Massachusetts Stretch Code Update: Three Key Takeaways

December 7th, 2022


Since the passage of the Green Communities Act of 2008, Massachusetts has followed a Base Building Energy Code detailing minimum energy efficiency requirements. Modeled after the International Energy Conservation Code (IECC), the base code is required to be updated every three years, and is often amended to reflect issues specific to the Commonwealth.

In 2009, Massachusetts added a Stretch Code, which communities can opt to follow in lieu of the base code. The Stretch Code has more stringent energy efficiency requirements to help the state reach its ambitious greenhouse gas emissions goals of a 50 percent reduction by 2030, and net-zero emissions by 2050. According to an article from, “Twenty-seven percent of Massachusetts’ emissions come from onsite combustion of fossil fuels in residential and commercial buildings,” making the commercial and residential guidelines outlined in the Stretch Code an essential part of the Commonwealth’s vision for a green future.

As of November 2021, 299 out of 351 communities have already adopted the Stretch Code, covering 90.3% of the state population, according to data from the Massachusetts Department of Energy Resources (DOER).

As Epsilon reviews the language included in the Stretch Code update, we’ve found a number of small changes that may have a big impact on many projects.

Katie Raymond: My Key Takeaways

As with all code updates, the devil is in the details. A minor tweak here, an added word there, and next thing you know, your project cost just increased 10%. Here, I’ll review what I believe are the three most impactful changes in the new Stretch Code language.

One: Triple Glazing. Everywhere.

All vision (transparent) glass must achieve a maximum whole assembly U-factor (insulative value) of 0.25. While U-factors around 0.25 can technically be achieved with some double-glazed glass, the code update specifies that the framing of the glass and other aspects of the window must also be factored in. The de-rating effects of metal framing negatively impact the window’s insulation quality, bringing the U-factor up. This means that in practice, reaching the whole-assembly 0.25 U-factor with double-glazed windows is virtually impossible, making triple glazing a necessity. Sorry, owners.

U-factor: A measurement of how effectively a window insulates. The lower the value, the better the insulation.
Source: Guide to Energy-Efficient Windows from

Two: Mandatory Electrification

Buildings with greater than 50% “glazed wall systems” (defined as the combination of both vision glass and/or spandrel sections) must employ full electrification of space heating. In other words, if you plan to build a curtainwall building, you may not use fossil fuels for space heating or ventilation air heating. There is an exception for high-ventilation buildings (defined as having average ventilation greater than 0.5 cfm/sf). High-ventilation buildings must use electric systems to satisfy 25% of the building’s peak space heating and ventilation air heating load.

Why Electrification?

Every year, the grid becomes “greener” as renewable power projects come online and supply the grid with energy that is greenhouse gas (GHG)-free. Every year, the GHG “content” of the grid decreases, meaning electric heating systems that are built now will also support reduced GHG emissions each year. Combine electric systems with on-site solar panels and battery storage and you’ve got the formula for a Net-Zero Carbon building. In contrast, the GHG emissions associated with burning fossil fuels on-site for heating will remain elevated and constant for the life of the system.

Three: Air Infiltration Testing Requirement

What used to be an optional added efficiency measure is now a requirement. All new commercial construction must be field tested to ensure maximum air leakage rates are not exceeded. The new code states that buildings over 50,000 sf may test representative portions of the building, but that the following portions of the building shall be tested:

i. The entire building thermal envelope area of stories that have any conditioned spaces directly under a roof.

ii. The entire building thermal envelope area of stories that have a building entrance, a floor over unconditioned space, a loading dock, or that are below grade.

iii. Representative above-grade portions of the building totaling not less than 25 percent of the wall area enclosing the remaining conditioned space.

I read this to say that the entirety of single-story warehouses must be tested. Epsilon has numerous million+ sf single-story warehouse projects. How a million sf can be infiltration tested remains to be seen. But one can only expect this process to be costly and, perhaps more importantly, time consuming.

In Summary

The Stretch Code Update closes a number of loopholes that used to allow for energy tradeoffs in the design of buildings. Teams used to be able to select from a menu of energy efficiency measures that would get the project across the finish line and the selection process was almost always cost-driven. Now, certain measures are prescriptive requirements, and the added cost will be unavoidable. The Stretch Code Update is a bold step towards energy and emissions reductions. But, as in so many industries and communities working to reduce GHGs and respond to our changing climate, it will come at a cost.

Have questions? Please reach out. Epsilon’s team of permitting experts have the answers.

Key Players:

Katie Raymond has more than 25 years of environmental consulting experience focused on greenhouse gas (GHG) mitigation and sustainability. She has become an industry leader in the planning, design, construction, and operation of green buildings. Katie has extensive experience providing GHG, energy efficiency, and sustainability analyses in support of Massachusetts Environmental Policy Act (MEPA) filings for commercial real estate, energy, and other projects. She has a successful track record of achieving client’s sustainability goals through data-driven analysis and innovative problem solving. Ms. Raymond is a Registered Professional Civil Engineer in California and a LEED Accredited Professional.


Learn More:

The Stretch Code update is expected to take effect on July 1, 2023. Projects must file for their building permit prior to that date in order to utilize the current Stretch Energy Code.

Find a summary document of the proposed Stretch Code changes here:

You can find the full proposed Stretch Code update language here:

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