Flagstaff Couple Works With Their Passive Solar Home To Optimize Performance

When Dave and Jan Carlile retired, they decided to trade the temperate rainforest climate of Juneau, Alaska, for the arid forested mountains of Flagstaff, Arizona. "We'd spent a lot of money on staying warm and dry," says Jan. "We were ready to turn the tables."

In their new Southwest location, they decided to build a "maintenance-reduced" house," says Dave. "We'd rather travel than spend lots of time maintaining a house." With their backgrounds in conservation and interest in efficient resource management, the couple also wanted a new home "that would reduce if not minimize the negative impact we have on the earth." A sustainable home, they realized, would also mean decreased utility costs.

Last, they want to age-in-place. So, the couple asked their architect, Aude Stang of Architectural Design Studio in Flagstaff, to design "an energy-efficient, passive-solar home for two people," Dave says. "We also have an attached accessory dwelling unit for friends and family, which could also rent out for extra income if necessary or could use to house healthcare support in our advancing age." On the main level of the two-story home, a guest bedroom and bathroom provide the couple with a future option for aging-in-place.

Five years ago, they moved into their 1,700-square-foot dream home, which is clad in stucco and corrugated rusted metal siding and has a standing rib metal roof. "We adhered to the northern-hemisphere fundamentals of passive solar design," Dave says. "We found a south-facing hillside lot with good solar and proper orientation."

"We remind each other, on a day-to-day basis, how well the house functions as a passive-solar home," Jan says. "While the design of our home is straightforward, it serves us and is exactly what we want."

How Did The House Achieve Optimal Passive Solar Design?

Designed for optimal passive-solar heat gain, the home's axis runs east-west, with most windows or glazing on the south to catch the incoming sun and heat the stained concrete floors (which function as thermal mass). On the east, north, and west, says Dave, the windows tend to be few and small.

The roof insulation is blown-in cellulose "and spray foam to get a better seal" for airtightness, Dave explains, resulting in R-50. The walls have blown-in cellulose for R-30. Under the home's four-inch slab, "which is our thermal mass," are two inches of rigid foam that also wraps around the entire structure for R-10 and no thermal bridging.

How Can Homeowners Use "Behavioral" Participation to Improve Passive Solar Gains?

"Our implementation of passive solar necessitates some active involvement," Dave explains. During cool weather mornings, the couple moves their few pieces of furniture out of the way to "maximize heat gain on our solar mass." In the evenings, the furniture goes back into place as the floor radiates warmth.

In the summer, the couple opens the windows downstairs and in the master bedroom upstairs "to get a chimney effect, that draws the cool night air in through the first level and up and out of the upstairs windows," Dave says. In the morning, they close the windows up and draw the blinds. Their architect also designed overhangs that, in the summer, minimize solar gain on the thermal mass.

"It's rare, in the summer, that the interior temperature goes above 75 degrees."

Dave added. "We have ceiling fans if we need them. The design and structure of the house and our behavior is sufficient to keep home comfortable."

A Mix of Electric and Gas 

The Carlile's have six 280-watt solar panels that generate 1.7 kilowatts of electricity, which powers most homes. The grid-tied system means low electricity bills throughout the year. "Our highest electric bill is in the winter, at about $35 per month," Dave says.

In addition to the lights throughout the home, the solar panels power the ductless heat-recovery ventilators (HRV), which provide one air exchange per hour. The solar array also powers supplemental warmth via a few electric baseboard heaters, including those in the accessory dwelling unit. However, if the couple needs to warm up the house, they use the gas fireplace. "In the winter, we turn it on for two or three hours first thing in the morning to take the chill off," Jan says.

The whole-house Navien on-demand hot water system, which is gas-powered, includes smart preheating technology that recognizes hot-water use patterns to provide hot water when needed.

Keeping Things Simple 

In finishing the interior, the Carlile's used materials that don't emit or off-gas. In the kitchen, they chose floating shelves instead of upper cabinets to minimize their use of wood. "We also focused on reducing our water consumption and reuse our greywater," Dave explains. "In the upstairs bath, during nonfreezing months, we flip a drain switch and route water from the bathroom shower and sink out onto the property." Of course, they use biodegradable soap.

In the kitchen, they don't have a dishwasher. Instead, they wash dishes by hand and dump the rinse water into their native-plant garden. "We don't have any other interest in watering," says Jan, who seeded the garden, "and the plantings are doing well." They also collect water off the roof for the ponderosa pines and other native plants in their yard, but the rains are few and far between in the arid climate.

The couple doesn't have a clothes dryer, either. They either hang their laundry outside or use a drying rack. While their lifestyle might sound rather old-school, Dave says, it suits the couple perfectly.

Looking Back: What Would They Have Done Differently? 

Because the home is air-tight, Dave says, he chose the un-ducted, wall-mounted heat recovery system. "The HRV comes in pairs, which oscillate between fresh-air intake and exhausting old air," he explains. The home has two pairs of the HRV system, which is fine for the couple. "But if there are more than two of us in the house, the CO2 levels rise. Our interior monitor or CO2 sensor tells us how much CO2 is in the air."

"I wish I'd gone over budget and installed a third pair to improve the interior ventilation," he adds.

Outside, the clay soil of the mesa expands when it's wet and contracts when it dries. During construction, the contractor dug out the clay soil under the house's foundation and replaced it with cinders (the area had significant volcanic activity prehistorically). "But we didn't dig out the patio area on the south side," Dave says, "and the slab has sunk. It could eventually crack."

On the whole, however, Jan adds, "We don't spend a lot of time saying we wish we would have done this or that. We're just so impressed with how well the house functions as a passive-solar home." While they have concerns about the home's resale value, as it has a single-car garage and is smaller than many homes in the area, it suits them just fine.

"We often pause and comment to each other about how well the house has worked out for us," says Dave. "It's extremely livable."

Article by:

Camille LeFevre

Camille LeFevre is an architecture and design writer based in the Twin Cities.