements: $500 per unit
Multifamily units certified as Zero Energy Ready: $1,000 per unit

For homes acquired in 2026, ENERGY STAR certification must meet version 3.2 of the Single-Family New Homes National Program Requirements, or the applicable regional or manufactured home version.¹⁰ The overlap with the Stretch Code is real: a home built to Stretch standards at HERS 42 to 45 is already close to ENERGY STAR certification, so the incremental cost of qualifying may be small compared to the $2,500 or $5,000 benefit. Construction must be complete and the home sold or leased before July 1, 2026.

On the commercial side, the Section 179D energy-efficient commercial buildings deduction carries the same deadline. No deduction is allowed for property whose construction begins after June 30, 2026.⁸ Confirm eligibility with a tax professional before that cutoff.

1
Mass.gov. Massachusetts Building Energy Code Adoption by Municipality
2
Mass.gov. 2025 Massachusetts Building Energy Codes
3
Mass.gov. 225 CMR 23.00 Massachusetts Stretch Code and Specialized Code for Commercial, Multi-Family and All Other Construction
4
Building Energy Codes Program. How Do Mixed Use Buildings Need to Meet Code
5
Mass.gov. 225 CMR 22.00 Massachusetts Stretch Code and Specialized Code for Low-Rise Residential
6
Mass.gov. Stretch Energy and Municipal Opt-In Specialized Building Code FAQ
7
UpCodes. Massachusetts Building Code 10th Ed Section 111 Certificate of Occupancy and Use
8
IRS. FAQs for Modification of Sections 25C, 25D, 25E, 30C, 30D, 45L, 45W, and 179D Under the One Big Beautiful Bill
9
Office of the Law Revision Counsel. 26 USC 45L New Energy Efficient Home Credit
10
ENERGY STAR. 45L Tax Credit for Home Builders