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.
It’s now been a little over a month since we’ve been gathering temperature and humidity data from the still-not-complete and still-unconditioned house. I previously wrote that the early data seemed to show more stable, and generally warmer, indoor temperatures. That story is now even clearer.
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/
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.
I incorporated energy and daylight analysis as part of the conceptual design for the Iowa Nest Residence. This meant that early design discussions encompassed both traditional topics like floor plan layout, siting, and aesthetics, as well as performance criteria. The addition of analysis added a trivial amount of time, but proved incredibly valuable. Here’s how I did it — and what I will do differently next time.
Iowa, like much of the American Midwest, has a treacherous combination of deep, cold winters and hot, humid summers. Could we overcome this with good passive design? Could shading, natural ventilation, earth berming, and the like obviate the need for air conditioning?
Here’s how I went about answering this question. This analysis was done in early design so that the answer could inform basic design moves.
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.
We knew we wanted a Net Zero Energy house — but was this a feasible goal? What would it take to deliver? Here’s how I investigated this question before we even had a design in hand.
In my post on passive strategies and simple box modeling, I showed how sensitivity analysis can be used to identify the most important passive strategies while still in the pre-design phase. In this post, I’ll show in depth how I did that analysis.
For reference, here is the end product: graphs showing the potential impact of a number of individual strategies.