Passive House Helping Shape State Energy Codes

British Columbia has been the advance guard in North America when it comes to progressive building energy codes, with its BC Energy Step Code whose Step 5 performance levels closely resemble Passive House targets. More recently, Passive House performance levels have been showing up in U.S. state energy codes from coast to coast—or at least in Massachusetts and Washington. The shift may not yet be an overwhelming groundswell, but it’s a welcome development.

In Massachusetts, the Department of Energy and Resources (DOER) last December released its updated energy code, which is part of the forthcoming 10th edition of the Massachusetts building code. The updated code includes a revised stretch energy code, as well as a second, more advanced tier of the stretch energy code known as the Specialized Opt-in code. Both of these codes include new building enclosure requirements that are quite familiar to Passive House practitioners, such as stipulations regarding air tightness and accurate accounting of thermal performance of assemblies, including glazing systems. The Specialized code goes a step further and requires Passive House certification for multifamily housing over 12,000 square feet.

“To date, 299 of 351 municipalities were already following the previous stretch code in Massachusetts, and as of July 1, 2023, have rolled into the updated stretch energy code. Towns that vote to adopt the new Specialized code will be held to the requirements of that more advanced tier,” says Andrew Steingiser, an associate senior project architect and Passive House consultant at RDH Building Science’s Boston office. RDH was invited to join the DOER’s Stretch Energy Code Technical Advisory Committee, and Steingiser has been serving as RDH’s representative.

“I know through conversations with some of the folks at DOER here that they were looking at Vancouver's model when designing this second, more advanced tier stretch code,” notes Steingiser, adding, “There's a lot of parallels between Vancouver and Boston right now.”

One such parallel is the development of new multifamily buildings that are aiming for Passive House performance in the greater Boston area—not surprising, given these new codes, combined with the generous incentives offered through Mass Save. According to Mass Save, 119 multifamily buildings, with more than 6,700 units, are on track for Passive House certification by 2026.

Schools are another building type whose designers may as well familiarize themselves with Passive House methods. The new requirements for this typology follow a thermal energy demand intensity (TEDI) pathway that can be quite rigorous. The TEDI energy modeling guidelines are new and specific to Massachusetts, so the modeling is not exactly like that done for Passive House, but is influenced by many of the same elements.

One recent school project that Steingiser was consulting on had a heating TEDI requirement of 2.2 kBtu/ft2/yr—or about half of PHI’s heating demand target. “The TEDI requirements are a minimum requirement for some of these program types in the code, but Passive House remains a code compliance option for all building types, so in this scenario, you could choose to pursue Passive House instead,” explains Steingiser.  Whether pursuing the Passive House or TEDI compliance pathway, the methods used to achieve the standard overlap significantly: careful attention to the building enclosure detailing with regards to airtightness, adequate R-value, minimizing thermal bridging, the form factor of the building, and percentage glazing, along with heat-or energy-recovery ventilation and optimized mechanical systems.

Across the continent Dave Fox, senior project manager at RDH Building Science’s Seattle office, is seeing some exciting code developments moving Washington in the Passive House direction, even though the trajectory is not as clear cut as it is in British Columbia. Since January 2020, the state energy code has included a Passive House compliance pathway for single-family residential buildings, but that hasn’t been extended yet to other typologies.

“Washington State and the City of Seattle have focused their efforts to combat air leakage, aiming for more airtight buildings,” Fox says. Until recently airtight assemblies were included in the code, but there was no actual airtightness target requirement that had to be met. “The upcoming building code will be more involved. It will require builders to return to existing buildings and rectify any air leakage issues to meet the specific targets.” he explains. The target for the new code is 0.25 CFM50/ft2, so it is not as stringent as Passive House, but it is a step in the right direction.

“Our code is also tightening the screws on the efficiency of all our assemblies, so, for example, the window requirements are going to get a little bit tighter in this next code cycle along with more serious requirements for thermal bridging,” Fox points out. “It's not as aggressive as say, B.C. [British Columbia], where they’re more rigorous about the detail modeling of window assemblies,” he continues, noting that, “We're just not quite there yet, but hopefully we'll move in that direction soon.”

Another step that Fox regards as a positive move is the state’s rules regarding heat pumps for heating and domestic hot water in commercial and large multifamily buildings; at press time the details for these rules were still being hammered out. “I'm really excited for it. I think it's a great step in decarbonizing our heating loads,” he enthuses.

New York State and the City of Denver also have Passive House compliance pathways for specific building types. With all of these code examples to follow, other jurisdictions could be copying this trend with relative ease.

For a fuller discussion of these building code changes, listen to Zack Semke’s talks with Dave Fox and Andrew Steingiser on the Passive House Podcast.

Top image: The Madrone Apartments, Seattle WA, rendering courtesy of Cascade Built.