A few weeks ago I attended a class called “The Zero Energy House.” Jon Passi taught the class for the Driftless Folk School, and is the owner and builder of the zero-energy home we learned about. The house is located a few miles outside of Viroqua, Wisconsin, and was built over the last five years or so.
Jon did a bunch of the work himself, including installing the photovoltaic and solar hot water systems. He said he spent about $180,000 and the house is off-grid, so there is a fair amount of hardware included in that price.
Here’s a view of Jon Passi’s zero energy home showing the front door, the sun room, and the solar thermal system to the left.
Jon built his home mostly conventionally, with poured basement walls, two inches of foam insulation below the slab, two inches of foam insulation on the exterior, and three inches of foam insulation on the interior. The solar hot water system feeds into a preheating tank, and then into a radiant heat system in the slab. There’s also a propane-fueled water heater, a small inline pump, and a backup boiler for baseboard radiators that Jon installed on the main floor and upper floor. The backup boiler system has never been used, but Jon said he installed it in case he wants to leave for an extended time during the winter sometime in the future. Jon reports that the radiant heat in the slab does an excellent job of controlling moisture in the basement, and I can attest that it was clean, dry, and warm on a rainy October day.
On top of this relatively standard basement, Jon built the framing with locally milled lumber. However, he said he would not do so again, as the lumber was not uniform in size, so he ended up milling every piece to size. You can imagine how time-consuming that was. The walls are insulated to about R-30 with open-cell spray foam, and the ceiling is insulated to R-50 with cellulose. Jon used Hardyplank siding and has been very happy with its durability and low maintenance requirements.
Heat comes from solar gain in the sunroom, and a woodstove on the main floor, in addition to the solar thermal heat in the basement slab. As for electricity, Jon installed a 3 kW photovoltaic system, with panels installed on the roof and on a ground mount. He said he really would need only about 1 kW for his needs.
Here’s a view of the ground-mount PV on the left, the solar thermal system farther on, and the recycled windmill in the distance.
Water comes from a well located 100 feet or so from the house, up a small hill. The windmill is an old model, perhaps 100 years old, and was refurbished and sold to Jon by an Amish man who specializes in old windmills. It feeds into a concrete cistern, which will be full in just six hours on a windy day. The cost for the windmill and cistern were around $8000, and Jon reports that they work well and he’s happy with them.
Two main ideas are sticking with me about Jon’s house: how normal it seems, and how feasible the whole project seems. I think most of us could pull this off.
Jon’s house looks utterly normal inside and out, with just a couple clues that it’s not. When you enter the main floor, you might notice the thick walls; the window sills seem to be about 12-15” deep. And as you walk around to the back of the house, you’ll see the photovoltaic panels and the solar hot water system. That’s about it.
Jon’s house, at about 2,500 square feet, seems oversized for one person. But it’s a more flexible size than a tiny home of 500 square feet, and is roomy enough to easily accommodate a family. And it seems that most families could handle this house just fine, as long as one person is willing to learn how to run the PV, solar thermal, and electrical systems. A smaller house would be cheaper to build and easier to heat, but this one may be easier to sell for use as a full-time home.
The main floor houses the woodstove, kitchen and dining area, and sunroom. The sunroom can be opened up and closed off with glass-paned French doors. I have had a similar space in one of my previous homes, and can attest that a properly designed sunroom can provide a great amount of free heat in cold, sunny weather. Without doors to completely close off the space, though, the sunroom will drain heat from the rest of the house after the sun sets.
The kitchen is the heart of the main floor.
The built-in dining table anchors the kitchen area; french doors to the sunroom are visible beyond.
The sunroom, with thermal-pane windows, warms up nicely on sunny winter days.
The second-floor has a bathroom and a couple large bedrooms, with a large open area that Jon uses like a living room.
The second floor houses two bedrooms, a bathroom, and this living area.
I like the solar thermal-radiant floor heat system, as the basement was quite comfortable. In warm weather you can simply shut it down and let the concrete mass cool. In cold weather the system can provide a substantial amount of heat, then automatically store it in the slab. I wonder about the cost, though, and its effectiveness in warming the second floor of the house. I also wonder if it would be cost-effective to install a loop for a wood boiler. It would be a redundant system, but would be functional when it’s cloudy. That’s a discussion for another day.
My main question in living with this house would be cooling. Sleeping in hot and especially humid weather is pretty sketchy for me. The bedrooms are upstairs, and I wonder if the windows can provide enough cross-ventilation. Fans can help a lot, but when it’s wicked hot out they’re just not enough. Maybe a mini-split system system would work to just cool the sleeping areas at bedtime. I’ve seen systems that draw only 900 watts or so in cooling mode, but more in heating mode. If that draws too much power from the PV system, I suppose I could sleep in the basement.
Diagram of a ductless mini-split heat pump system. Creative Commons photo courtesy of 3tonairconditioner.net.
The main ideas to remember with this house are these:
- A superinsulated and methodically air sealed house can look conventional yet work very well for creating a net-zero home.
- Superinsulating, air sealing, and passive solar design make heating the home much easier.
- The solar thermal and photovoltaic systems are more complex to manage than grid power, but it’s not that complex; just about anyone can learn how to run the systems in this house.
- Jon learned it all when he decided to build his own house! “I had no idea you could even run an entire house off solar ’til I did it, and the same with solar hot water. The alt-energy stuff still amazes me, because I used to think the kind of house I now live in was an impossibility, or that it only was for super-rich people.”
What would Jon do differently?
After living in a house, there are bound to be some features that could be tweaked. Jon said that he would make a few changes, as well, if he were to build again.
“I’d put a masonry stove in it to heat it, and I’d probably make it underground, or semi-underground, plus I’d put the well farther up the hill so I’d have better, free water pressure. I bought lots of lumber for the house from the Amish, because I wanted to use local wood, but I had to re-mill every bit of it, so I would probably not use local sawmill wood next time. I guess, other than that, I would probably do lots of things the same,” Jon said.
And now for another viewpoint
Jon’s house is efficient, comfortable, off-grid, self-built, peaceful, and livable. And since technology is changing year by year, and as more and more people are building zero-energy homes, I think it’s helpful to evaluate how the systems work. You’ll find different points of view, even amongst building science professionals, so many questions still don’t have definitive answers. But I’m going to include a couple of links that make me think about the options.
I still don’t know if the solar thermal/radiant heat idea is efficient or a good idea. The consensus online at Green Building Advisor is that a radiant slab is overkill in a superinsulated house; is that true with solar thermal heating it? What about the idea that circulating pumps are too inefficient so off-grid homes don’t use radiant heat?
What if Jon had built without the solar thermal and radiant heat, and instead had used a mini-split system with extra PV to power it? He would also have cooling with this system. His backup system is a boiler and radiators, fed by propane. Could he eliminate that, as well? What would heat the house if he were gone for two months in the winter, and it was cloudy for days at a time? I think one or two propane-fueled direct vent heaters would cost much less than the boiler setup, and would be fine as a backup.
Well, in Jon’s case, he’s already at the mercy of the sun god, as he needs the sun for power and for hot water. That’s why he has a wood stove for heat, as well.
Solar Thermal Is Dead
Heating A Tight, Well-insulated Home
Will One Radiant Floor Heat Two Stories?
My tentative conclusion after reading all these is that solar thermal and the radiant heating are not optimal. A better solution would be more PV and a mini-split system.
And finally, I’m waiting for interior photos and will post them when I get them.
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