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Map of current energy code adoption in each municipality in MA

Stretch Energy Code & Municipal Opt-In Specialized Building Code FAQ’s

(Information from the DOER)



1. What are the building energy code options for cities and towns in Massachusetts?

Massachusetts cities and towns now have 3 related choices of stringency of building energy code. These are the ‘Base code’ the ‘Stretch code’ and the ‘Specialized code’. The minimum or ‘base’ energy code is the latest version of the national model code – the International Energy Conservation Code (IECC) with some amendments for Massachusetts. The base code is part of the building codes governed by the state Board of Building Regulations and Standards (BBRS). In 2023 the base code is being updated from the 2018 IECC to the 2021 IECC, and MA amendments adding wiring for electric vehicles and maintaining solar ready roof requirements.

2. What is the Stretch code?

The ‘Stretch code’ is a more energy efficient alternative to the base code. The 2023 update is the 3rd major update to the 2009 original Stretch code. The Stretch code increases the energy efficiency requirements for all new residential and commercial buildings, as well as for additions and renovations that require building permits. Municipalities started adopting the Stretch code in 2009; as of January 2023, 300 out of 351 Massachusetts cities and towns have adopted it. The Stretch code is now published and maintained by the Department of Energy Resources.

3. What is the Specialized code?

The Specialized code is required by statute (MGL 25A Section 6) to help achieve MA GHG emission limits and building sector sub-limits set every five years from 2025 to 2050. As a result, all compliance pathways under the Specialized code are designed to ensure new construction that is consistent with a net-zero Massachusetts economy in 2050, primarily through a combination of energy efficiency, that it in turn enables reduced heating loads, and efficient electrification. Use of fossil fuels such as gas and propane or biomass is permitted but comes with additional requirements for on-site solar generation and pre-wiring for future electrification of any fossil fuel using equipment.

4. What is the anticipated cost of building under the Stretch energy code?

Designed and constructed in accordance to Stretch code standards, low-rise residential buildings built with all electric heating and cooling (via heat pumps) will typically cost less to build and operate than those built with fossil fuel heating. One reason for this is that heat pumps can be used for both heating and central air conditioning, whereas fossil fuel heated new homes typically require a separate air conditioning system.

DOER has commissioned studies to analyze the change in construction costs related to building to the Stretch code for several sizes and types of residences, and they generally indicate the construction and operating costs are lower under the Stretch code standards with fully electric heating and cooling via heat pumps. These case studies are available on DOER’s website here:

Analysis of various types of common commercial buildings are also available on the DOER website, though these don’t include an analysis of Mass Save or federal building incentives.

5. How do the base and Stretch codes differ?

The base energy code is currently based on amendments to the IECC2018 national model code but will update to the IECC2021 model code as part of a larger update to the building code as it moves from the 9th edition to the 10th edition. The timing is uncertain but expected at some point in 2023. The base energy code in both the 9th and 10th editions provides two options residential builders may use to meet energy efficiency requirements:

  • Prescriptive Method, installing elements with specific energy efficiency levels (e.g., windows, or wall & roof insulation, furnace, etc.), or

Performance-based Method, building to ensure the home performs to a specific level of efficiency, typically measured through a HERS (Home Energy Rating System) or Passive House analysis, including both of the design plans and the actual built home once construction is completed. The builder can decide how to design the house to reach the performance target.

The Stretch code requires that builders use the performance-based method. Measuring the home in this way brings in a 3rd party energy expert who verifies it is designed and built to perform as expected, which is an important protection for the homeowner and for any future buyer. Some builders in non- Stretch code communities voluntarily choose to use the performance-based method required by the Stretch code because it can often provide greater flexibility.

6. How is the Specialized code different from the Stretch code?

The Specialized code has accelerated adoption of more efficient HERS rating thresholds (HERS 42 and 45) and provides three paths for low rise residential compliance, including a zero-energy pathway (with solar PV). It also requires new homes over 4,000 sq ft to follow the all-electric or zero energy pathway. Solar PV is required for any new construction utilizing fossil fuels for heating. The Specialized code for multi-family housing 4 stories and above phases in Passive House standards by January 2024.

7. Where can I find and read more about the Stretch code and Specialized code?

The Stretch and Specialized codes are new regulations in 225 CMR 22.00 and 225 CMR 23.00. CMR 22.00 covers Residential low-rise construction and CMR 23.00 covers Commercial and all other construction (including most multi-family).

8. What building types does the Stretch energy code and Specialized code apply to?

The Stretch code applies to both residential and commercial new construction, as well as certain renovations and additions. The Specialized code applies only to new residential and commercial new construction.

9. What categories do multi-family residential buildings fall into?

Multi-family building with central heating and cooling are considered commercial buildings. Those that are townhouses and have separate heating and cooling are considered to be low-rise residential buildings.

10. How does the Stretch code apply to historic buildings?

The rules for historic buildings are contained in IECC 2021 C501.5, and state that provisions relating to the repair, alteration, restoration and movement of structures, and change of occupancy are not mandatory for historic buildings provided a report has been submitted to the code official and signed by a registered design professional or representative of the State Historic Preservation Office of the historic preservation authority having jurisdiction, demonstrating that compliance with the provision would threaten, degrade, or destroy the historic form, fabric or function of the building.

11. What is a HERS rating?

HERS stands for ‘Home Energy Rating System,’ and is a national standard that uses information on the design of the energy systems in a home to calculate, via computer modeling, the average energy needs of that home and give it a rating score. The HERS Index was developed by the non-profit Residential Energy Services Network (RESNET) for the mortgage industry and is utilized by the Federal Internal Revenue Service (IRS) and the LEED for Homes program. On the HERS 2006 index scale smaller numbers are better, with 0 representing a net zero energy home, and 100 represents a home built according to meet the national model energy code in 2006 (the IECC 2004 with 2005 amendments). A HERS rating of 52 means that the home uses about 48% less energy than the same size home built to the 2004/2005 IECC code requirements.

12. Do I have to get a HERS rating?

New low-rise residential buildings constructed under the Stretch code will have to get a HERS rating. The HERS performance-based approach provides a very good way to ensure that homes are not only well designed but also well built. As part of the HERS rating the home will be tested for air leakage, and under both the base and the Stretch code homes with heating and cooling ducts may also have those tested for leakage. The HERS rater (Home Energy Raters), builder and building inspector can have confidence that the completed homes really are energy efficient.


Q: How is the stretch code implemented and enforced?

A: Implementation and enforcement of the code is similar to existing code, where the developer is responsible for submitting documentation of compliance to the building inspector for review, and the building inspector conducts a plan and site review. The actual testing is performed by a certified or approved third party (Home Energy Raters).


Q: What is the role of a building code official and a HERS Rater for residential projects?

A: Residential buildings meeting the stretch code through a HERS rating and EPA thermal bypass or thermal enclosure checklist require independent certification by a HERS Rater (Home Energy Raters). The rater will produce a report detailing the energy systems in the building and will provide a HERS index score, together with proof of whether the home qualifies for any federal tax credits. Submission of the HERS report, together with a completed Energy Star Thermal checklist, are the steps required to demonstrate compliance with the energy portions of the code, and must be submitted to the local building inspector prior to receiving a certificate of occupancy. In this way the local inspector retains their oversight role but the additional energy requirements do not place a significant additional burden on their time.