Navigating through Passive House, LEED, and Minergie-P-ECO territory.
I had the pleasure of speaking recently with Cory Hawbecker, designer at Holst Architecture, about the Karuna House and its certifications. We’re building the project to Passive House, Minergie-P-ECO, and LEED for Homes Platinum standards, and Cory is playing a lead role in navigating the project through the myriad of requirements. It’s a pretty unique task, perhaps the first time it’s ever been done.
“The client for the Karuna House wants to create a beautiful sustainable home that he can enjoy, of course. But he also sees the project as a learning tool for the building community,” Cory said. “The question we’re exploring is, ‘How do the green building certifications compare and how do they contrast?’ We hope that the lessons we learn will be helpful to designers and builders across the country.”
Here’s what we’ve discovered so far …
What’s special about Passive House – a singular focus on performance.
The Passive House standard focuses entirely on building performance. It’s simple, and it doesn’t care how you achieve the performance. If your project achieves the required benchmarks for airtightness, energy demand and ventilation, then it’s certified. Period. The result of this singular focus? The Passive House standard achieves extraordinary energy performance gains. And the Passive House Planning Package’s modeling results correlate closely with real world performance once built, so the Passive House standard provides significant certainty that promised performance gains will be realized.
But this singular focus on building performance opens the standard to critique from those who ask, “What about the embodied energy of materials? Or toxicity of materials? Or location of site? Or access to transit? Or use of native plants?”
It’s true that these broader sustainability questions are not addressed by the standard. Passive House practitioners counter in two ways:
- First, the most pressing problem that we need to address in our buildings is their contribution to global climate change. After all, well over 40% of US greenhouse gas emissions come from the building sector. So Passive House’s intensive focus on building energy performance makes sense.
- Second, while the standard intentionally ignores broader questions of sustainability, Passive House designers and builders themselves do address them as they develop a project. Those efforts just aren’t recognized by the Passive House standard itself.
Still, there’s no question that Passive House doesn’t consider broader sustainability questions. It’s intentional: a singular focus on performance.
What’s special about LEED – a broad spectrum of sustainability.
LEED, on the other hand, doesn’t focus its attention in one area but instead works to address a broad spectrum of sustainable design and construction concerns. In many ways it’s the complementary opposite of Passive House. And while some elements of the standard are performance-based, much of it is comprised of prescriptive elements, grouped into a comprehensive system of checklists that address things like embodied energy, toxicity, site selection, access to transit, use of native plants, and much more.
But LEED’s broad scope opens the standard to critique from those who ask, “What about energy performance? How can you call a building “Platinum” if its energy use is only marginally better than a similar building built to code?” Historically, LEED buildings have fallen short in reducing energy consumption.
Proponents of LEED will say that the US Green Building Council (the body that created and oversees LEED) is addressing this once-blind spot. Progress has been made recently, and there are even discussions about making Passive House the energy performance component of LEED, which could be very powerful.
But there’s no question that the effort to address a broad range of sustainability questions has made it more difficult, at least in the past, for LEED to focus effectively on building performance.
So what about Minergie-P-ECO? And what do the “P” and the “ECO” mean?
Chances are you haven’t heard of Minergie before. It’s a pretty recent Swiss import, and the Karuna House will be one of the first structures to gain Minergie certification in the US (if all goes well).
According to Cory, Minergie started in Switzerland as part of an effort to make energy efficient buildings accessible to a mass market, much like ENERGY STAR here in the US. Affordability is a prime component of the base level of Minergie, and energy performance is adequate, but hardly revolutionary.
However, when you add the “P” of Minergie-P, then you’ve got revolutionary energy performance. The “P” adds on a Passive House-like standard of building energy consumption. Some of the details of how Minergie-P is calculated are different from Passive House, but in the end the two standards are quite similar, both performance-based and both focused on big reductions in energy use.
The “ECO” is analogous to the broader sustainability concerns of LEED. It addresses things like site selection and embodied energy, but also adds a couple of unique foci, like limiting exposure of workers in the field to toxics, and safeguarding occupants’ experience of a building (going so far as to consider the noise of pipes in the walls).
In a sense, Minergie-P-ECO takes the complementary opposites of Passive House and LEED, revises them, and combines them into one comprehensive standard.
Lessons learned so far.
“While they do have different emphases, what we’re finding is that there’s a lot of alignment among the standards, which is good news,” Cory told me. “The energy performance of all three point in the same direction, though Passive House and Minergie-P exceed what LEED requires. And just as LEED is concerned with materials selection, so is Minergie-ECO.”
That’s not to say it’s easy to achieve Passive House, LEED Platinum and Minergie-P-ECO in one project. Here are a few challenges we’ve encountered in the early stages:
- Site selection. Because the Karuna House is being built on the client’s vineyard in Yamhill County, it’s penalized by LEED for being a green field and for not being part of an existing neighborhood. Fortunately, because the energy performance of the house is so advanced, the LEED credits gained in that category will offset the credits missed due to the home’s location.
- No site-applied spray foam. Minergie-ECO prohibits site-applied foam, even one component products because it can expose the installer to fire retardants and catalysts if proper safety equipment isn’t used. The initial design of the Karuna House incorporated spray foam insulation. We switched to high density cellulose insulation, which is not only non-toxic but also scores high marks for its low embodied energy and low global warming potential. Still, one-component spray foam is a handy gap filler and adhesive, (spray foam should never be relied on as an air-barrier in a Passivhaus), so Minergie-ECO’s prohibition on the stuff adds challenges. To fill gaps between materials we’re now using acrylic impregnated expanding foam tape, for instance. T ighter tolerances and precision cuts from our skilled carpenters also reduce the need for one-component foam.
- No treated lumber. This is a conflict between Minergie-ECO and state building code. Due to toxicity concerns, Minergie-ECO doesn’t allow treated lumber inside the air barrier of a building, and encourages builders to avoid it outside the air barrier as well. The typical code-compliant method of building structural walls involves laying down a pressure-treated wooden sill plate on top of the concrete foundation, creating a buffer that protects framing lumber from the moisture given off by the concrete. Without the plate, mold, rot, and bugs can wreak havoc on framing. Our Minergie-friendly workaround? Use a borate treated sill plate installed over a structural epdm gasket to separate the wood from the concrete.
- No hood exhaust, no dryer exhaust. Code requires hood exhaust units in kitchens, which takes warm inside air and dumps it outside. Because it’s a huge source of energy loss, neither Passive House nor Minergie-P allow this approach. The workaround is to locate the heat recovering ventilation (HRV) system for the building near the kitchen, and to use a recirculating fan with charcoal filter to remove grease from exhaust air before it reaches the HRV. Similarly, Passive House and Minergie-P preclude conventional dryer vents. Our solution at Karuna is to use a closed cycle heat pump clothes dryer.
We’re just at the first phases of construction, so new challenges and lessons are bound to come up. We’ll share them with you here as they arise. Thanks for reading!
– ZackBack to Field Notes