by Andrew Steingiser
Architects must address many factors when designing a building. Just to name a few, there’s zoning, context, historical considerations, massing, program, accessibility, client needs, and cost. Let’s not forget conveying meaning through the design that acknowledges the canons of architectural theory and precedent – the interesting part. Then add the following to the mix: designing to address the climate crisis and keeping up with the shifting code landscape. That’s a lot to consider!
Architects who work in Massachusetts should be aware of recent changes to the Energy Code released in December 2022 by the Massachusetts Department of Energy Resources (DOER). As part of the updated 10th edition of the Massachusetts Building Code, the new base Energy Code includes updates to the Stretch Energy Code as well as the addition of a second, more advanced tier of the Stretch Energy Code known as the Specialized Opt-In Stretch Code. These code changes are based on the 2021 International Energy Conservation Code with Amendments. The 299 out of 351 municipalities in Massachusetts already enrolled in the current Stretch Energy Code will continue to follow the updated Stretch Energy Code. Towns that vote to adopt the new Specialized Opt-In Stretch Code will be held to the requirements of that code. The implementation of the more stringent requirements in both stretch codes will advance progress toward the Commonwealth’s 2030 and 2050 carbon emissions reduction targets for buildings, which were signed into law on March 26, 2021 by Governor Baker.
You should be aware of a few key changes in the updated Energy Code. First, the Stretch Code and the Specialized Opt-In Code include multiple new paths based on the size and program of your building. You will have to check the code to determine which compliance path your building falls under. Depending on the applicable path for your building, you may have more than one option for code compliance. The path you select will set the performance targets that your building is required to achieve. Passive House remains a code compliance option for all building types.
Most paths will require energy modeling to satisfy an absolute metric. Gone are the days of a single Stretch Code approach for all buildings over 100,000sf, as was the case under the 9th edition of the building code. The new Stretch Code and Specialized Opt-In Code apply to all buildings of all sizes, including additions and alterations. For many commercial and multifamily residential buildings, you will use the energy modeling process to determine the R-value and U-value requirements for the building enclosure.
The code updates still include an enclosure backstop calculation, but it is simplified from the previous 9th edition. In the paths requiring energy modeling such as TEDI or Passive House, the performance requirements resulting from the modeling for your selected path will likely exceed the minimum requirements of the backstop calculation and will determine your building’s enclosure requirements.
Across the board, the code updates place a greater emphasis on energy demand reduction measures, something that those of us in the Passive House community are well familiar with. A high-quality, airtight building enclosure with continuous control layers and the elimination of thermal bridging will allow for passive reduction of energy use in heating and cooling systems. Airtightness testing is now required to confirm the performance of air barriers in the building. The best way to ensure compliance with airtightness requirements is to develop a carefully coordinated set of enclosure details, particularly at transitions between assemblies, before a shovel even hits the ground. With an airtight building comes the need for ventilation rather than reliance on outside air infiltration. Heat recovery ventilation is required by code, which controls further energy loss through ventilation.
The Energy Code updates also emphasize making buildings all-electric to eliminate on-site combustion in buildings. This makes it even more critical to reduce the energy demand of buildings first to avoid overburdening the electrical grid. Additionally, building owners will not want to pay more on their energy bills as electricity rates continue to climb in Massachusetts. Speaking of all-electric, there is now a requirement for all-electric heating systems if you want to design an all-glass building. The energy modeling process will likely show that all glass is not going to be feasible anymore for most buildings. Sorry, my fellow black-spectacled friends!
All these changes in the Energy Code are creating a shift in the traditional design process. We can no longer design buildings however we like, then check their conformance with the Energy Code later before filing for a permit. Projects will benefit from an early-phase integrated design approach, where design teams think a little bit about everything starting on day one. Performance requirements will help inform and shape your designs from an early phase, and an energy-modeled process will be required to confirm the ongoing performance compliance of your buildings as they progress through the design process. You’ll need to pay careful attention to building enclosure detailing and mechanical system specifications earlier in the design process than you are used to. The performance of the enclosure and mechanical systems are explicitly linked and are primary elements that require careful attention to achieve energy targets.
While this may seem like a lot to take on, these new code requirements will start us down a path toward future-proofing our buildings. The upcoming penalties from programs like BERDO represent the closest thing we have in the U.S. to a carbon tax and will only continue to gain prominence. Also, what is the expected life span of our buildings? What future climates will our buildings need to shelter us from? By acting now, we can avoid the levies of the future.
The following summaries can help you become familiar with terminology pertaining to the new Energy Code compliance paths:
HERS: The Home Energy Rating System was originally developed for single-family residential houses and adapted for small multifamily projects. Based on an energy modeling process by HERS Raters specific to this system, buildings achieve a score on a scale. The updated Stretch Code and Opt-In Stretch Code use HERS scores mostly for smaller, low-rise residential buildings, including some multifamily buildings, where Passive House is not explicitly required.
TEDI: The Thermal Energy Demand Intensity is an absolute metric that measures the annual heating or cooling energy demand, in other words the amount of heat that is delivered or removed by all heating or cooling equipment. It uses the same units as Energy Use Intensity: kBTU/sf/yr. The Energy Code lists the required values for both heating and cooling TEDIs by the size and program of the building. This metric targets the heating and cooling to align with passive design philosophy, reducing the loads to minimize energy consumption. Particularly with heating, fossil fuel sources are often being used, which means the operational carbon emissions for this energy use can be quite intense. TEDI relies primarily on building enclosure and ventilation system performance. In some cases, the annual heating limit through this TEDI path is actually lower and more stringent than the annual heating limits for the Passive House path. This path is evaluated through hourly energy modeling, such as eQuest and EnergyPlus.
Passive House: This design standard is based on absolute metrics that are focused on thermal comfort and significantly reduced heating and overall energy consumption. Achieving the Passive House standard requires significant attention to detail with respect to the enclosure, ventilation, and heating/cooling systems. Passive House requires that the project passes a strict maximum air leakage test at completion before certification can be achieved. It is a clearly defined standard that has been around for nearly 30 years and is well-suited to multifamily housing in cold climates. It includes all the demand reduction measures that the new Energy Code now requires. This path is evaluated through proprietary energy modeling software specific to these standards by Certified Passive House Consultants.
ASHRAE 90.1 Performance Energy Index (PEI): This metric began as the Performance Cost Index in ASHRAE 2016. The Stretch Codes reference ASHRAE 90.1 2019 and amend this metric to reflect energy rather than cost. The PEI takes into account building performance relative to the climate zone, and specific targets are set in the Massachusetts amendments per a list of different building program types. This metric replaces the previous ASHRAE 90.1 Appendix G-based Stretch Code approach that required performance 10% better than a baseline building. This path is evaluated through hourly energy modeling, such as eQuest and EnergyPlus.
Andrew Steingiser, RA, CPHC, LEED AP is associate, project architect, and Passive House consultant at RDH Building Science.