Passive House principles put to work in this Portland home reduce heating needs by 90% compared to a typical home of the same size.
“I think of the design process as a tripod, with form, function, and budget comprising the three legs,” says homeowner Mark Darienzo. “For us, function and budget determined the form.”
He and his wife Robin Cash bought a “tear down”—a neglected foreclosed house in northeast Portland—and Darienzo deconstructed most of the house himself, carefully setting aside materials that could be recycled or repurposed. For home-building ideas, the couple attended solar tours in Portland and Bend, Oregon, and after interviewing several architects, hired Portland-based building company Green Hammer to complete the design.
“The budget was extremely tight for a custom design/build,” says Stephen Aiguier of Green Hammer. The resulting contemporary saltbox design slashed in half the home’s original square footage. The 1,327-square-foot floor plan includes a handicapped-accessible bathroom and home office downstairs.
Green Hammer’s Alex Boetzel persuaded the couple to build a house that met Passive House standards, which means an airtight structure that reduces heating needs by 90% compared to a conventionally built home of the same size. Green Hammer achieved this in part by isolating the concrete slab from the foundation with rigid foam board insulation. Attaching a BCI “curtain wall” to the exterior of two-by-four stud framing resulted in 14-inch-thick walls, which were filled with dense-packed cellulose insulation. Triple-pane, fiberglass, argon-filled Cascadia windows helped complete the very tight envelope, and a concrete slab and double layers of interior drywall added thermal mass inside.
Water conservation was another priority. The couple’s rainwater harvesting system features a 3,000-gallon cistern, pump, and series of filters, including a UV filter. They have a municipal hookup but haven’t yet dipped into city water, though that could change once landscaping is in place.
A Passive House’s primary energy demand—for heating, domestic hot water, ventilation, and electric appliances—cannot exceed a yearly threshold of 120 kWh per square meter of living area. The Cash-Darienzo home’s primary energy was estimated at 114 kWh per square meter. Because the pump and UV treatment unit uses so much of their allotted energy budget, Cash and Darienzo chose to sacrifice another big energy user: a clothes dryer. Instead, they line-dry clothes outside or in the bathroom. A 3.29 kW grid-tied PV system leased from SunRun offsets a portion of their annual electricity use.
Boetzel determined that the small roof area and modest demand for hot water didn’t justify a solar thermal system. Instead, a waste-heat recovery pipe draining from the upstairs shower preheats incoming cold water, reducing water-heating energy consumption.
The couple’s house was featured on two tours in 2012: Solar Oregon’s Goal Net Zero tour in June, and the City of Portland’s Build it Green! tour in September. The home was also the site of drop-in workshops on rainwater collection and Passive House design.