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Best Green Houses:

The Windless City

Weiss Building & Development and Tom Bassett-Dilley
Chicago

Preempting air infiltration helped this home achieve Chicagolands first Passive House certification.

David Sokol
December 2013
Photo © Eric Hausman Photography

Brandon Weiss grew up on construction sites. Then he kept literally growing, reaching the lofty heights required of the basketball court. He played the game professionally in Germany and the Netherlands after college.

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Weiss’ athletic career first took him to Darmstadt, Germany, where the lifelong homebuilder in him was piqued. For instance, he wondered why his apartment building’s hall lighting remained on for only 45 seconds upon entry: If he couldn’t sprint to his fourth-floor flat in the allotted time, he would have to hit the reset button on a stairwell landing. A resident explained that, with common circulation occupied so rarely, it only made ecological sense to hook those spaces’ luminaires to timers.

This and similar revelations inspired Weiss to bring a more sustainable mindset back to the U.S. for a career after sports. He founded the spec- and custom-home company Weiss Building & Development in South Elgin, Illinois, in 2005 to pursue green building. Whereas the Darmstadt experience “opened my eyes to energy efficiency, in further research I also became passionate about aspects of environmental building science like indoor air quality, because athletes are always concerned about health.”

Chicagoland architects share that passion. One is Tom Basset-Dilley, an Oak Park, Illinois–based practitioner and president of Passive House Alliance Chicago. When Corinna and Rodrigo Lema from nearby River Forest requested a healthy new home fabricated in concrete from the architect and Passive House consultant, Basset-Dilley introduced the family to Weiss. The result of their work is a 3,600-square-foot home that is the first in the metropolitan region to earn Passive House certification.

Weiss and Basset-Dilley partnered at a very early design phase, so when they decided to aim for certification, they incorporated necessary tools from the start. “While Tom was designing he was also plugging everything into the Passive House Planning Package,” Weiss recalls. “With every move of a window, for example, we could find out how a change affected heat demand and solar thermal gain.”

Although there were more affordable stick-built solutions for energy efficiency, the client insisted on concrete construction. After determining that insulated concrete forms offered the most frugal green response for this project, Weiss says, “We really tried to tweak and bring the wall to Passive House levels.” To do so, the team, which also included Biltmore Insulated Concrete, relied on another high-tech platform: WUFI, or Wärme und Feuchte Instationär. German for Transient Heat and Moisture Transport, the software performs hydrothermal wall analysis using historical weather data.

“Achieving an airtight assembly means not allowing air leakage to be our source of drying. So we had to pay attention to water mitigation, flashing details, and making sure that materials can dry out if they do get wet,” Weiss says, explaining that even an impermeable building envelope can suffer from moisture problems, due to internal condensation via thermal bridging and other means. In addition to calculating insulation, then, “Knowing the drying potential is partially what the WUFI software is doing, too. It’s looking at assembly, even finishes, to make sure that the wall is diffusion open in both directions, which is important given the extreme summer and winter conditions in Chicago.”

From this modeling, a non-load-bearing 2-by-4 interior wall was mounted inside the insulated concrete forms and filled with 4 inches of dense-blown fiberglass insulation. The ICF structure itself comprises 2.75 inches of rigid expanded polystyrene (EPS) foam on each side of the 6-inch concrete core. It extends 5 feet below grade, to the house’s footings; that slab sits on 8 inches of EPS topped in a vapor barrier that was also taped to the ICF walls.

“You need a third of your R-value outside, without risk of condensation,” Weiss explains, and for that the concrete exterior was installed with 2 inches of Dow insulation that comprises 3-ply poly/aluminum foil facers laminated to a foam core. Argon-filled triple-pane windows included the same weather-resistant-coated product, and were sealed in tear-resistant flexible and straight flashing tape. Three-quarter-inch plywood furring strips were attached vertically every two feet between the exterior installation and engineered wood siding, to provide vented drainage for any moisture that might get beyond the visible cladding.

The wall assembly has an emotive quality, thanks to deeply inset windows that invite a lazy weekend read or, seen from outside, suggest warmth and coziness. Indeed, that suggestion is backed by reality, as the insulated walls perform—in tandem with a unique double ceiling that minimizes exterior penetrations—well enough to preclude $30,000 in mechanical systems. There is neither furnace nor air-conditioning. Instead, first- and second-floor ductless wall-mounted mini split heat pumps handily accommodate the 13,000 BTU maximum hourly heat load. Weiss says of the savings, “If your wall assembly employed WUFI correctly, you’re not going to have to maintain your insulation like you would with mechanicals. The one-time cost of the wall assembly becomes lower in light of the longer-term expenses you’re avoiding.”

There may be healthcare savings to consider, as well: Weiss included an energy recovery ventilator in the house to support the heat pumps, and he also points out that it twice-filters air, because “When you rely on cracks for fresh air, that’s not fresh air; it’s leaking through the darkest spots of your home.” In that same spirit, the house was continuously vacuumed out during construction, while subfloors and heat pumps were protected from sawdust and drywall dust until final-phase cleaning.

Weiss also made sure that interior finishes met the low- or no-VOC and formaldehyde-free requirements of the Underwriters Laboratories’ GreenGuard Gold program. The Lemas caught Weiss’ personal enthusiasm for indoor environmental quality, following his directions for sourcing healthy furnishings and products for their new home. And in something of a snowball effect, now the builder is aiming for his next project to be the first certified nontoxic Passive House in America. To accomplish it, “We are trying a couple different wall assemblies, learning the best way to air-seal certain penetrations with new weather-resistant barriers coming on the market from Europe.” The research requires another transatlantic journey, but this time the innovative thinking is being imported.

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