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Seven Strategies for Net Zero Energy at Net Zero Cost

We set out to design a Net Zero Energy house at conventional per-square-foot costs. We got pretty darn close. Sans solar panels (which will be installed after two years of operation), the house came in at 8% less than a conventional new home. With solar panels, the house is still 2% less than conventional.

Here’s a full cost breakdown, and the seven strategies we used to get there.

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A Wood Stove in a Passive House

How should you design and detail a wood stove in an airtight Passive House? Here are some of the considerations, and the approach we used on this project.

First off: should you even have a wood stove in a Passive House? This is rightly a matter of some debate. It’s certainly not necessary, as our temperature data have shown: this particular house has proven it can stay habitable even through the coldest of cold snaps—maintaining ~55 degF even in -20 degF outdoor temperatures without mechanical heating.

And, a wood stove in a Passive House comes with downsides and risks:

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Slideshow: Achieving Net Zero Energy at Conventional Cost

Below is the slideshow I presented on April 20, 2017 to the Iowa Building Enclosure Council, and to a sustainable construction class from Hawkeye Community College.

The version below is slightly edited to make it easier to follow online. (I tend to avoid text in my presentations, which can make them difficult to follow without accompaniment.)

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A House That Maintains Its Own Temperature

We’ve added temperature and humidity sensors to the house in three locations, so we can start to track the home’s actual measured performance. While these sensors will be most useful once the house is complete, the data that’s coming back now is already interesting, and is already showing the effectiveness of the passive design measures.

For those interested, you can track the live data here: http://www.iowanest.com/monitor/

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Installing Zola Windows

I was on-site last week (Jan. 9-10) for the installation of Zola windows. This was both exciting and nerve-wracking for a few reasons:

  • Installing the windows correctly is critical to both the water management strategy and air tightness of the house. I wanted to make sure the details I had drawn actually worked out in practice.
  • The windows are massive. Each panel of the large lift-slide doors weighed 1000 lbs., and the second floor study window was 800 lbs.
  • The windows are one of the most expensive line items for the entire house. The possibility of damaging them was a bit scary.

Further complicating the process were extremely cold temperatures, and one day of rain (just enough to cover everything with mud).

In charge of the installation was Harry Schilling of Schilling Construction. I was incredibly pleased with Harry’s work and would highly recommend him for other projects. He and his team were fast and efficient while also paying close attention to detail. Harry also taught the owner and his assistant how to perform the installation, so they could help out with many of the steps, thereby reducing the labor costs.

Here’s how the windows were installed — both in theory and in practice.

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