Passivhaus Comes To California, Shattering Stereotypes
Renderings by Tomasz Biernacki, Perchara Studios
TreeHugger has written Forget Energy Star and LEED, The Real Green Building Standard is Passivhaus.. Most of the ones we have shown are in cooler, more northern climates, and most are small and boxy.
Therefore it took some time to figure out the O'Neill House in Sonoma, California, by Jarrod Denton of Lail Design Group and built by Solar Knights. It is anything but small and boxy, but is every inch a Passivhaus.
click plan to enlarge
The house was originally two structures connected by a covered breezeway, which is now enclosed and contains the kitchen, creating a courtyard design. That creates a lot of surface area; most Passivhaus designs we have seen minimize the surface area as much as possible because it is expensive to insulate and seal. Windows are expensive too; usually they have to be imported from Europe because until recently, nobody made windows in America with a high enough R Value.
But in the end, when you look at a larger and less boxy design, whether it is California or Canada, the philosophy is the same: A serious load of insulation. Walls are R-21 and the ceilings are an extraordinary R-74. Even the floors are R-12 to R-20. In California!
adding more rigid insulation to exterior wall. image: solar knights
Result: the house uses 70% less energy than a conventional northern California home. And then there is the maximum air leakage permitted in a Passivhaus, about a tenth that of a conventional house. This requires careful detailing and very, very good construction quality.
It also means that you have to bring in a lot of fresh air, since these buildings don't leak. Most Passive houses have heat recovery ventilators, but in warmer climates Energy Recovery Ventilators are used, that work in the cooling season as well, exhausting heat instead of recovering it. Denton writes:
This is the primary system within the house which distributes fresh supply air through a maximum 6" diameter mechanical duct at low volumn. A return air duct collects from the laundry room, bathrooms, and kitchen which runs through the ERV and potential energy is captured before it is exhausted out.
A secondary source of heat is from three solar thermal collectors on the roof to heat water, which goes through a heat exchanger.
A tertiary source is a mini-split heat pump that is required under California law, but probably isn't even necessary.
The O'Neill House doesn't LOOK like a Passivhaus. It looks pretty normal. Denton likes it that way, and told the Napa Valley Register:
"The architecture is not compromised," Denton said of the passive house, stressing that "visually, it won't look any different than any other house." There will be less noise in a passive house because it is better insulated than other buildings, Denton points out. "Indoor air is healthier, with a lower particle count," he adds.
Denton also told me:
I am proud that we have not asked the owner to compromise her living standards. This will first and foremost be an outstanding quality home with well appointed finishes.
Passivhaus is all about energy, but the house has lots of other features that will qualify it for LEED, including FSC lumber, local and recycled materials, drought resistant landscaping and rainwater harvesting.
Building a passivhaus is a lot of work, and I suspect this renovation was pretty expensive; there doesn't seem to be much left of the original house. But in Europe, where they are much more common, they claim that there is only a 5% premium over a conventional custom house. Perhaps as the market expands, the prices will drop here as well.