The MCNZH foundation. The rectangle that's jutting out is the cold room, located under the front steps/landing.
A frequently asked question regarding the Mill Creek NetZero Home (MCNZH) is: "Why didn't you use Insulated Concrete Forms (ICFs) for the foundation walls?". The short answer is: "using traditional concrete forms and innovative insulating techniques, we can achieve a much higher R-value for less money".
ICFs are concrete forms made of styrofoam that you set up, pour concrete into, and leave in place to act as insulation. Here's a picture of someone setting them up:
The advantages of ICFs include decent insulation value, ease of learning for the do-it-yourselfer, and ease of setup (foam is a lot lighter than plywood).
There is a myth that ICFs provide walls with an "equivalent energy loss performance" to an R 50 wall. The argument goes that the mass inside of the concrete walls acts as heat storage, thereby buffering heat as it goes in and out of the building. The counter-argument is quite complex, but suffice to say that I've heard very knowledgeable people say that ICFs performing like an R 50 wall is complete bunk. The argument makes sense, too. When it's minus 20 outside, the relatively small amount of thermal energy stored in a concrete wall will have little effect. R value is R value. ICFs provide about an R 22 wall, with no thermal bridging. That's pretty decent, but it's not R50.
The foundation walls for the MCNZH will be insulated to about R 49 - actually R 49, no caveats or stars beside that term. We had the walls poured conventionally - with plywood forms - in August (see picture at the top), and before we poured the basement slab Peter Amerongen's crew glued 5 inches of ozone-friendly foam against the inside of the foundation walls. That will provide R 22. Then, we had interior walls (called frost walls) framed along the foundation walls, 7 inches away from the foam. When the cavity between the foam and the frost wall is filled with cellulose fiber insulation, at R 3.74 per inch, it will add 26.88, for a total R value of 48.88 for the foundation walls, with no thermal bridging. Not too shabby, considering that conventional builders will insulate to R 12, with a full thermal break at each stud. Here are some pictures:
The door opening in the MCNZH's basement. The foam is glued directly to the concrete (only 2.5 inches here, we ran out of foam, but we'll add more later), and the frost wall is framed out 7 inches away from the foam.
The window opening in the MCNZH's basement bedroom (opening still filled with plywood). Here you can see the full 5 inches of foam, with the frost wall framed 7 inches away.
Another view of the frost wall.
This foundation will provide very high energy-saving performance, and it was fairly economical. It should be a very comfortable place for someone to live.
(cross posted at raisingspaces.com)