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.
