This article is a paper presented at the 27th International Passive House Conference 2024 in Innsbruck
Author: Paul Ormond, Beverly Craig

The Commonwealth of Massachusetts now has a building energy code which allows municipalities within Massachusetts to mandate Passive House for new residential buildings over 12,000-sf within their jurisdictions [DOER, 2022]. Over 25% of Massachusetts’ population now lives in one of these communities [DOER, 2024]. Over 14,000 Passive House dwelling units have been built or are underway [Craig 2024]. Just 4 years ago, Massachusetts had just two Passive House buildings [Simmons 2022]. This article provides the story on how this mandate and tremendous adoption of Passive House came to be.

To understand the Massachusetts story, it’s helpful to first understand two notable acts passed by the Massachusetts state legislature aimed at addressing decarbonization. The first notable act was the Green Communities Act (GCA) [Massachusetts 2008]. It’s difficult to overstate how important this act was in advancing building energy codes in Massachusetts. The GCA allowed the state energy office, the Department of Energy Resources (DOER), to create two tiers of building energy codes: a “Base Code” and an optional, more ambitious, “Stretch Code”. Each municipality within the state would have to follow at least the Base Code but would have the option of mandating the Stretch Code within their jurisdiction. Because of its optionality, the Stretch Code became a key mechanism for including more ambitious energy efficiency provisions within the code.

The passage of the GCA immediately created an active constituency, literally thousands strong, of Massachusetts “citizen-advocates” that organized to bring the Stretch Code to their municipality. Municipalities were incentivized to adopt the Stretch Code because adoption entitled the municipality access to significant funding for building renovations under the state’s “Green Communities Program”. Since 2008 a total of 301 municipalities (over 85% of all municipalities) adopted the Stretch Code [DOER 2024].

Notably, in the course of their advocacy, many of these citizen-advocates became quite knowledgeable about building codes and how improved codes can address climate change via building decarbonization. The GCA transformed local citizens across Massachusetts that cared about climate change, but perhaps didn’t know “what they could do about it”, into active, knowledgeable, and motivated building energy code advocates.

The second notable act was passed in 2021 following GCA’s success. This was the Next Generation Roadmap Act (NGRA) which created a third, even more ambitious, optional building energy code available for municipal adoption which came to be known as the “Specialized Code” [Massachusetts 2021]. The Specialized Code mandates Passive House for residential buildings over 12,000-sf. This code also contains requirements related to building electrification.

Having had more than a decade of experience with adoption of optional codes, municipalities and citizen-advocates were highly organized to rapidly bring the Specialized Code, and thus the Passive House mandate, to their community. Citizen-advocates had become familiar with Passive House and knew the benefits that Passive House can bring to the communities. Within a year of becoming available, four major cities and 27 other smaller communities adopted this tier, comprising 25% of Massachusetts population [DOER 2024]. Each month brings additional adoption.

Massachusetts’ Passive House story is not complete without understanding building space heating and the electric grid. Rapid transition to a renewably generated electric grid has created new opportunities to decarbonize building space heating by swapping from fossil fuel to electric. However, this swap has been met with concerns about imposing new demands on an already stressed electric grid.

In local vernacular, Passive House is described as something that “crushes” space heating. This is because it doesn’t just reduce space heating incrementally, but near eliminates it [Zimin 2022]. Passive House’s ability to “crush” building space heating to near elimination enables a “grid friendly” swap from gas to electric space heating, unlocking decarbonization of building space heating previously not thought possible.

Prior to Passive House, space heating reduction was not a priority in Massachusetts. Codes and popular rating systems like LEED targeted reductions in total building energy and were neutral as to what was improved or reduced (e.g. gas, electricity, lighting, heating, cooling, fans, envelope, etc. were all treated the same). Indeed, it was not uncommon for designs to increase space heating. This was happening because energy code allowed, for example, swapping reduced envelope performance for improved lighting performance. Code was satisfied so long as total energy use was reduced.

Further, for many Massachusetts commercial building types, space heating makes up only a small part of total building energy use. In office buildings, for example, space heating makes up less than 10% of the total energy use [Zimin 2022]. Because total energy reduction is the goal, there was little reason to go to extraordinary lengths to reduce something which makes up only a small part of the total.

Then, toward the mid-2010’s two significant trends converged which elevated the importance of space heating reduction. First, Massachusetts was on its way to a renewable electric grid with near 100% generation from wind, solar, and hydroelectric. [Massachusetts 2022]. Second, by the mid 2010’s, “cold climate” air source heat pumps had become available in Massachusetts [NEEP, 2024]. These devices enabled, for the first time, an affordable and feasible swap from fossil fuel to electric heat pump heating despite Massachusetts’ cold winters [Johnson, 2013].

The convergence of these two trends provided an opportunity to ubiquitously electrify, and thus decarbonize, building space heating which was previously unattainable. In 2024, electric grid emissions rates are such that space heating with electric heat pumps has less than half the emissions of on-site fossil fuel combustion. By 2050, once renewables are fully in place, space heating with electric heat pumps will have 95% less emissions [Ormond 2022].

However, a fossil fuel to electric swap without significantly reducing the space heating demand itself first would introduce a large new, very costly, peak load on the electric grid. By the early to mid 2010’s, it become clear that heating load reduction would be crucial to facilitate a grid friendly fossil fuel to electric swap.

Fortunately, at about the same time (mid-2010’s), large, commercial-scale Passive House projects began to be built in the Unites States. What was most notable about these projects was that they demonstrated that it is possible to reduce space heating to such an extent that a swap from gas to electric space heating can be made without necessarily resulting in large new peak electric loads, and in some building types, it’s even possible to have no increase in electric peak loads [Zimin 2022]. Passive House challenged the “conventional wisdom” that a gas to electric transition would require massive electric grid upgrades and costs.

The heat-crushing performance of Passive House, which solved the gas to electric grid concerns, was hard to ignore and the DOER, Massachusetts’ utilities, and the Massachusetts Clean Energy Center (MCEC) began to seriously look at whether and how Passive House could be adopted in Massachusetts. Passive House comfort and resilience benefits were also hard to ignore. Its cost effectiveness soon became clear, as well, as described in Part 3.

Passive House had been an optional energy code pathway since 2012. However, few developers availed themselves of this pathway for many years. Massachusetts first Passive House (a single family) was not built until 2011. Little was known about Passive House in the local industry, a void which was quickly filled by fear of costs and risk. Perhaps the biggest misconceptions at this time keeping Passive House being “taken seriously” was the notion that Passive House was for small, single family homes only and that cost premiums were in the 15% range as compared to standard construction.

Then, in 2015 the Pennsylvania Housing Finance Authority (PHFA) introduced Passive House into their competitive selection process for multifamily developments. Developers responded rapidly. In 2015 and 2016, 18 winning projects, about 20% of all winning projects, were Passive House. Cost was also notable. In 2015, PHFA Passive House buildings cost just 2% more than conventional buildings. In 2016, Passive House buildings cost the same as conventional [Semke 2020]. This experience alleviated fears about construction costs and rapid adoption.

In 2016, a second Massachusetts Passive House building generated significant interest, being the first multifamily. This building had a profound impact on the Massachusetts design and development community. Taking a tour of the 110,000-sf “Distillery” project in Boston became a rite of passage for many in the development community seeking way to decarbonize and improve comfort and resilience. Energy performance for the Distillery, once complete and occupied, did crush heating demand, proving wrong the Massachusetts sceptics jaded by poor energy performance of some LEED certified buildings. The 2020 energy reporting data shows the Distillery with 60% lower energy use (and its associated utility costs) as compared to other non-Passive House multifamilies built to the LEED standard [Simmons 2022].

In 2016 and 2017, projects in New York City and Boston demonstrated that downtown high rises can be built to Passive House standards. In New York City, the 26-story, 352-unit, 272,000-sf “House at Cornell Tech” apartment building was completed in 2017. In Boston, the 53-story, 812,000-sf Winthrop Center began in 2016 (completed in 2023).

In 2017, the Massachusetts Clean Energy Center (MCEC), launched the Passive House Design Challenge, offering an incentive of $4,000/dwelling unit for affordable housing developers to build to Passive House to help jump start Passive House in Massachusetts and better assess Passive House costs. Eight buildings were accepted into the program, ranging in size from about 50,000-st to 150,000-sf. Average construction cost increase to achieve Passive House standard over required code was under 3% [Simmons 2022].

In 2019, Massachusetts’ utilities launched a statewide Passive House incentive, providing $3,000 per unit for residential buildings with 5 or more units. This incentive was launched in conjunction with funding for design professional and contractor training. This incentive was funded by Massachusetts’ nation-leading energy efficiency program MassSave®. Uptake of the incentive was significant. By 2023, completed Passive House certified buildings reached over 1 million square feet in 30 buildings with another 160 buildings with over 13,000 dwelling units underway [Craig 2024]. This dramatic uptake was occurring prior to any Passive House mandate in the energy code. Passive House at this point was still entirely optional.

During this time, the community of citizen-advocates mobilized by the GCA were taking note of Passive House’s rapid adoption and cost-effectiveness. Local training and advocacy groups like Passive House Massachusetts and Built Environment Plus emerged during this time.

With the 2021 passage of the NGRA the DOER was tasked with updating the Stretch Code and creating a new Specialized Code. In both codes, the DOER set out as a key objective “crushing” heating loads as much as possible to facilitate a grid-friendly fossil fuel to electric heat swap. This strategy also has the additional benefit of improved life cycle cost, resilience, durability, and comfort.

In both the Stretch Code and Specialized Code, the traditional approach of focusing on total building energy was entirely replaced with an approach that focused on limiting heating and cooling demand like is done in Passive House. In Massachusetts code, these are called the heating and cooling “thermal energy demand intensity” (TEDI) limits which are the equivalent to “space heating demand” and “space cooling demand” in Passive House.

The Stretch Code and Specialized Code also include entirely new provisions for thermal bridge accounting, credit for thermal breaks, high levels of ventilation energy recovery effectiveness, and strong air infiltration limits and testing which are either poorly addressed, or entirely ignored, by national model codes.

Although the Stretch Code itself does not include a Passive House mandate, the TEDI limits and the new thermal bridge, energy recovery, etc. provisions, which replace the old practice of simply reducing total energy performance, has the effect of orienting and focusing the building design industry toward addressing thermal demands like is done with Passive House, closing the gap between Stretch Code and Passive House. Because of the Stretch Code’s wide adoption in Massachusetts (85% of all municipalities), therefore, thermal-oriented design and attention to thermal bridges, ventilation energy recovery, etc. are now near universally required in Massachusetts.

Like the Stretch Code 15 years ago, the optionality of the Specialized Code offered an opportunity to introduce more ambitious provisions and inclusion of a Passive House mandate rose to the top as a high priority. At the time of Specialized Code development, Passive House had already achieved considerable momentum within Massachusetts: there were about 2,000 Passive House dwelling units already voluntarily underway in Massachusetts, well documented cost effectiveness, a state-wide $3,000/unit incentive from the utilities, and completed Passive House projects of all shapes and sizes across Massachusetts.

Perhaps most importantly, though, there were thousands of GCA-mobilized citizen-advocates, who, having at this point many years of experience in building issues, had deep appreciation for how effective Passive House was at space heating reduction, decarbonization, and enabling a grid-friendly gas to electric heating transition. These citizen-advocates mobilized during the Specialized Code development process and provided a critical voice in getting a proposed Passive House mandate across the finish line into the Specialized Code. These same citizen-advocates are now working locally within their municipalities across Massachusetts to upgrade their municipalities into the Specialized Code.

[DOER 2022] Department of Energy Resources, ‘Massachusetts Commercial Stretch Energy Code and Municipal Opt-in Specialized Code’, Regulation 225 CMR 23.00, 2022.

[DOER 2024] Department of Energy Resources, ‘Massachusetts Building Energy Code Adoption by Municipality’, available at https://www.mass.gov/doc/building-energy-code-adoption-by-municipality/download, accessed: 27 January 2024

[Craig 2024] Craig, B.: ‘Number of Housing Units Enrolled in MassSave Passivehouse Multifamily Incentive’ Spreadsheet, Massachusetts Clean Energy Center, accessed: 24 January 2024.

[Simmons 2022] Simmons, K., Craig B., McNeally L., Lino J.; ‘Scaling Up Passive House Multifamily: The Massachusetts Story’, Summer Study on Energy Efficiency in Buildings, 2022

[Massachusetts 2008] Commonwealth of Massachusetts, ‘An Act Relative to Green Communities’, Chapter 169, 2008.

[Massachusetts 2021] Commonwealth of Massachusetts, ‘An Act Creating a Next-Generation Roadmap for Massachusetts Climate Policy’, Chapter 8, 2021.

[Zimin 2022] Zimin, P., Arena L., Lavu N., Martello, D., Moore, S., Hudson M., ‘Building Energy Study to Inform the Development of 2023 Commercial Energy Stretch Code’, Department of Energy Resources, Appendic C, 2022.

[Massachusetts 2022] Commonwealth of Massachusetts, ‘Clean Energy Climate Plan for 2050’, December 2022.

[NEEP 2024] Northeast Energy Efficiency Partnership, ‘Heat Pump List’, available at https://ashp.neep.org/#!/, accessed: 27 January 2024.

[Johnson 2013] Johnson, R., ‘Measured Performance of a Low Temperature Air Source Heat Pump’, United State Department of Energy, Building Technologies Office, September 2013.

[Ormond 2022] Ormond, P., Zimin, P., “Stretch Code, it’s Electrifying”, BuildingEnergy Boston, Northeast Sustainable Energy Association, March 2022.

[Semke 2020] Semke, Z., ‘Low Income Housing Credit: A Sleeper PH Catalyst’, Passive House Accelerator, February 2020, available at https://passivehouseaccelerator.com/articles/low-income-housing-tax-credits-the-sleeper-passive-house-catalyst, accessed 27 January 2024.

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