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.  

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.

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.