High-Performance Homes
Passive House Raises the Bar
LEED used to be the buzzword for energy-efficient homes in the United States, but a new standard in town could be a game-changer: Passive House. This construction standard is the toughest one yet, requiring very low levels of air leakage, very high levels of insulation, and windows with a very low U-factor.
Passive House has its roots in North America, but it blossomed in Europe (see timeline), where it has been an accepted standard for the last 18 years.
“Passive House has certainly taken a big foothold in Germany and Austria and other [European countries],” says Mike Duclos, a Certified Passive House Consultant (CPHC) and principal of DEAP Energy Group in Stow, Mass. Europeans tend to view their homes as long-term investments of 50 years or more, rather than possessions they’ll outgrow in three-to-five years. “That’s why, in the U.S., Passive House is a slowly growing, organic movement,” Duclos says wryly.
Are You Ready for Passive House?
If you’re getting involved in a Passive House project for the first time, here are a few things to consider:• Become a Passive House consultant. PHIUS offers both virtual and in-class training tailored to North American climate variations, market conditions, and building components.
• Invest in the software. The Passive House Planning Package (PHPP) is available for $225 from either PHIUS or the U.S. Department of Energy. The PHPP calculates energy demand for high-performance buildings. Among other things, the spreadsheet-based software provides data needed to determine a home’s heating and cooling loads and properly size its heating and domestic hot-water systems.
• Precertification is required while the home is still in the design phase. After construction is completed, a field test will be performed to ensure the home meets all parameters.
• Get ready for a learning experience, says CPHC Mike Duclos. “Think things through in the beginning, and have a good plan. If you can pull somebody into the team who has done one of these before, that’s a plus.”
The base theory of Passive House design and construction can be summed up as follows: maximize gains and minimize losses.
“You maximize gains via passive solar heat gains and internal heat gains from mechanical systems and occupants, and minimize losses via a thick insulated building shell and a great airtight layer achieved through air sealing,” says Eric Barton of Biltmore Insulated Concrete, Highland Park, Ill., a CPHC and Passive House Institute US (PHIUS) Certified Builder who constructs super energy-efficient building shells. “This keeps the internal heat gains within the building envelope and living areas.”
Barton points out that because the specific space heat demand and specific primary energy demand requirements are the same for all climate zones, it’s easier to achieve Passive House standards in a mild climate, such as San Diego, than in a very cold climate such as Duluth, Minn.
Most builders say achieving the standard requires an additional upfront investment of 5-to-10 percent. But Falmouth, Mass., builder Christian Valle says, “The overall incremental costs are not as significant as one might think. The tradeoffs of building a tighter ‘mousetrap’ result in smaller HVAC systems, among other things, which help offset other costs.”
While Passive Houses are more challenging to build than standard homes, Valle believes that as more builders get on board, the learning curve will shorten. “The building industry has trended toward energy-efficient construction, driven by clients and more rigid energy codes,” he says. “Builders are paying attention to air-sealing and insulation details. That’s what Passive House is really about, in a nutshell.”
As the movement gains momentum, though, American window makers are going to have to up their game.
“We don’t make great windows in this country, but that’s starting to change,” Barton says. “Some manufacturers are stepping up to the plate.”
Reading, Mass., architect Steven Baczek collaborated with Duclos on the Massachusetts home featured here. Baczek laments that “nobody [in the U.S.] makes a cheap, triple-glazed, Passive House-certified window. Your window package is going to go from $20,000 to $45,000. On the other hand, $300 a year to heat, cool, and supply hot water for a 2,000-square-foot house is pretty amazing.”
Extreme Energy Savings
Valle Group’s first Passive House was built for a client who was firmly committed to a rigorous standard of energy efficiency. The home sits on six acres of wooded land in East Falmouth, Mass., and includes a large organic garden.
Photos: John L. Moore
The 2,000-square-foot home has 17-inch-thick exterior walls. The R-values surpass those of a conventionally built home: R-105 in the ceiling, R-72 in the walls, and R-77 in the floor. The custom-built, triple-pane windows, which were made in Canada and shipped to the site, feature different glazing techniques depending on their location in the house. They allow for maximum solar gain on the south elevations and minimum heat loss on the north elevations. As a result, says Baczek, 57 percent of the home’s heat energy is generated by the windows.
“The biggest challenges of building this home were the tolerances we had to meet for air leakage, mechanical system design, and insulation values, and the unbelievable attention to detail required during all phases of construction,” says Christian Valle.
The 2,000-square-foot home has 17-inch-thick exterior walls. The R-values surpass those of a conventionally built home: R-105 in the ceiling, R-72 in the walls, and R-77 in the floor. The custom-built, triple-pane windows, which were made in Canada and shipped to the site, feature different glazing techniques depending on their location in the house. They allow for maximum solar gain on the south elevations and minimum heat loss on the north elevations. As a result, says Baczek, 57 percent of the home’s heat energy is generated by the windows.
Valle Group used a combination of insulation types including blown-in cellulose, blown-in fiberglass, and rigid insulation. The virtually airtight home was subjected to several blower-door tests during construction to detect and eliminate any leaks. The cumulative leakage of the entire home was the size of a playing card, versus a sheet of plywood for a comparably sized, conventionally-built home.
A heat-recovery ventilator captures heat from stale exhaust air and introduces it back into the house through incoming fresh air. The home’s heating load is minimal, allowing a high-efficiency, electric air-source heat pump to be used in lieu of a boiler or furnace. The actual heating load of 8.6 million BTUs per year is at least 50-percent lower than the annual heating and cooling energy consumption of a similar home in the same climate zone, Valle says.
At press time, Valle Group was in the design and precertification process for two more Passive Houses. Construction is expected to begin in the next few months.
First in Chicago
As a college student, Brandon Weiss played professional basketball in Europe. One of the towns he played in was Darmstadt, Germany, home of the Passivhaus Institut. “That really opened my eyes to a better, more efficient, and more durable way of building homes,” Weiss says.
Photos: Tom Bassett-Dilley
The clients wanted a concrete home, which is not a requirement for Passive House certification but does add significantly to its durability. Insulated concrete forms (ICFs) run from the footings to the roof. “Part of the [reason] we did so well on airtightness is the ICFs,” says ICF contractor Eric Barton. “When you pour the concrete into the ICF blocks, it naturally fills the void, creating an airtight exterior building shell. In a wood-frame house, we would have had to tape all the seams and plywood butt joints. Here, all we had to worry about was taping around the windows for the air sealing.”
Today he runs Weiss Building & Development in South Elgin, Ill., and has a long list of certifications including Graduate Master Builder and LEED AP. Weiss recently built Chicago’s first certified Passive House—a 3,598-square-foot, three-story home in suburban River Forest.
A Brief History of Passive House
1970sThe phrase “passive solar house” is coined to describe houses with extra thermal mass and extensive south-facing windows; demonstration houses are built in the U.S. and Canada.1988A conversation between Swedish professor Bo Adamson and German physicist Dr. Wolfgang Feist leads to development of Passivhaus standard.1991Feist builds first Passivhaus prototype in Darmstadt, Germany.1996Feist founds Passivhaus Institut and obtains funding for major research project involving hundreds of houses all over Europe.2003German architect Katrin Klingenberg builds home to Passivhaus standard in Urbana, Ill., and goes on to found Passive House Institute US.2006America’s first certified Passive House is built in Minnesota.
The clients wanted a concrete home, which is not a requirement for Passive House certification but does add significantly to its durability. Insulated concrete forms (ICFs) run from the footings to the roof. “Part of the [reason] we did so well on airtightness is the ICFs,” says ICF contractor Eric Barton. “When you pour the concrete into the ICF blocks, it naturally fills the void, creating an airtight exterior building shell. In a wood-frame house, we would have had to tape all the seams and plywood butt joints. Here, all we had to worry about was taping around the windows for the air sealing.”
Normally a builder would drywall the undersides of the plywood roof trusses, but in a Passive House the trusses are laminated with ½-inch plywood or OSB, and all the seams are taped. “That helps create an airtight layer on all six sides, which is one of the key details and differences between Passive House construction and conventional construction,” Barton says.
Determining the correct shape and orientation of the windows and the amount of shading required was critical, says Oak Park, Ill., architect Tom Bassett-Dilley, CPHC. His efforts were aided by a solar pathfinder—an engineered glass dome with a grid superimposed underneath it. “We took photos at the center point of each façade at the second-floor level,” he says. “It’s not just the south side that matters; all four sides matter in terms of radiation, both direct and indirect.”
In a blower-door test, the home achieved 0.39 ACH (air changes per hour) at a pressure of 50 Pascals, well within the minimum Passive House criteria of 0.60 ACH. Bassett-Dilley says there are no cold spots: “No part of the house gets below 62 degrees, even when it’s zero degrees outside. One pellet stove can heat the entire house.” There’s no need for a furnace or air-conditioning units; instead, two small ductless, wall-mounted, mini-split heat pumps satisfy the minimal heating and cooling needs.
Weiss focused on indoor air quality as well as energy efficiency. He used drywall that absorbs VOCs in the air and no-VOC sealants, caulks, and adhesives. “We gave [the house] a two-week flush-out period after construction was finished,” he says, to ensure there were no chemical fumes or particles left in the air.
The energy-recovery ventilator provides a continuous stream of fresh air to all of the living areas. “Stale or humid air is always being exhausted from the bathrooms and kitchen,” Weiss says. “The air quality in Passive Houses has been shown to be superior [to code-built homes].”
Urban Renewal
Tim McDonald believes Passive House is best suited for large-scale multifamily, urban buildings, and needs to be promoted as such. Long a proponent of sustainability, McDonald’s company, Onion Flats, was one of the first to design and build to LEED Platinum standards in Philadelphia.
“Passive House is just a natural extension,” says McDonald, a registered architect and CPHC. His group has built three certified Passive House projects to date and has three more in the pipeline. “LEED is a great holistic program to deal with sustainability, but [Passive House is a better tool for] getting down and dirty about how you actually reach net zero.”
The company’s projects include Belfield, a trio of HUD-funded rowhouses for low-income buyers; and The Stables, a 27-unit, market-rate townhome project. The 1,920-square-foot, three-story Belfield homes are 100-percent occupied. To date, two homes at The Stables are sold and two more sales are pending. Prices start in the mid-$700,000s for the four-story townhomes, which are approximately 2,500 square feet and include optional finished basements.
“We designed [both projects] to be built in a modular factory with conventional framing techniques, and we specifically designed this building system so that it could be built with no cost premium,” McDonald says.
The Stables was developed by Onion Flats as a joint venture with Domani Developers. The building generates its own power from a 4.23 kilowatt solar PV array, and the site is 95-percent permeable with green roofs and porous paving for stormwater management.
Finding materials has been a bit of a challenge, McDonald admits: “We couldn’t find [the windows we needed] in the United States. And we had to invent our own mechanical systems with off-the-shelf components.”
