This past weekend was a big milestone: we passed our initial blower door test, exceeding our airtightness target of 530 CFM @50Pa (a target based on Passive House standards as well as early energy analysis). Here’s what we learned about our air barrier.
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.)
We were pleased to host the Iowa chapter of the Building Enclosure Council (BEC) for a house tour and presentation, as well as a sustainable construction class from Hawkeye College. Many thanks to everyone who came out — including for the many excellent questions and kind words about the house.
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.
The house in coming together rapidly. With the exterior walls and roof complete, the interior is taking shape. It feels lovely: bright and open yet still intimate.
One of the goals for this house is durability: a lifespan of 200 years or more. Is concrete an appropriate material to achieve that aim?
First, some background: It’s not the concrete itself that’s problematic; it’s the rebar embedded in concrete. This rebar tends to corrode over time, and as it does, the rust increases the diameter of the rebar slightly, spalling the concrete, and eventually causing the concrete to fail. This is the main reason why Roman concrete (which had no rebar) has lasted for 1000s of years, whereas contemporary concrete’s lifespan is typically measured in decades.
Once we evaluated which passive design strategies were most important when it came to energy use and thermal comfort, we asked the question: which will give us the most bang for our buck? Rather than engage in a detailed (time-consuming) cost analysis at this early stage, we did a simple overlay on our existing sensitivity analysis — which provided some key insight for remarkably little effort.
Keep tabs on the construction with our live NestCam. You can view progress anytime at this link. The page refreshes automatically every two minutes: http://www.iowanest.com/nestcam/ If the image is black, it means it’s dark in Iowa, and the crew is probably sleeping.