Packaging Passive House

Passive House may not yet be a household name in the United States, but the European-born, ultra-energy efficient approach to building is making inroads here, and some of the credit must go to Adam Cohen. Founder of Roanoke, Va.–based Structures Design/Build and one of the country’s first Certified Passive House Consultants, the architect teaches the Passive House Institute US course for builders, the curriculum for which he co-wrote.

“We teach it six times a year around the country,” Cohen says. “A buddy of mine from Seattle and I spend four days, eight hours a day, teaching 30 people how to build a Passive House.” But Cohen’s goal is to do more than train 180 new Passive House builders a year. “It’s to change the world, it’s to change the way we build,” he explains. “And we won’t change the world at that rate.” To speed up the adoption process, Cohen has developed a modular design/build system aimed at making Passive House accessible to any builder—with no training required—and at a cost that’s competitive with conventional construction.

Modular details provide a flexible kit of parts.

Drawing on his experience in the studio and in the field, Cohen combined software-based architectural design with panelized construction to make “a very simple snap-together system.” An architect or designer creates a design using a set of modules: wall panels in 2-foot length increments and with two plate-height options; building corners; six windows that can be ganged in varied ways; and three door types.

Limiting the design palette greatly reduces cost, making it ideal for multifamily and production work, Cohen says. To make the process accessible to any designer, he used the popular 3D modeling program SketchUp. But he adds that the system offers designers a surprising degree of flexibility, which makes it fully applicable to custom building as well. “We have a $1.4 million house in design now, using all standard pieces except for five custom panels,” he says.

Prefabricated panels simplify construction.

Once a design is finalized, components are fabricated at the two factories with which Cohen has contracted. Wall panels consist of a 2x4 frame, insulated, sheathed, air-sealed, and covered with 6 inches of additional rigid insulation. To produce a building envelope that will meet the Passive House standard of 0.6 air changes per hour at 50 Pa of pressure, panels are joined on site with an expanding foam gasket (for vertical connections) and liquid-applied sealant (for horizontal joints).

Heavily insulated and air-sealed foundations are key to Passive House methods. Cohen has developed modular components—insulating forms for floating slabs and insulated concrete panels for basement foundation walls—that are cost competitive with conventional poured-in-place foundations. “We can set and pour a slab a lot cheaper now than we ever could with standard concrete forms,” Cohen says. “The system is so simple that if you can set a wall panel, we can show you how to set a panel in an airtight way. The only difference is you’re setting these gaskets in the joints.”

A smart system makes specialized training unnecessary.

“Builders will get a tractor trailer-load of panels delivered to the site, plus one of our staff to show them how to put it all together,” Cohen explains. The package, which has yet to gain an official brand name, includes super energy-efficient tilt-turn windows from Ireland—“It can be intimidating for builders to have to buy Passive House windows from Europe, so we’re importing them by the container load,” he says—but omits conventional materials, such as floor framing and roof trusses, that are easily sourced locally.

“All we do is the specialized Passive House stuff,” he adds. “Everything you can buy off the shelf, you buy off the shelf.” And if it’s desired, consultation on mechanicals is optional. When fully deployed, Cohen says, the system will allow any competent builder to produce houses that meet the country’s highest standards of energy efficiency and indoor air quality.

With his own construction crew, Cohen finished his first factory-fabricated project this past spring. Three more are scheduled for completion by early 2015, and Cohen plans to market his system to architects and builders later in the year.

“We needed to do it because people were afraid of [Passive House],” he says. “This takes away a lot of the uncertainty. It’s modular, repeatable, standardized, and simple. And there’s no special training required.”

- By Bruce D. Snider. This article was originally published in CUSTOM HOME November 2014.

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