Acorn Glade: Chicago Area’s Third Passive House

After working with architect Tom Bassett-Dilley on several renovations, Jennifer Talarico and Tom Smith were about to embark on their home's final and most expensive overhaul. The couple has always been sensitive to environmental concerns and their impact. "Jen was in an environmental club in college," says Smith, "and I grew up during the oil embargo in the 1970s, so conserving energy is in my DNA."

Then, the couple discovered Passive House design. Passive House building, Smith says, "is about using conventional construction more effectively. That's very appealing. Certainly, the energy efficiency is the cornerstone of process, and ultimately your energy costs are low."

So, the couple asked Bassett-Dilley, principal of Tom Bassett-Dilley Architects in Oak Park, IL, about Passive House design. "Tom got super excited," Talarico recalls. "Knowing what we'd put into the house and what we'd still needed to do, we wondered if Tom could design a new Passive House for us. It quickly became clear that we'd be spending the same amount of money, whether we renovated our old house or built a new home. With new, we'd have a house designed just for us with cutting-edge environmental sensitivity and energy efficiency."

By Camille LeFevre, Rise Writer

7 min read

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Acorn Glade Exterior. Photo Credit: Eric Hausman Photography

What Is The Acorn Glade Passive House?

The Acorn Glade Passive House is a new, modern 1,800-square-foot home, located in Downers Grove, IL. It was completed in 2017. You can read about the homeowner's process on their blog. The house has received PHIUS and PHIUS+ Source Zero certifications.

Homeowners earn Source Zero after achieving PHIUS+ targets by integrating additional air-tightness, space-conditioning, and source-energy-limit building-science principles. Reaching PHIUS+ Source Zero, according to the PHIUS website, is "a holistic view" that "pursues both radical load reduction and clean energy production, allowing faster convergence toward the goal of eliminating carbon emissions from building energy."

Bassett-Dilley founded his firm in 2006 to meld sustainability with contemporary design, grounding his work in region, climate, and context. The firm designed the first certified Passive House project in the Chicago region. Talarico and Smith's home is the third Passive House in the area. The team designed the house, called Acorn Glade, "using the metaphor of the acorn," explains Bassett-Dilley, "so it harmonizes with its site, which includes views to mature oak trees, via a two-level structure that peels back."

What Technologies Were Incorporated Into The Acorn Glade Passive House?

Evolutionary Home Builders constructed Acorn Glade's walls with mineral wool batts, an air-tight layer of plywood with a fluid-applied air barrier, 6 inches of EPS cladding, and a vented rain screen with fiberboard cladding, prefinished wood siding by LP SmartSide, and corrugated metal siding, achieving R-45. The floors, which are R-21, include:

5-inches of EPS below the 4-inch slab.
An air-tight layer of 15 mil poly above EPS vapor control.
15 mil poly above the EPS.

The roof includes trusses with loose-fill cellulose insulation and interior taped plywood to reach R-87.

Zola windows and doors add to the home's air-tightness. A CERV smart ventilation system ensures healthy indoor air quality. Two ductless Mitsubishi mini-splits (one upstairs and one downstairs) provide additional heating or cooling.

Lessons Learned

Initially, the house only had one mini-split, which wasn't sufficient. "We calculated what the thermal bridging would be, so it wasn't unexpected or significant," explains Bassett-Dilley, but "the comfort issues on the lower level were essentially from cold air spillage from the indoor heat pump water heater and lack of a mini-split downstairs." Bassett-Dilley studied the issue, consulted with engineers and manufacturers, then summarized the issue and his proposed solution during his talk at the National Passive House Conference in 2019.

Instead of a single mini-split, which was unducted and not distributing the warm air sufficiently, Bassett-Dilley had a single mini-split installed on the second floor. "We learned, for future Passive House projects," he says, "that we need to add additional mini-splits, or we need to duct one or two."

Healthy Home Initiative

The CERV maximizes indoor air quality with air exchanges three times an hour. The homeowners also chose furnishings and finishes that meet the standards of the CDC's Healthy Homes Initiative.

"We have a little boy whose health is of paramount importance to us, and we want to remain healthy ourselves," says Talarico.

Acorn Glade Lower Level. Photo Credit: Eric Hausman Photography

Bassett-Dilley organized the home's interior to the south, which opens to a courtyard-like patio. A backdrop to this opening, which lets plentiful light into the house, is a wall of walnut harvested from trees on site. Walnut from the property was also used in the stairwell. Salvaged wood and concrete floors and stone countertops; no-added-formaldehyde panel materials; no-VOC and non-toxic paints; and GREENGUARD certified sealants, caulks, and adhesives add to the home's superior indoor air quality.

Adding Solar

Initially, says Smith, "solar wasn't part of the equation. It's not required to meet Passive House certification." Having an all-electric house, however, is required. "So, solar was a dream of mine because we also wanted to achieve net-zero."

The home's 36 roof panels produce approximately 1,300 kWh per year and power the house and the family's Tesla. The home has a grid-tied array "because Illinois doesn't allow you to be off-grid," Smith explains. "We do feed energy back into the grid, which is required. I'd like to get battery storage at some point, to keep more of what we generate."

As a PHIUS Source Zero house, monitored results show Acorn Glade uses 86 percent less energy overall, including all household energy use and electric car charging.

Costs and Returns

Talarico is pleased with her "right-size home. There's very little I would have done differently." Her husband, however, isn't happy about the internal heat pump hot-water heater, as it makes a noise that filters into the family's tv and music room. "I would rather have had an external compressor," Smith says.

He also wishes they would have included solar from the start, "as we would have shifted the exterior and the shed roof to accommodate the solar panels better."

Still, the family is happy with their choice to build a Passive House with solar providing all the energy they need for their electric home. "The cost was about 10 percent more than traditional construction," Smith says, "but part of the idea of Passive House is you're investing in the environment upfront, so you're not paying much in energy costs down the line."

There's isn't any good reason not to do it.

Costs and Returns

He also wishes they would have included solar from the start, "as we would have shifted the exterior and the shed roof to accommodate the solar panels better."