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Net Positive Home in Saint Paul, Minnesota
When Muffi and Tim Abrahamson moved to Saint Paul in 1989, they bought a large home on a double lot. They had always planned on building their own home on that lot, but Tim's busy remodeling business and Muffi's homeschooling of the couple's two children nixed that plan. Besides, the kids loved playing on the lot with its tree fort and sandbox. It was a popular gathering place for youngsters in the neighborhood.
When the kids grew up and moved out, the Abrahamson's revisited their dream of building a sustainable home. In 2016, they finished their new, low-impact, net-zero home on the adjacent lot and sold their former home.
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"It was good we waited," Muffi says. "Tim always wanted to build an energy-efficient home, and now the technology is available to reach net-zero." Moreover, Tim adds, "We realized if we sold the house and lot and moved elsewhere, someone would eventually build here and probably wouldn't construct an energy-efficient house. We also wanted the house to fit into the neighborhood, which we love and didn't want to leave."
During construction, Tim served as the general contractor. Both Abrahamson's designed the interior space and the home's exterior appearance. Their friend, architect Lucas Alm of ALM Design Studio in Saint Paul, designed the home's thermal envelope.
"Lucas and his team provided the energy modeling and the structural and thermal design," Tim says. "He also consulted with us on our design work and kept us from making mistakes. Combining solar panels, super-thick insulation, and good design, the 2,079-square-foot house is a good neighbor that inspires others to think about sustainability.
Passive and Active Solar Design
The home's design includes a simple rectangular form clad in cedar, with a metal gable roof and welcoming front porch, to blend into the neighborhood of traditional homes. While the City of Saint Paul requires 15 percent of glazing on the front of a new house, the Abrahamson's home faces north, and north-facing windows are usually minimized in passive houses, as they're net energy losers (in the northern hemisphere). The couple was able to acquire a variance. "We have 10 percent glazing, and the porch helped the front elevation feel welcoming to the street," Muffi says.
Most windows are at the back of the house, facing south, where a façade of nearly floor-to-ceiling windows captures passive solar heat gains. The windows look out onto two mature oak trees, which provide summer shade. “We sited and designed the house to draw in light in the winter,” Muffi says, “and when the sun is higher in summer, the oak trees keep the sun from overheating the house.”
A 7.57 kilowatt (kW) solar panel array on the garage roof is tied to the grid. The solar array acts as a mini power plant: In the spring, summer, and fall, it produces more energy than the house consumes; in the winter, the home consumes more energy than the array produces. Over a year, the house produces more energy than it consumes, making it net positive.
Camille LeFevre
Camille LeFevre is an architecture and design writer based in the Twin Cities.
