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What is a building code?

Clean Heat, Clean Air | Educational Building Block #5

Welcome to the Massachusetts Clean Heat, Clean Air campaign educational building block series! This series was created by Mothers Out Front members to share key concepts and terms from our campaign for healthy homes & communities. These building blocks are intended to be short, easy learning opportunities for busy advocates.

Building codes have a long and dynamic history. They are ancient, written into the Bible and Hammurabi’s Code. The first American building code was enacted in Boston in 1631 when the Governor outlawed thatched roofs and wooden chimneys, for reasons you can doubtless imagine.

Today, building codes are a powerful tool that can either transform our buildings into a climate solution – or maintain buildings’ current status as an enormous contributor to climate change.

Building codes reflect societal values, our need for safety and for comfort, and, in this moment of the climate crisis, they must soon reflect our commitment to a livable future.

Plimoth Patuxet old buildings

Thanks to building codes, these fire-traps have been illegal in the Commonwealth for almost 400 years.

Image Source: David L. Ryan, The Boston Globe

What is a building code?

Building codes set standards for the design, safety, and materials of buildings. Our state’s building code is hundreds of pages long and covers every element of a building from “Soils and Foundations” to “Roof Assemblies and Roof Structure”.[1]

Pertaining to energy specifically, Massachusetts currently has two building codes that communities can choose to adopt. The base code sets minimum standards and serves as a “floor”, while the stretch code is the “ceiling” beyond which communities cannot make any further building requirements. The base code is derived from the International Energy Conservation Code. The stretch code, currently approved by the Massachusetts Board of Building Regulations and Standards, allows communities to require more energy-efficient construction standards. Building codes are set at the state level – local municipalities can’t design and require local codes. Statewide building codes ensure an efficient approach to ensuring that buildings are constructed to approved standards.

Building codes and climate change

Buildings account for approximately 40% of global carbon emissions.[2] If you’ve ever lived or worked in a drafty old building you know they can be uncomfortable and expensive to heat and cool. Buildings last decades, if not centuries, so if we are preparing for a sustainable future we need codes that lead the way.

infrared scan of inefficient old house -- karen pollard

Older homes often have less efficient windows and walls than new construction – and many other features that would not be considered up-to-code by today’s standards.

Image Source: Old House, Karen Pollard

In 2009, Massachusetts became the first state in the nation to create a stretch code that reached beyond the existing building code to require more energy efficient buildings. Today, almost 90% of Massachusetts residents live in a community that has adopted the stretch code.[3]

Sometimes, however, building codes don’t keep up with new design and technology. Let’s say, for example, that your building code says that your roof needs to be made of sticks and not straw – but it also can’t be built from new, high-performance bricks because they didn’t exist when the code was written. Or perhaps your building code still encourages buildings heated with oil, propane, and natural gas, or buildings constructed with large amounts of high-emitting materials like cement.

In Massachusetts, the “ceiling” offered by the stretch code is so low that it is no longer a true stretch code due to changes in technology and our statewide mandate to reach net-zero emissions by 2050. While the state’s base code is updated every three years, our stretch code hasn’t been fully updated in over a decade.[4]

diagram of zero emission building City of Boston

In 2020, the City of Boston Department of Neighborhood Development released a “Guidebook for Zero Emission Buildings”. To reduce building emissions, the Guidebook calls for buildings to increase efficiency, convert nearly everything that runs on fossil fuels to run on electricity, and buy 100% clean energy. [5] Developers receiving City funding for affordable housing must meet the guidebook’s standards.[6]

A new, specialized stretch energy code for Massachusetts

In March 2021, Massachusetts enacted sweeping new climate change legislation, colloquially known as the “Next-Generation Roadmap”. Among many other requirements, the law mandates the creation of a new, more stringent opt-in stretch code by 2022. The exact language is wonky but important, so please bear with us for a moment:

The Department of Energy Resources will “develop and promulgate, in consultation with the state board of building regulations and standards, a municipal opt-in specialized stretch energy code that includes, but is not limited to, net-zero building performance standards and a definition of net-zero building, designed to achieve compliance with the commonwealth’s statewide greenhouse gas emission limits and sublimits…”[7]

In addition to the net-zero performance standards and definitions, the new law also moves development of this new stretch code over to the Department of Energy Resources (DOER), requires at least five public community input sessions, and adds four new seats to the existing Board of Building Regulations and Standards (BBRS) for experts in energy efficiency and advanced building technology.

illustration of net zero building Efficiency Vermont

A net-zero building is highly efficient and produces as much renewable energy as it consumes.

Image Source: Efficiency Vermont – click on image to enlarge the photo and for more detail

The Department of Energy Resources has a two-part strategy for updating the stretch code. The first phase will be an update to the existing stretch code. Any changes to the existing stretch code will become automatic in July 2021 for the many communities that have already adopted it. The second phase will be the development of the new opt-in stretch code mandated by the Roadmap bill, with meetings announced over the summer and community input beginning in the fall.

All of this is exciting progress! However, as you may have noticed, there are two big steps to come:

  1. Ensuring that the new opt-in stretch code is as ambitious and well-designed as possible, so the code is a true net-zero code.
  2. Mobilizing community advocates and local decision-makers to learn about net-zero buildings and stretch codes to gain local support and commitments to opting-in to the new stretch code when it is released.

A key element of the Clean Heat, Clean Air campaign will be working with our allies to ensure that we have a future-ready building code and that as many towns and cities in the state as possible join the movement.

all-electric boston townhomes -- placetailor

Net-zero, all-electric townhomes in Boston’s Fort Hill neighborhood.

Image Credit: Placetailor

Deep Dive

Amherst living building -- Hampshire college

The R.W. Kern Center at Hampshire College in Amherst, MA is a certified “living building.” The Center produces its own electricity, treats its own water, and is built with non-toxic, low-carbon materials.

Image Credit: Hampshire College

Meet our Allies: Massachusetts Climate Action Network

Massachusetts Climate Action Network is an advocacy organization that works with its 60+ chapters around the State on clean energy, energy efficiency, and energy justice efforts at the local level. MCAN mobilizes local advocates to push for state-level legislative and regulatory efforts that move the Commonwealth to net-zero by 2050. MCAN’s Affordable Housing is a Climate Solution campaign puts housing affordability in the center of their net-zero stretch code work. Learn more by signing up to receive MCAN’s newsletter here.


[1] “The Massachusetts State Building Code (MSBC) consists of a series of international model codes and any state-specific amendments adopted by the Board of Building Regulation and Standards (BBRS). The BBRS regularly updates the state building codes as new information and technology becomes available and change is warranted. The MSBC is separated into two distinct volumes: The Residential volume regulates all one- and two-family structures and townhouses that are three stories or less, as well as their accessory structures; The Base volume regulates all structures that are not covered by the Residential regulations.” (text from:


[3] Under the 2008 Green Communities Act, municipalities must adopt the stretch code to become a designated Green Community (and be eligible for associated funding). Massachusetts has 280 designated green communities and 289/351 MA communities have adopted the stretch code