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.

The encouragement of increased efficiency, through codes and consumer programs, can be taken down to the level of individual components, such as windows. All methods of code compliance, including those in stretch codes, are heavily based on the efficiency of the thermal envelope. The better the envelope, the easier compliance will be with any method. 

To understand the performance of the envelope, a measure called U-Factor x Area (UA) is used to measure a building’s total heat loss. However, in the 2024 IECC, a new similar measure was introduced called Component Performance Alternative where the thermal conductance (TC) of the proposed building is measured slightly differently.