The term “passive house” seems somewhat redundant. Set on foundations, what could be more immovable, and therefore passive, than a human dwelling? Offering little resistance to heat, cold, wind, or moisture, it is passive by nature.
But to its advocates, the passive house signifies something specific, technical, visionary, and even … activist. To the architects, builders, remodelers, and planners who design and construct them, a “passive house” means a structure designed and built — or renovated — to use up to 90% less energy than the typical home. They’re hoping its time has come.
Passive-house construction sets out to achieve airtight construction with thicker walls and insulation thicknesses beyond code, as well as building components such as triple-pane glass windows and installation methods that guarantee a near-seamless building envelope. The net effect is to enhance thermal efficiency and minimize heat conduction.
Meanwhile, since a house normally “breathes” through its cracks, and in the case of the passive house there are none, a ventilation system — as key to the concept as airtight construction — keeps air within the structure fresh while using an energy recovery ventilator to capture and reuse whatever heat might ordinarily escape with air into the outside.
Use & Reuse Heat
So why passive? If built to the certification standards of the Passive House Institute, occupants can stay warm and comfortable in their built or renovated dwelling using and reusing the heat of its lights, appliances, and the sun that comes through windows. A passive house could conceivably do without a furnace or air-conditioning units, though that depends on where it’s located and is the exception, not the rule. For example, when completed at the end of this month, two mini split wall-mounted heat pumps will provide for the heating and cooling needs of the 3,598-square-foot house in River Forest, Ill., that is the first passive house in the Chicago area and the 28th certified by the Passive House Institute. “In this climate, there still needs to be a heat source,” says architect Tom Bassett Dilley, who designed the house. “But you don’t need to duct that heating around the house” since the ventilation system will distribute heat efficiently throughout the structure. (For periodic construction updates and details, see Bassett Dilley’s blog.)
Apart from reducing the owner’s energy bills, all this has a larger point that’s social, even planetary: to bring “a smarter way of building” into the mainstream of residential construction and, ultimately, to put a big dent into global warming, says Mark Miller, an architect and executive director of the Passive House Alliance, in Urbana, Ill., a sister organization to the Passive House Institute. While the Institute sets standards and evaluates for certification purposes the designer’s calculations based on its own energy modeling tool, the Alliance brings together building professionals who share their passive-house experience and technical knowledge. Close to 800 builders, architects, remodelers, and engineers belong to the Alliance.
Cost-Effective Building Standard
The passive-house movement may be generating curiosity and interest, but it’s not new. The concept actually originated in the U.S. in the 1970s and soon gathered a lot more attention and support in Europe, especially Germany and Sweden. In the early ’90s, computer modeling — which takes into account variables such as site orientation, openings, and R-value of wall assemblies — made the idea fully functional. Bassett Dilley says that when he found out in 2009 that there was a software package that allows you to monitor the energy impact of your design, he thought: “You mean I don’t have to wait for an engineer?” His next passive house project is a whole-house remodel in rural Wisconsin.
Miller says that the passive house movement would be far more widespread except for recession and the drastic slow-down of the housing market. Now, with recession waning and the effects of climate change becoming increasingly real — the Environmental Protection Agency says that greenhouse gas emissions in the U.S. rose by 10.5% between 1990 and 2010 — passive house advocates feel their time has come. Miller notes that residential energy consumption — half from heating, ventilation, and air conditioning, the rest from the energy that appliances consume — accounts for a significant portion of greenhouse gases. According to the Center for Climate and Energy Solutions, residential buildings account for 17% of U.S. greenhouse gas emissions.
“The mission of passive house is about stopping climate change,” Miller says. “We want to wean residential construction off of fossil fuels by making the house more eco-friendly.”
Some components for the River Forest project, such as its triple-pane windows, were sourced from abroad. The mini heat pumps are manufactured by Mitsubishi, and the heat recovery ventilation system made by the Swiss company Zehnder. But “North American manufacturers can get pretty close to this performance level,” Bassett Dilley says, specifically about the windows, and most of what builders and remodelers would need to make a house “passive” is made in the U.S. and is readily available, as for instance the several inches of Dow insulation applied to the exterior. “People are starting to hear about it,” he says. “It will spread more and more when they realize it’s a cost-effective building standard.”