Following Up on a Passive House in the Deep South
Completed in February, the 204House, in Louisiana, passes the big performance test
With Louisiana's summer weather starting to bear down on it, a 1,200-sq.-ft. house in the south-central part of the state designed to meet Passive HouseA residential building construction standard requiring very low levels of air leakage, very high levels of insulation, and windows with a very low U-factor. Developed in the early 1990s by Bo Adamson and Wolfgang Feist, the standard is now promoted by the Passivhaus Institut in Darmstadt, Germany. To meet the standard, a home must have an infiltration rate no greater than 0.60 AC/H @ 50 pascals, a maximum annual heating energy use of 15 kWh per square meter (4,755 Btu per square foot), a maximum annual cooling energy use of 15 kWh per square meter (1.39 kWh per square foot), and maximum source energy use for all purposes of 120 kWh per square meter (11.1 kWh per square foot). The standard recommends, but does not require, a maximum design heating load of 10 W per square meter and windows with a maximum U-factor of 0.14. The Passivhaus standard was developed for buildings in central and northern Europe; efforts are underway to clarify the best techniques to achieve the standard for buildings in hot climates. standards has so far been performing as designed.
GBAGreenBuildingAdvisor.com posted an item about the project back in February, as construction neared completion. The house has been variously dubbed “the 204House” or the “LeBois House.”
The project architect, Corey Saft, a professor of architecture at the University of Louisiana, provided us with energy efficiency details about the three-bedroom, two-bath house and said he was aiming for LEEDLeadership in Energy and Environmental Design. LEED for Homes is the residential green building program from the United States Green Building Council (USGBC). While this program is primarily designed for and applicable to new home projects, major gut rehabs can qualify. Platinum certification as well as certification by Passive House Institute US. Given Louisiana’s relatively long hot-and-humid summer season, achieving the latter goal seemed like an especially interesting challenge, as one observer, GBA Advisor Carl Seville, noted in the comments section of the post.
Taming the cost of dry comfort
But a recent story on the project posted by The Independent Weekly, which serves the Acadiana region of south Louisiana, explains that the house, while still awaiting word on LEED certification, was certified in June by Passive House Institute. Just as important, the house continues to provide a high level of interior comfort to its three occupants – students attending UL’s architecture school – and the home's utility bills hovered near zero in March and April (minus 62 cents, then $5). Over the course of a year, Saft estimates, utility costs likely will average less than $25 a month.
“There was a sense of relief, really,” Saft told the paper. “You don’t want to be too optimistic. I mean everything you read says one thing, but usually it never comes out that good. So I was definitely pretty surprised. It was hoped for, I wouldn’t say anticipated. It’s the first time this was done in a hot, humid climate where everything kind of worked out the way it was supposed to.”
Insulation, airtightness, and an ERV
The shell of the house features R-28 IcyneneOpen-cell, low-density spray foam insulation that can be used in wall, floor, and roof assemblies. It has an R-value of about 3.6 per inch and a vapor permeability of about 10 perms at 5 inches thick. LD-R-50 walls and an R-55 Icynene LD-R-50 roof, with 2x6 and 2x8 advanced framingHouse-framing techniques in which lumber use is optimized, saving material and improving the energy performance of the building envelope.. The exterior walls are wrapped in 1-inch polyisocyanurate, the roof in 2-inch polyiso. Siding is pre-painted fiber cement board and white standing-seam metal panels, with a 1-inch space between the siding and polyiso to help “shade” the walls and prevent heat and moisture buildup. R-21 extruded polystyrene (XPSExtruded polystyrene. Highly insulating, water-resistant rigid foam insulation that is widely used above and below grade, such as on exterior walls and underneath concrete floor slabs. In North America, XPS is made with ozone-depleting HCFC-142b. XPS has higher density and R-value and lower vapor permeability than EPS rigid insulation.) was used for the basement/crawlspace walls, and R-16.5 XPS under the slab. The house is fitted with SeriousWindows’ 501 series vinylCommon term for polyvinyl chloride (PVC). In chemistry, vinyl refers to a carbon-and-hydrogen group (H2C=CH–) that attaches to another functional group, such as chlorine (vinyl chloride) or acetate (vinyl acetate).-frame windows, with SeriousGlass 8 double-pane glass.
During full summer heat, the house will lean heavily on its energy recovery ventilator, an UltimateAir RecoupAerator, to reduce humidity and air temperature, but it also is equipped with a 1-ton ductless mini-splitA type of small-capacity heat pump (as little as a ton or even less) with a closely-associated outside compressor and inside evaporating coil (often through-the-wall in design). These heat pumps often come with variable-speed compressors and blowers,giving them excellent modulation for thermal comfort. These features also contribute to COPs of around 4 for ductless min-split heat pumps. They are also well-suited for ultra-high performance, small-volume homes. air conditioner with a single vent.
On pricing and appraisals
Saft said he aimed for affordability, and in fact construction and materials costs – including a 3.25 kW thin-film photovoltaic(PV) Generation of electricity directly from sunlight. A photovoltaic cell has no moving parts; electrons are energized by sunlight and result in current flow. system – came to a pretty reasonable $120 per square foot, although the architect emphasized in the Independent Weekly story that, as has been noted time and again by green builders, projects with high-performance features are still not abundant enough in most markets to appraise realistically.
“If you’re rich and you want to make a zero energy house, it’s not that hard. But the trick is to make it standard practice,” Saft told the paper. “For me, it’s making it cheap and staying inside the realm of standard practice, and that hopefully will inspire other people to do it. Hopefully, little by little, projects like this will help establish some precedents.”
- Corey Saft (image 1), Passive House Institute US (image 2)
Jul 10, 2010 6:45 AM ET
Jul 10, 2010 8:43 AM ET