Massachusetts Stretch and Specialized Code Compliance: A Quick Guide for New Construction Projects

In 2023, Massachusetts adopted the 2021 IECC as its base energy code. The residential low-rise Stretch Code went into effect January 1, 2023, and the commercial Stretch Code went into effect July 1, 2023, with a transitional period until 2024.

While the entire state adopted the base code, Massachusetts lets municipalities adopt the Stretch Code or the Opt-in Specialized Code, allowing flexibility of energy efficiency standards locally while still aligning with the state’s greenhouse gas emission reduction and net-zero goals by 2050.

Of the 351 town and cities in Massachusetts, roughly 301 have adopted the Stretch Code and 41 have adopted the Opt-in Specialized Code. (Click here to download the Building Energy Code Adoption by Municipality map from Mass.gov.)

Stretch Code & Opt-in Specialized Code

Residential Section

Low-rise multifamily, attached (townhouse style), and single-family homes fall under the residential section of the code. Compliance is based on the HERS Index Target with additional ventilation, electrical-vehicle-ready, and solar-ready requirements. Passive House is an optional compliance path for residential buildings under the stretch code.

The specialized code is based on the 2021 IECC Appendix RC, Zero Energy Residential Buildings, which requires zero-energy or all-electric buildings, with limited compliance options for electric-ready, mixed-fuel buildings. All compliance options require buildings to be EV-ready as well as either on-site renewables or solar-ready buildings.

Commercial Section

While building size may dictate the appropriate path for commercial projects (including multifamily over three stories), there are five compliance paths:

1. Prescriptive: 2021 IECC with strengthening amendments
2. Targeted Performance: Thermal Energy Demand Intensity (TEDI) limits also based on the 2021 IECC with strengthening amendments
3. Relative Performance: 2019 ASHRAE 90.1 Appendix G using site energy with strengthening amendments
4. Passive House: (certification through Passive House Institute or Phius): Optional for any building type
5. HERS Rating: Home Energy Rating Scores (HERS) certification; optional for multifamily buildings and requiring ENERGY STAR Multifamily New Construction compliance

In addition to the Stretch Code, the Opt-in Specialized Code requires new buildings with any fossil fuel uses or biomass heating to include the following:

• Pre-wiring for future electrification
• On-site solar installations where there is significant available, unshaded roof space
• Passive House certification for residential buildings over 12,000 SF

A Closer Look at the HERS Pathway

The following table illustrates the required HERS score based on project type, fuel usage, and renewable energy.

TABLE R406.5 MAXIMUM ENERGY RATING INDEX

^a Maximum HERS rating prior to onsite renewable electric generation in accordance with Section R405.6
^b The building shall meet the mandatory requirements of Section R406.2, and the building thermal     envelope shall be greater than or equal to the levels of efficiency and SHGC in Table R402.1.2 or Table R402.1.4 of the 2015 International Energy Conservation Code.
^c Alterations, Additions or change of use covered by Section R502.1.1 or R503.1.5 are subject to this maximum HERS Rating, except for Historic buildings which may opt to follow the prescriptive compliance pathway in R401.2.1.

Table notes:

• The first column—new construction until June 2024—is struck through because it was the transition (or grandfather) period for projects to get adjusted.
• Solar electric generation was allowed as a “credit” in previous stretch codes but now it only changes the HERS Index target for renovations/additions.  
• R406.5.2 is the new embodied carbon reduction credit (explained later in this article).
• ADUs, encouraged as part of the housing crisis solution, have an easier HERS target. (Lower is better and harder to achieve in the HERS Index; HERS 0 means the home or dwelling unit produces as much energy, in renewables, as it uses.)

To evaluate code compliance pathways for commercial and multifamily buildings, refer to SWA’s decision tree (click here to download):

3 Requirements for Massachusetts Stretch Code Compliance

In municipalities using the stretch or specialized code, these three requirements will apply to all projects.

Energy Recovery Ventilation is Needed for Compliance

There is virtually no path through compliance without a balanced, energy recovery ventilation system.

For homes and dwelling units to previously meet ASHRAE 62.2 whole unit ventilation requirements, the following strategies were acceptable:

• Exhaust-only where a bath or kitchen fan was set to run continuously or on a timer and pull air through the home or apartment
• Supply-only where fresh air was typically dumped into the heating and cooling system and distributed throughout
• Energy recovery or heat recovery ventilation where the outside air is tempered before being delivered

Exhaust- and supply-only can be part of a balanced ventilation system, and energy or heat recovery doesn’t guarantee a balanced system.

Energy recovery ventilation is required prescriptively, and it’s virtually impossible to make the targeted or performance paths work without balanced, energy recovery.

Project teams must specify an efficient energy recovery ventilator (ERV) or heat recovery ventilator (HRV) with a high total efficiency rating and low watts used per cfm delivered.

Some Type of Third-Party Verification is Required

All buildings require third-party oversight and/or verification including, at a minimum, air infiltration testing and systems commissioning (Cx).

For commercial buildings with larger systems (typically central), Section C408 of the 2021 IECC requires that a plan, systems Cx, and a report are completed by a qualified Cx agent. Heating, cooling, and hot water systems in homes and multifamily dwelling units must also be verified and, in the case of ventilation and ductwork, tested for flow and leakage. These tested numbers, along with air infiltration, are included in the final HERS energy model and affect the final HERS Index.

Project teams must employ a third party. Depending on which code compliance path is being followed, this may include:

• Commissioning agent
• Passive House design consultant and a Passive House rater or verifier
• HERS Rater

Choose 1: Electrification or Massive Carbon Reductions

The stretch and specialized codes aggressively address carbon emissions reduction. To that end, eliminating the use of fossil fuels and combustion-producing equipment and appliances means the code prioritizes all-electric buildings.

Project teams using fossil fuels must install more robust energy efficiency measures (EEMs) such as insulation, windows, equipment, and appliances to compensate. If utilizing the HERS Index path, another way to offset EEMs is by reducing embodied carbon. (Get a more detailed explanation of embodied carbon in our blog post: How to Tackle Embodied Carbon Now: Low-Carbon Building Materials and Assessment Tools.)

To obtain a three-point HERS credit, project teams can meet R406.5.2 by reducing embodied carbon in either insulation or concrete as follows:

• Demonstrate a calculated insulation Global Warming Potential (GWP) intensity (kg CO2e/ft2 ) less than 0
• Demonstrate a calculated concrete mix GWP not more than 70% of the 2022 NRMCA Northeast Benchmark average values

SWA raters work with project teams to identify which EEMs are feasible (i.e., available, constructable, cost effective) for their projects. During this analysis, we have discovered that typically, an all-electric building must install three of the following EEMs, in addition to an efficient ERV or HRV, to meet the HERS 45 target:

1. Continuous insulation on the building’s exterior, typically R7 minimum
2. Triple pane windows with a whole window U value around 0.16 and low (under 0.30) SHGC
3. High-efficiency heat pumps
4. Heat pump dryers
5. Heat pump water heaters

If receiving a three-point HERS credit for meeting embodied carbon reduction, a project might be able to eliminate one of the above EEMs and reduce upfront costs or installation and maintenance concerns.

For example, an electric-resistance water heater is a low-cost, low-maintenance appliance that doesn’t have the space or ducting restrictions of a heat pump water heater. But electric-resistance water heaters, due to their high energy use, typically bump up a HERS Index by at least three points. Since reducing embodied carbon in our building materials is a pressing issue, this may pencil out as a fair swap: reduce the carbon emissions in a major building component (i.e., insulation or concrete) in exchange for installing equipment that’s higher-emitting during the building’s operational stage.

Our Recommendations for Building Owners

• Determine if your municipality requires the Stretch or Opt-in Specialized Code; then determine which code compliance path is required based on your building type and size.
• Engage your third-party consultant early in the design process. If you need Passive House certification or a HERS Rating with ENERGY STAR MFNC Compliance, initial modeling and plan reviews are critical to the project’s success.
• Take advantage of incentives and tax credits. Mass Save provides generous incentives to help offset the cost of meeting these new, rigorous codes. And federal tax credits are available for projects certified to ENERGY STAR or Zero Energy Ready Homes (a PHIUS prerequisite program), or meeting whole building energy savings through ASHRAE 90.1 modeling.

SWA works with project teams at every phase of construction to ensure that buildings are on track to comply with all applicable codes. We can help with every step above; contact us to get started.

Contributor: Karla Butterfield, Sustainability Director