When architecture professor Corey Saft and his wife began brainstorming ways to create a protected play area for their two children on their property, building a wall seemed like the natural solution. But Saft recognized an opportunity to accomplish a few of his professional goals. The plan quickly evolved into a vehicle for architectural experiment: a second house that would test Passive House criteria for a hot, humid climate while providing the desired buffer from an adjacent street. The resulting project also established a cost-effective prototype for sustainable urban infill.
Long and thin, the new house bounds the street edge of the Saft's property opposite their existing house, creating a central courtyard for family recreation. The narrow 1/7-acre site dictated the new home’s 17-foot-wide-by-50-foot-long form and compact footprint—800 square feet. According to the Passive House Institute U.S., it is the first residence in the southern United States to have been certified under the Passive House standard.
Saft, LEED AP and associate professor at the University of Louisiana at Lafayette's School of Architecture and Design, became intrigued with Passive House standards while working on a LEED project in 2007. "It just made sense," he reasons. "It's a clear, clean, direct way of appraising a building based on energy consumption."
He knew that applying the criteria in a cooling-dominated climate rather than a heating climate—for which the standards originally were developed—would require some key differences. Consultations with Katrin Klingenberg, executive director at the Passive House Institute U.S., yielded strategies for adapting the standards to suit Louisiana's steamy climate.
"Down here it takes a little more energy outlay because you have to cool the structure first," Saft says. "You also have to think about the windows and shading a bit differently. Shading is very important here." Instead of capturing and retaining solar heat and warmth generated by occupants, appliances, and other mechanical systems, a Passive House in a hot, humid climate must counteract internally and externally generated heat and humidity through strategic shading, mechanical ventilation, and energy-using cooling systems.
While many of the materials selections and wall assembly details are different for a Passive House in a cooling climate, according to Klingenberg, the principles stay the same: reducing energy consumption by 90 percent by creating a tightly sealed, highly insulated building envelope that minimizes energy losses; capturing or blocking solar heat; and reducing mechanical heating and cooling loads.
Adapting Louisiana's camelback shotgun style to suit the project's program, Saft created an open and spacious main living area with an 18-foot-high ceiling and loft area. The only enclosed rooms are the bedrooms and bathrooms. Rather than dropping the roof in front of the traditional camel's hump of upstairs bedrooms, though, Saft simply continued the roofline to create the double-height space.
To achieve passive solar performance and minimize heat gains, the house is oriented to the south/southeast. A series of operable clerestories along the north side and a partial wall of windows along the lower level of the south side flood the interiors with light, allowing occupants to reserve the use of efficient LED and CFL lighting for night. Opening both sets of windows creates cross ventilation and a stack effect, helping to cool the interiors when the 1,200 BTU, 19 SEER mini-split air conditioning unit isn't needed.
An energy recovery ventilator assists in maintaining comfortable indoor temperatures, introduces fresh air, and provides kitchen and bathroom ventilation. The house also is equipped with ceiling fans in each bedroom and in the living area.
The house's 24-inch on-center advanced framing system uses a combination of 2x6 studs on the bottom half and 2x8 studs throughout the double-height space. In designing the wall assembly and cladding system, Saft and Klingenberg carefully considered the local climate. In addition to R-55 open-cell spray foam insulation between the studs, the house is wrapped with 1-inch-thick, foil-faced polyisocyanurate board to eliminate thermal breaks. A back-vented fiber-cement rainscreen cladding protects the house against moisture infiltration and acts as a built-in shading device by venting much of the heat accumulation, Saft says. A radiant barrier behind the rainscreen helps reflect any residual heat.
Topped with reflective metal roofing, the single-pitch roof accommodates a 3.24 kW thin-film photovoltaic system to help offset the cooling system's minimal energy demands—making the house active, as well as passive. While the Passive House approach avoids energy production as a method for reducing demands on the power grid, achieving net-zero energy performance—another of Saft's goals for the project—generally requires some renewable energy generation. "The beauty of Passive House is that you reduce energy consumption so much by conservation measures that you need only a small photovoltaic system," Klingenberg says.
Saft wanted to push the project's limits in an economical way to find out whether a Passive House project in the South could be financially sustainable, and all evidence suggests he's achieved just that.
"I wanted to find out whether these efforts are just for people who have lots of money, or if they can start to infiltrate the larger housing stock," Saft says. Judging by the results of Saft's project, it is possible. For less than $110 per square foot—financed through a conventional bank mortgage—and using only readily available construction materials, he built a three-bedroom, two-bathroom house providing a total 1,200 square feet of living space.
Three of Saft's architecture students currently rent the house, so the project pays for itself. They also help Saft track and monitor energy usage, temperature, humidity levels, quality of daylighting, and overall performance. The house was built by Jaron Young, a former student of Saft's, who formed his own company, HJ Design and Construction, after graduating.