By Glenn Mathewson
Massachusetts energy code updates: A preview of the future?
Massachusetts has enacted one of the most progressive energy codes in the country. Why should you care if you don’t live there? Here to explain is guest contributor and code educator, Glenn Mathewson.
Massachusetts is leading the way when it comes to building energy code, but it’s not alone. California, Connecticut, and a number of other states have or will be enacting increasingly progressive codes. This means that even if you don’t live in one of these places, you might be interested in knowing where energy code is going next. Here’s a crash course on the ins and outs of Massachusetts energy code.
What is Massachusetts energy code?
In Massachusetts, the current minimum adopted energy code is the 2021 edition of the International Energy Conservation Code (IECC) with amendments. This is what Massachusetts refers to as the “base code,” and there are three methods of compliance:
- The prescriptive method is essentially a recipe for construction, with minimum R-Values for different assemblies and maximum U-Factors for different fenestrations, like windows, doors, and skylights.
- An ERI/HERS score determined by a third-party energy rater to satisfy both government code requirements and voluntary programs like ENERGY STAR is the second method of compliance.
- Meeting passive house standards, either Phius CORE 2021 or Phius ZERO 2021, via verified software from the Passive House Institute and certification by a certified PHI consultant or designer is a third method.
But base code is only the starting point. Municipalities can opt into a second option that’s more progressive, or even a third. Let’s start with the second option, which is called the “stretch code.” It also utilizes the requirements of 2021 IECC with amendments and requires all new dwellings to get an ERI score. As it relates to residential dwellings, the main difference between it and base code is that it doesn’t permit the prescriptive method.
The third and most progressive level of Massachusetts’ building energy code is called “specialized code.” It is considered a net-zero code, but it’s not as simple as it sounds. It requires compliance with the stretch code for both remodels and new construction. For new construction, it also provides a variety of choices for additional efficiency improvements. Compliance methods include zero energy with on-site power production, all electric design, and methods of mixed fuel designs.
Measuring compliance with both stretch and specialized code is a bit complicated and often it’s worthwhile to hire an energy rater or design professional to handle it. For more information about the 2025 Massachusetts building energy code.
Need to back up? Check out Building Code 101 for a primer on how code is created and all the basics.
What is a HERS rating?
To evaluate the efficiency of an entire house, you need a standardized grading method. In Massachusetts, compliance with stretch code is evaluated based on a HERS/ERI score. HERS stands for home energy rating system, and it was developed for this purpose by Resnet, a nonprofit organization. It provides a score on a linear scale drawn between zero and 100. A score of zero is a net-zero house — or a house that generates, through a renewable energy source, as much energy as it uses — and a score of 100 represents efficiency compliant to the 2006 IECC, the newest model code at the time of the HERS creation.
The HERS system is continually reviewed and updated, but the scoring system remains on a scale based on the 2006 IECC. For many years, this energy rating method was useful for tax credits and consumer confidence but was not a method of government energy code compliance. That changed in the 2015 edition of the IECC when the Energy Rating Index (ERI) was added as a method of compliance.
What’s the difference between HERS and ERI?
A HERS score and an ERI score are nearly the same, but much like “model code” and “government code,” A HERS scoring protocol is regularly updated and immediately applicable to the federal programs targeting consumers, such as ENERGY STAR, whereas an ERI score is specific to the government adoption of a particular code edition and edition of the rating standard it references.
Because HERS is a trademarked term belonging to Resnet, the IECC instead references an ERI grade and an American National Standards Institute (ANSI) standard (301-19) detailing the process to determine the rating.
The 2015 IECC designated a new minimum required score for code compliance, lower than the score of 100 in the 2006 IECC. A single design and verification method that can now meet both the code and provide federal consumer incentives was a win-win for builders.
The most recent edition of the IECC, 2024 not only mandates a maximum score of 51 to 54 as code compliant, depending on climate zone and not taking into account on-site power production, but also requires an additional reduction of this score. To simplify this in Massachusetts code adoption, which is all under one climate zone (5A), the code was amended to reflect a maximum score of 42 with fossil fuels and 45 when electric or solar energy is used. This reveals the almost 50 percent increase in minimum required efficiency since the 2006 edition’s passing score of 100.
