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.
Continue reading Is Concrete Durable?
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.
Continue reading Is Net Zero Energy Achievable? A Pre-Design Investigation
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.
Continue reading Sensitivity Analysis: A Step-by-Step Guide
I’ve had several requests to post additional images of the house design — so here are the floor plans and exterior elevations. Enjoy!
Continue reading Plans & Elevations
Before I ever put pen to paper for this project, I wanted to answer a deceptively simple question: What passive design measures are most important? What basic strategies did the design need to employ to be successful? —to maintain human comfort with a minimum of added energy?
It’s important to answer this question before design begins in earnest for two reasons:
- With a limited budget, it’s important that we invest in the right things; and
- If we know the most important strategies before we start designing, we can incorporate them into the DNA of the design—often more effectively and at lower cost than if they were afterthoughts. For instance, if thermal mass or natural ventilation is important, these things will begin to dictate the construction or interior layout in ways that are difficult to “add on” later.
Continue reading What Passive Strategies are Most Important? Using Simple Box Modeling to Inform Design
This webinar from December 2015 provides an overview of the design processes and analyses that were used to set the project on track toward Net Zero Energy during Conceptual and Schematic Design. The studies include “simple box” energy modeling to determine the best passive design measures, comparison of design options, analysis of shading strategies, and optimization of envelope parameters like R-values and glazing. I used a variety of tools including Climate Consultant and the CBE Thermal Comfort Tool — but mostly I used Sefaira Architecture. (Full disclosure: I worked for Sefaira for nearly five years; that’s where this webinar comes from originally.)
I’ll be going into more depth on these studies in future posts, but this webinar is a great overview.
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.
Warning: this link can be surprisingly addictive. This tab stays open on my computer at all times.
Continue reading NestCam Live Construction Camera
The Iowa Nest is a Net Zero Energy-targeted residence in rural Iowa. It is designed to supply 100% of its energy needs; to be comfortable without conventional air conditioning; to fit into the landscape; to last for hundreds of years; and to do all of this on a conventional construction budget.
This blog will be run jointly by me (Carl), the primary designer, and by the owners, Peter and Jen. Our hope is to share our experiences designing and building this house so others can learn from our mistakes and re-create our successes. Our experience has shown us that it is possible to achieve remarkable performance (and great design) with a reasonable budget — and we hope to show others how they can do this, too.
You can subscribe to our mailing list to get regular updates: just send an email to email@example.com.
Let’s start by taking a closer look at the project’s design goals.
Continue reading Iowa Nest Residence: Net Zero Energy at Conventional Cost