Home Addition

The time has come to throw some thoughts out to the knowledge commons and see what sticks. Hard to pick a forum to place this one, it is being added to a tiny house, it will have natural and contemporary building methods, earth bermed, stone work, cob, etc.

A little -longish- story and some context.
I live in a small home I built myself using local lumber from a time in my career where I ran a local sawmill. It's a nice place and we (wife and I) learned much about building and living in small spaces. We have been in this house about 6~ish years. We have a detached bathhouse and some other hand-built outbuildings scattered about.
My work experience in general has been running specialty heavy equipment of various types. The last few years has been underground... I like facilitating moving water. Plenty of my close friends are journeymen level skilled tradesmen, as am I.

I have a sentimental attachment to building with rock, so the addition will have a rock foundation and at least a partial wall. I built a small crane trailer that dumps and can pick decent sized rocks fairly easily. We have good access to excavation/compaction equipment and are looking to invest into our own excavator for a variety of reasons, this project being one.

After a couple kids and years, we are ready for a little more space. The addition will be roughly 16'x32' and a portion will, out of necessity, be buried in a hillside. The deepest cut will be about 5' then tapering to about 2'. No uphill view, so the usual water problems exist.

Some rough drafts ideas, use large (2'+) rocks and concrete to form a footing. I have plenty of surplus slotted 6" HDPE pipe to throw behind it for some drainage. As well as sloping everything to daylight and backfilling with aggregate.
I have a few rolls of pond liner and conveyor belt material to toss behind the buried portion of the walls as well.  I am figuring foam board behind the wall itself, then liner, then conveyor belt to help protect the liner. Probably roll on some kind of toxic gick water stuff before the foam board too.

Once to grade, use slip form method to build up the foundation walls a few feet above dirt line. I figure I will be bored of stacking, hauling and dealing with rocks by then and probably set a concrete bond beam. Then switch to some other material for the remainder of the wall.

There is an adobe block maker within striking distance of my place, so that is appealing, or use a slip form cob using machinery to make it. I have played with machinery mixed cob a bit myself over the years and there is good local knowledge. Unless the rock work goes all the way up... which is possible but not likely.
Deep concrete footings with surplus steel pipe and I-beam for pole barn style framing to support the roof... all that material is on-hand already.

I will update this with more thoughts and context as time goes, but figured it'd be good to get something out there for discussion.