This Minneapolis Passivhaus Deals With Temperature Extremes

One often hears the original Passivhaus concept was designed for a temperate middle European climate where it's never too hot or too cold. That's why Tim Eian's Good Energy Haus in Minneapolis, Minnesota is so interesting: The Twin Cities have the coldest average temperature of any major city in the continental U.S. It's also hot and humid in the summer. Eian's house has bigger windows than I would have thought possible in such an extreme climate.

Eian presented his house at the recent North American Passive House Network (NAHPN) conference, where certificates like these are holy writ, demonstrating that the building has hit Passivhaus targets of energy consumption per square meter per year. Many early designs had lots of south-facing glass to maximize solar gain to reduce the amount of energy required. But this is harder than it seems. In early Passivhaus designs, the windows would often lose more heat at night than they gained in the daytime, and they would overheat terribly in summer.

Windows are also an aesthetic problem for architects; they are often sized according to how they should look on the street rather than how they perform. Designers generally want them bigger than the Passivhaus spreadsheet wants them to be.

The consensus these days seems to be that windows should be designed around the view—make them as big as you need them to be to be visually connected and comfortable inside.

And then we have the Good Energy Haus from TE Studio; the windows dominate the interior space, wrapping right around the corner of the living and dining area and running up the lightwell to the second floor. They are huge. How is this comfortable in a Minnesota winter? How is this possible in Passivhaus?

According to Eian, it is very comfortable indeed. Not just thermally, but emotionally. Between the heat, the cold, and the mosquitoes, Minneapolis can be uncomfortable outdoors for six months of the year; the living and dining area feels more like an enclosed porch than a living room.

The imported German windows are also extremely high quality, triple glazed, argon filled, with reflective coatings that keep the heat inside; the interior temperature of the glass never gets below 60 degrees. The coatings reflect radiant heat back into the living space so it never feels cold sitting next to them.

Not only that, they are so efficient that the south-facing windows retain about twice as much heat as they lose; the east and the west windows are a wash. On the north side, there are only small, fixed windows, which are more efficient than opening windows.

To prevent overheating in summer, there are motorized insulated shades that can be adjusted to maximize light while cutting direct sun. They can be operated manually or programmed.

So if you are willing to pay for the very best windows, you don't have to consider window size a limitation, even in Minneapolis.

In the ground floor plan, you can see some of the other features of the house. There is a bedroom/ home office and a full bathroom, good planning for aging in place; an oversized garage that is insulated and tempered so that electric cars never have to freeze; and a big utility room since there is no basement, which is framed with extra material and care so that it can work as an emergency shelter in storms.

When asked about the lack of a basement, Eian noted their last house had a basement and there was nothing in it but the furnace, and most people just use them for storage. He's got the utility room and the big garage so there was no need to build and maintain the extra space.

Architect Bronwyn Barry has a Twitter tag that describes the look of the Good Energy Haus: #BBB or Boxy But Beautiful. It is simple as it could be, a box with punched windows, set off by the covered entry and carport. In Passivhaus design, every jog and bump can be a thermal bridge and air leak and adds complexity to the analysis and the construction. It's clad in the simplest of materials: commercial corrugated metal and a bit of wood.

It is a simple section too, with 18 inches of I-joists used as studs and filled with dense-pack cellulose in a double-wall system that is probably becoming a North American standard for cost-effective Passivhaus construction; the outer wall is continuous and is doing nothing but holding up the insulation and the exterior siding. Above grade, it is all just engineered wood and cellulose. It is a complete wrap of insulation; even the footings are wrapped in foam and are warm and toasty.

I was surprised to see a dehumidifier on the wall of the mechanical room; the house has a heat pump, which is essentially an air conditioner that runs backward for heating, and AC units dehumidify as well as cool. Eian explains that "it's simply from the fact that the more efficient the house is, the lower the cooling requirement and the run time was too small to do dehumidification efficiently." So below 75 degrees and 58% humidity, the dedicated dehumidifier does a better job.

There is a lot to admire in this house. It's not too big. It's #BBB. It looks warm and comfortable, at least when I look away from all those windows. It is a great demonstration of how to build an efficient and attractive house to the highest standard in the coldest climates. I often wonder why everyone doesn't do this.

Enjoy a video tour done for a 2020 Passivhaus conference and see more at TE Studios. Besides being Eian's home, the house is also a demonstration project, being "the first urban infill, climate-neutral, certified Passive House Plus in Minneapolis." So it is good exposure for a team of contractors, suppliers, and manufacturers.