Rise | We've Done the Research
Bowers began the home-building process with a floor plan that he modeled in PHPP (Passive House Planning Package), an Excel spreadsheet developed by the PassivHaus Institute. "After each iteration, I updated the model to optimize things like wall thickness, window area, and overhangs," he says. After figuring out the home's final square footage and volume, Bowers "optimized the wall thickness to meet the PassivHaus standard.
How Was the Rochester PassivHaus Optimized for Efficiency?
The house was built using 16" double-wall construction with 2 x 2x4 walls spaced seven inches apart." The 16-inch double-wall assembly is insulated with dense-packed cellulose, achieving an R-55. The interior load-bearing 2x4 wall is a service cavity. The carefully sealed ZIP system on the exterior side of the interior wall is the air barrier layer. A 1.5-inch rain-screen gap and a weather-resistant barrier layer on the double-wall assembly's exterior side prevent moisture from entering the wall.
Bowers, his wife, and their children moved into their 2,900-square-foot, farmhouse-style home in 2016. "We spend about $210 a year to heat the house," he adds. "Our average electric bill is about $88 a month. We retain the heat through a lot of insulation and super air-tightness."
PassivHaus Energy Efficiency
The family doesn't use or need solar to power the all-electric house. PassivHaus construction ensures super energy efficiency. Also, because "we open up the house to tours, we don't want people to think our low utility bills are because of solar power," Bowers says.
Bowers engages in extensive energy monitoring "as it's a major selling point when I'm reaching out to new clients." He regularly fields questions about the utility bills, as well as how much his upfront costs were.
"We spent about $32,000 more on our PassivHaus house than a code-built house would cost, but we have the same mortgage payment," Bowers says. "I figured that out by modeling how much we'd spend on propane, which a traditional home would have needed to use given our location," he explains, "then did the same model for our PassivHaus, and figured out how it would translate into savings over a 30-year mortgage."
An ERV (energy recovery ventilation system) exchanges the air in the house once every three hours. Inside the house, the family used no- and low-VOC paints and finishes, hardwood cabinets, and resilient flooring "because of the four kids and a dog," Bowers says. The family has ENERGY STAR appliances and a heat-pump clothes dryer.
A CT on the ventilation system "quantifies the cost of fresh air," Bowers says. "Surprisingly, we spend more money on new filters than we do in electric to run the machine." Because he considers the heat-pump dryer and induction/convection stove "energy hogs," Bowers measures their use, as well.
"On top of these devices," he continues, "I am monitoring the indoor air quality in the house, which helps me to identify how cooking, parties, even vacuuming impact our air quality. It's also a good reminder to change the filters in the ERV when air quality starts to dip for longer periods."
He measures temperature, humidity, total VOCs, particulate matter smaller than 10 microns (PM10) and 2.5 microns (PM2.5) with a RESET Air Certified Tongdy Unit. He also has a UHOO IAQ monitor, which is less expensive than the Tongdy, "but doesn't have any published accuracies or calibration requirements, so I'm not exactly sure how accurate it is." As such, "it's good to have the control monitor with the Tongdy."
Lessons Learned
Bowers says that during construction, installation of the ventilation system necessitated drilling many 3.5-inch holes in the joists between the first and second floors. "If would have known, I would have done an open-web truss instead," he says.
While the family enjoys the cooling provided by the two wall-mounted mini-splits, Bowers wishes he would have come up with a way to improve the cooling distribution upstairs. In the winter, we don't need to turn on the second-floor heat pump. But cooling the upstairs in the summer is a challenge as the mini-split is un-ducted."
He suggests that homeowners intending to build a Passive House should collaborate with their architect and Passive House consultant from the get-go. The Bowers family worked with Grater Architects, a firm with LEED-accredited professionals, "and because of partnership, it was pretty easy to coordinate changes and how those changes affected performance.
During the design process, "window sizes, overhangs, and window locations change constantly," he adds, "with serious consequences in the performance of a home. So, it's beneficial to have the designer or architect understand how changes can affect the energy model."
While Bowers finds the engineering in PassivHaus construction "fascinating." He's also glad the home's construction and operation result in minimal environmental impact.
But, the biggest selling point for us is comfort.
Camille LeFevre
Camille LeFevre is an architecture and design writer based in the Twin Cities.
