Although the project could have reached certification-level performance with double-glazed windows, the vendor can only produce pre-certified Passive House windows that are triple glazed. “Because we’d selected these windows primarily for their innovative wooden frames, and they were made in North America, we were unwilling to upset the project schedule by doubling back on this decision,” Barry says. On the metal siding, a cost estimate is underway to see if cement-board siding is a desirable alternative.
Another consideration was whether to pursue PH Plus certification—the original intent—or remain content with PH Classic, thereby eliminating the need to buy additional PV panels. The purchase of additional PV to reach PH Plus is a complex issue. “We need to consider how clean the utility-provided power is here and the likely carbon footprint of either option,” notes Nicely. But it does at least raise the discussion of whether going for a higher level of certification is always the right choice.
An open house similar in design and purpose to the one at the Sky Ranch property, will be held at 17 Mile Haus in April 2023. Hopefully, it will convince even more potential clients and public officials of the benefits that Passive House brings to California communities.
- Melanie Bretz
Embodied Carbon Gets Real
It was somewhat alarming to run the first of my own designs through Passive House Network’s PHribbon plug-in, which I did with assistance from Passive House certifier Steve Mann. The process was at turns uncomfortable and validating. While we found that PHribbon was able to answer many questions, it became apparent that most carbon analysis tools—including PHribbon—remain limited. For this reason, I cautioned our team against drawing any solid conclusions beyond the glaringly obvious choices Rob Nicely discussed. Here are a few of the variables that we know could change our results quite dramatically:
■ Code Comparison: Our code version here assumes a mixed-fuel HVAC system. It also assumes an airtightness of 3 ACH50, double-glazed windows, and extract-only ventilation. We could make this scenario look a whole lot better by making it all electric, or much worse if we used spray foam insulation instead of cellulose. We kept it mixed fuel to illustrate a point.
■ Grid Decarbonization: The timeline for the grid to become fully decarbonized (fed by 100% renewables) is unknown. PHribbon allows us to toggle this variable to see how it impacts our choices regarding installation of PV and battery storage, making it a highly complex decision, and beyond the scope of our analysis and this discussion.
■ Limited EPDs: The availability of Embodied Product Declarations (EPDs) that PHribbon sources from EC3 is robust, but incomplete. Not all manufacturers have submitted EPDs. This means that results are approximations, and we cannot claim exact embodied carbon metrics yet.
■ No Targets: PHribbon currently references the 2030 Embodied CO2 targets set by the Royal Institute of British Architects (RIBA). A similar target for U.S. embodied carbon is not yet available. Compared to the RIBA 2030 residential building benchmark of 58 kgCO2e/ft², our 34.3 kgCO2e/ft² looks exceptionally good, but may not stand up as well when compared to a local target (TBD).
■ Variability: We realized that our results represent a snapshot in time. All results will change in the future because the production footprint of many products—including PV and glass—will likely drop as various grids decarbonize. What will remain is the ability of this building to be habitable and best able to support a 100% renewable grid. See this ACEEE study comparing two near-Passive House homes with five Net Zero Energy homes in California, to validate this point.
- Bronwyn Barry
All Electric Passive House Tour
Since our first opportunity to do a certified Passive House project in 2011, we have always tried to leverage opportunities to raise awareness about the extreme energy efficiency associated with Passive House building practices. At the Sky Ranch Project, when the shell was complete and before the interior walls were covered, we set up 13 stations that each demonstrated a key principle of Passive House design and building. We also created a virtual tour that resides on our website. We identified around 400 people to invite, including general contractors and various subcontractors, architects and engineers, and all manner of people from the community who either had an interest in sustainability or whose job was related to setting or implementing policy around climate change. These invitees included city council members, building and planning officials, and city managers of the 17 cities in our area, as well as the boards of supervisors in Monterey, Santa Cruz, and San Benito counties, and leaders and supporters of climate change activism. We invited our Senator, Congressional Representative—who did visit the project—and California’s Governor. I even went so far as to write an action plan for our region stating the goal of 1,000 Passive House buildings in our region by 2030 and sent it to everyone we invited. The open house was well-staged with posters and demonstrations of the concepts and systems. We held education sessions for leaders from a variety of organizations at the house as well.
- Rob Nicely
