As a Passive House consultant, Salt Lake City architect Dave Brach, AIA, knows what it takes to meet the program’s stringent energy-efficiency standards, and the Ruby House site didn’t look especially promising. “It was just a little slice of lot,” Brach says of the space in his city’s Avenues Historic District. Its long side faced west, not the ideal solar orientation, and, to further complicate matters, being in a historic district made the project subject to architectural review. But clients Darcy and Brandon Wolsey told Brach to give it his best shot. “And that’s what it takes,” Brach says, “putting it on the agenda right from the outset.” That commitment yielded not only a Passive House certification, but also a house that is comfortable, inexpensive to operate, and an asset to the neighborhood as well as its owners.
The Historic Landmark Commission was flexible regarding style, Brach says. “But we had to draw the street façade on both sides to show them how the house would fit in,” he adds. The neighboring Victorians and bungalows are sided in wood, stucco, or brick, so he developed Ruby House’s street elevation as a three-part harmony of stained Accoya (a sustainably sourced, nontoxic, treated softwood), stucco, and thin veneer brick. “We wanted to maintain a nice rhythm,” Brach says, so the building’s three volumes recede from the street in a stepwise fashion. Dark fascias and matching aluminum-clad Energate windows, which are triple-glazed with unit R-values of 6.1 to 7, crisply delineate the building forms.
Brach applied the exterior wall finishes over a 2-inch layer of expanded polystyrene that encloses the building’s double-stud exterior walls, which are filled with 12 inches of high-density fiberglass insulation (assembly R-values: 37.6 to 42.9). The roof consists of 9.5-inch engineered rafters overlaid with sheathing, structural insulated panels, and reflective membrane roofing (assembly R-value: 58.8). “We framed the whole house as a box and did our airtight layer—a fluid-applied film—on top of that,” Brach says. “To generate the eaves, we laid 4.5-inch SIPs on top and furred them down to the right thickness.” Below-grade spaces are contained within an insulating concrete form foundation furred out with a 2x4 interior wall that is insulated with high-density blown fiberglass (assembly R-value: 35.3). Twelve inches of EPS foam insulation under the slab give the lower-level floor an R-value of 44.5.
Given the efficiency of the shell, Brach says, “the building doesn’t require a lot of winter solar gain, but it’s still part of the equation.” South-facing windows harvest winter rays and also “animate the façade and make it a good neighbor.” Overhanging eaves protect the upper-level windows from the summer sun, while a wooden awning shades the living room windows on the first floor. A retractable fabric porch roof solves what Brach calls “that classic dilemma”: the choice between a too-sunny porch and a too-shady interior. A similar device shelters the back garden, between the house and its detached garage. “It’s a little covered dining space,” Brach says. “You couldn’t sit out there in July and August without shade.”
Brach devoted special attention to locating windows for summer ventilation and to minimizing unwanted heat gain. “On the upper level, we have operable windows at the south, north, and west sides,” he says. “We tried to get a fair amount of nighttime flushing.” A long west-facing window in the dining area required movable shades, which caused some consternation. “You want shades to be on the outside; that’s ideal,” Brach says. “But cost became an issue.” The alternative—interior roller shades that retract into a wall pocket, taking up precious insulation space—forced him to revise his energy model. Fortunately, he says, “I had built in a little cushion,” and the heat-loss number remained within the Passive House target range.
The effort produced a building shell with peak heating and cooling loads of only 9,000 Btu per hour and 12,000 Btu per hour, respectively, and a cascade of downstream cost savings. A pair of Fujitsu split-system air-source heat pumps—a 7,000-Btu unit upstairs and a 9,000-Btu unit downstairs, both rated at 19 SEER—provide heating and cooling. “The installed cost for those was less than $5,000,” Brach says. The low-load building envelope and efficient LED lighting hold monthly electric bills to an average of $50. Cooking and hot water are handled by gas appliances and a high-efficiency, sealed-combustion A.O. Smith water heater. A 93-percent-efficient Zehnder HRV system keeps indoor air fresh when the windows are closed.
The ultimate test of a home’s performance, however, is owner satisfaction, and Ruby House (named, incidentally, for the owners’ dog) scores high on that measure. Brandon Wolsey says that he and his wife appreciate the house’s low operating cost and exemplary environmental footprint, but they really love the quiet and competent way that it goes about its business. “It’s all pretty much on autopilot,” he says. “We set our heating and cooling, and we leave it alone. The temperature stays really stable throughout the living space. We don’t have radiant floors, but on a January morning you can walk around in your bare feet and be totally comfortable.”