Building a net zero energy home, as all my readers know, requires construction of an airtight, super insulated building envelope. Walls are, of course, a key component of the building envelope. I found that the least-expensive option for my house was a fourteen-inch thick double 2 x 4 wall insulated with spray foam and cellulose. This was far cheaper than SIPs and ICFs and resulted in almost no bridging loss.
Once the subflooring was laid, we began to frame the double 2 x 4 walls. The outer 2 x 4 wall was framed first, sheathed with ½-inch OSB, then tilted into place.
Here are two sections of the outer 2 x 4 walls, braced to prevent them from collapsing.
Once the outer wall was in place, we framed up the inner 2 x 4 wall. We did not stagger the 2 x 4s as is sometimes the case because I sprayed the inside surface of the inner wall with an inch and a half of polyiso and because the inner and outer studs are separated by a 7-inch gap that was filled with dense- packed cellulose.