jwp, I read several books on the subject, then gave it my own twist. It's just an experiment so judge it accordingly .......
***** Darn it, several pictures of slipform construction were lost during the server move. *****
Slipforming is a messy process that gets too much mortar in some places and not enough in others. You have to knock off the excess mortor (preferably while it is only a few hours old), point the joints, and wash the concrete stains off the rocks.
The rock in this area is basalt and nothing but basalt. It's brown and boring but, like I say, it looks like it belongs here. I will probably haul in some pretty rocks from the Salmon River to accent doorways, etc.
The 2" foam is not so great; 4" would be better, but the foam is very expensive and the 16" wall doesn't have room for 4" of foam anyway (the 16" wall was originally intended to be cordwood, not stone). If I had to do it over again, I would make it 18" wide, with 4" foam.
My logic goes like this:
-- I wanted stone inside and out, for fire resistance, and because it looks appropriate for a mountain cabin.
-- I wanted thermal inertia on the interior side of the insulation. Most stone houses place the thermal inertia on the exterior side of the insulation, where it does no good.
-- I want it to be earthquake resistant. There's remesh in both walls, and there will be rebar at corners and at halfway points. The two walls are tied together with 14 gauge wire on 12" centers. There will probably be additional ties at critical points.
-- I want it to be strong enough and wide enough to support a 16" cordwood wall on the second story, if I decide to go that route (I keep changing my mind).