Specialized Code


The Municipal Opt In Specialized Stretch Energy Code (“Specialized Code”) was developed by the Commonwealth in 2022 as an option for municipalities that wanted to enforce stricter building efficiency standards. It applies only to new construction and requires builders to meet high performance standards and pushes development towards all-electric heating and cooling systems. Lexington Town Meeting passed the specialized code in March 2023, and it goes into effect on January 1, 2024.


There are three levels of building energy codes in Massachusetts: 

  • The Base Code

  • The Stretch Code

  • The Specialized Code

The Base Code is the International Energy Conservation Code (IECC) with Massachusetts-specific amendments. 

In 2009, Massachusetts became the first state to adopt an above-code appendix to the “base” building energy code. The Stretch Code emphasizes energy performance and was designed to result in cost-effective construction that is more energy efficient than that built to the Base Code. The Stretch Code is typically updated every few years, with the most recent update taking effect in 2023. Adopting the Stretch Code is a requirement for participation in the Green Communities program.

The Specialized Code was developed in 2022, following direction from the Commonwealth’s Climate Act of 2021 to develop a municipal opt-in code that advanced net-zero building performance. The Specialized Code builds on the efficiency and clean energy standards in the updated Stretch Code and pushes new construction towards deep energy efficiency, reduced heating loads, consumer protection, and efficient electrification. Learn more about the development of the updated Stretch Code and the Specialized Code.

Specialized Code Summary

The Specialized Code builds off the Stretch Code and only adds requirements to new construction. The Specialized Code is found as an appendix to both the Residential Low-Rise Stretch Energy Code (225 CMR 22.00) and the Commercial Stretch Energy Code (225 CMR 23.00). The Specialized Code can be summarized as follows:

  1. No additional requirements beyond the Stretch Code for additions, alterations, or renovations.

  2. No additional requirements beyond the Stretch Code for all-electric new construction, except for multifamily housing over 12,000 square feet.

  3. Any new residential or commercial construction using fossil fuel combustion systems (except multifamily housing over 12,000 square feet) will need to:

    1. Provide pre-wiring for future appliance and HVAC electrification 

    2. Install a minimum amount of solar (with some exceptions for shading) 

    3. Homes over 4,000 square feet must install enough solar or other renewables to offset ALL of the home’s energy use

  4. Any new multifamily housing over 12,000 square feet will need to meet Passive House standards

Benefits of the Specialized Code


  • All-electric and zero-energy buildings are encouraged, driving new construction closer to net zero emissions.
  • Buildings using fossil fuels must offset usage with onsite solar and must be pre-wired for future electrification. 
  • The energy efficiency requirements of the specialized code result in lower heating and cooling loads in new buildings.


  • The specialized code encourages upfront electrification, helping building owners avoid inevitable costly retrofits down the road.
  • Heating with ground-source or air-source heat pumps in Massachusetts is less expensive than heating with oil or propane. The Applied Economics Clinic found that it will become less expensive than heating with gas, as early as 2026.
  • The vast majority of net zero projects that already exist in Massachusetts experienced a premium cost increase of less than 1%.
  • Forgoing gas hookups in new buildings can save developers thousands of dollars per building.


  • In Massachusetts, buildings are the second most significant source of air-pollution-related premature deaths. Buildings without fossil fuel hookups reduce pollution, both inside and outside.
  • Children living in homes with gas cooking stoves have a 42% higher risk of asthma. The specialized code encourages the use of electric or induction stoves.


What is Passive House?

Passive House is a performance-based building certification that focuses on the dramatic reduction of energy use for space heating and cooling. It results in significantly lower total life cycle costs and minimal additional construction costs, while ensuring healthier, more comfortable, and more resilient buildings. Passive House is being used more and more for affordable housing projects throughout Massachusetts.

Can buildings still have gas cooktops, water heaters or other appliances along with all-electric heating and cooling?

Yes, but this will make the building a “mixed-fuel” building, requiring pre-wiring for future electrification and on-site renewable energy offsets. 

Are emergency generators allowed?

Yes, fossil fuel powered emergency generators are allowed for all building sizes and types. 

Why is there a pre-wiring requirement?

The Specialized Code was developed to be consistent with a net-zero economy by 2050. Wiring for electrification is easy and low cost at the time of construction, but becomes expensive and time-consuming after construction. The pre-wiring requirement protects against high consumer costs for future retrofits, which will be necessary to meet the Commonwealth’s climate goals.

How much solar is required for residential buildings using fossil fuels?

One- and two- family dwellings and townhouses that use fossil fuels must install at least 4kW of solar per dwelling unit, except when the potential solar zone area (refer to code for definition) is less than 300 square feet. Other low-rise residential buildings that use fossil fuels must install on-site solar PV system with a rated capacity of not less than 0.75 W/ft2 of the gross conditioned living area, except when the Potential Solar Zone Area (refer to code for definition) is less than 300 square feet or when the building has a permanently installed domestic solar water heating system with a minimum solar savings fraction of 0.5.

How much solar is required for commercial buildings using fossil fuels?

New buildings that fall under the commercial code and use fossil fuels must install on-site renewable energy with a rated capacity of at least 1.5 W/ft2 of the gross conditioned floor area of the three largest floors. Where the building site cannot meet the requirement in full with an on-site system, the building site shall install a partial system sized to at least 75% of the Potential Solar Zone Area (refer to code for definition).

Are there additional EV charging requirements in the Specialized Stretch Code?

No, there are no additional EV charging requirements beyond the Stretch Code requirements.

Will the Specialized Code hinder affordable housing development?

No. State and federal incentives continue to encourage affordable housing while the Specialized Code delivers benefits for residents. New, all-electric homes are typically less expensive to build than mixed-fuel homes. Affordable housing already represents 44% of all residential net zero and net zero ready square footage in Massachusetts. Most affordable housing development will be multifamily housing larger than 12,000 square feet and therefore required to meet Passive House requirements. Affordable housing developers have been some of the earliest to pursue Passive House, because Passive House buildings provide high-quality housing, lower operational costs, durability, and better air quality. Affordable housing developments that pursue Passive House are awarded additional points to qualify for the Low Income Housing Tax Credit (LIHTC). The Mass Save program also provides incentives for multifamily buildings pursuing Passive House. Check out a complete list of federal and state incentives for multifamily developments pursuing Passive House