Seeking creative ideas for building upon rock and mortar cellar

I live in Central Washington, with very hot dry summers and *usually* very snowy winters, sometimes 10ft total over the winter. Zone 5b or so according to agriculture science folks. I recently bought a 100 year old house that has a fieldstone rock and mortar cellar that's about 7.5-8 feet tall and has a two story stud framed house above it in great disrepair with multiple punched out walls and additions. The cellar stays about a constant 50 degrees and has the typical humid open ground feel. There's a storm cellar type of door leading up to ground level. On the uphill side of the house the rock wall is at ground level (not ideal, since the sill plate has rotted out and was replaced by previous owner), and on the downslope side the rock wall is about 2 feet above grade. The side with the door faces south, the uphill side faces a busy street, and the downhill side faces a creek. On the north side, the outlet plumbing to the septic tank is about 7 feet high on the rock wall. Electricity comes in on the uphill side to a panel that's in the cellar as well. Instead of trying to spend lots of $$ on repairing the house, I'm very inclined to make use of the subterranean thermal properties of the cellar and live somewhat underground. I like the idea of using cob and I like roundwood. Both of which materials I can find within 10 miles, and have experience using.

My rough concept currently is to deconstruct everything down to the foundation, build a short post and beam shed roof a few feet above the top of the foundation, infill the walls with cob,  and somehow insulate the roof ideally without fiberglass.

Big questions, though, are how would I get plumbing drains to travel downhill and out? Would I make a loft that has the bathroom and sink? Should I just make it an entire story on top of the foundation? I've heard cob can be hard to heat and might have condensation issues in cold climate? How steep do i need the roof to be to account for snowload, and if it's so short above the grade then won't it all pile up at the base of the roof? I'll likely dig a swale around the house to help with drainage, but there's minimal signs of any water seeping in to the cellar in past years which is good. And if I try to heat with a rocket mass heater or a wood stove, would you put that in the cellar or on the upper level?

Open to any and all ideas. I think there's ton's of potential to take advantage of a thick stone cellar especially in this climate. Eager to hear if others on here have suggestions. Thank you.

What's your regulatory environment?
Are you going to need code approval,building permits or  a certificate if occupancy?

Reguardless of any of that, a standing stick framed is a resource in and of itself.
Rather than removing it and rebuilding, why not reuse?

Since you are OK with a smaller living space, you could create a hyper insulated space above the cellar with strawbales.
The existing siding and walls would stay in place to protect the strawbale insulation.
You can finish the strawbales with earthen plaster.
The second floor and all the additions can become storeage, workshops, greenhouses or low mass thermal sunspaces (https://www.builditsolar.com/Projects/Sunspace/LowMassSunspace/TestsLowMassSunspace.htm#:~:text=Low%20mass%20sunspaces%20can%20be,design%20guidelines%20are%20not%20followed.)
You could also remove the additions and use the materials for your build.

Hi Sean,
I do worry about moisture and temp in a basement that was not built for underground living specifically. Having said that, I can suggest a couple of ideas for the insulation and plumbing.

For insulation, I am a fan of rockwool for ease of use. It installs similar to fiberglass, but has better insulative value. Rodents and bugs are not crazy about it. It's fireproof, and can get wet and have the same R-value after it dries out. It's made from slag and rock melted down and spun into batts. They also have some 4x8 sheets that are a little stiffer as a replacement for those 4x8 sheets of pink or blue foam.

For the drains. I think you either need the first floor for the height, or else use a pump. It's not uncommon around here if the septic is higher than the drains, for there to be a pump to get it into the tank. Unfortunately this means you need electricity for it to work.

Hi Shawn;
Nice find on your old farm house.
The basement/foundation looks rock solid.
The house looks like a 100-year-old added on to disaster.
I would remove the old house and build on your foundation.
I would build a stick framed well insulated single-story house with a steep pitch metal roof to shed the snow.
Of course, I would design this so my Batchbox RMH with bell would be centrally located in the center to keep me toasty warm looking out at 5-10' of snow piling up.

I see the long side faces south, which is good even if that is not the lowest ground. With the septic outlet 7' above the basement floor, your options are a sewage lift pump or keeping water appliances on the upper floor. I would go for the upper floor for simplicity, especially as the internal square footage (probably less than 15' x 32') in that basement is not very large and you would want more area for more than a tiny house.

I might excavate and take down a section at the southwest corner to say 4' above basement floor to allow a big passive window and "view" to the southwest to make it pleasant, maybe a floor opening to allow winter sun down the length of the south face to the basement from upper floor windows. As there is surely no insulation outside or under the basement, I would put down insulation and a new slab for thermal storage, and dig a bit all around outside and install waterproof insulation to a foot or so below grade and out a few feet, to minimize heat loss from the walls. If the existing main floor framing is okay, you might be able to keep 3/4 of it and just cut out and frame up an opening the length of the south wall.

The span across that structure is not too long and I think you could build a roof with minimal slope strong enough to bear snow load which would help insulate in winter. Maybe a low gable roof made with triangular rafters or trusses thicker in the middle to resist bending loads, with a flat ceiling which would allow view and solar windows without unnecessary height at the south wall open to below. Rafters thick enough for structure would allow enough depth for plenty of insulation.

A space with this configuration would be easy to heat with a mass heater centered in the basement, supplemented by passive solar.

When we bought the property where we lived now I was looking for something that had a place to live.  I would probably bought have that property if I had seen it.

If that house has been standing for 100 years there must be some good redeeming qualities.

Tearing down an existing house and starting over is a really big job.

Sean Eriksen wrote: On the uphill side of the house the rock wall is at ground level (not ideal, since the sill plate has rotted out and was replaced by previous owner), and on the downslope side the rock wall is about 2 feet above grade.

I think this is *really* important information. Judging from it and the picture, while working at ways to add some external insulation to the upper part of the basement, I would absolutely be looking for ways to change the slope and make sure that surface water had ways to flow around the building.

Options (I'd be combining a few of these)
1. well up-slope, consider gentle wide ditches that redirected the water across the slope to ideally somewhere more useful than your foundation! That could be as simple as rows of Yoeman subsoiler runs, but they might have to be refreshed every so often.
2. closer in, I'd consider simple dry-stacked rocks if you're in rock country that terrace the land, so that you can actually reverse the slope near to the east wall.  I've always been told that the number 1 rule that keeps houses dry is that the land should slope *away* from the house on all sides. The former owners hadn't read that rule and built a chicken coop and even worse, an attached run, with the north wall down slope, and yes, that sill plate rotted out! A concrete kneewall on that side would have helped, and might also be something to consider.

I think it's awesome that you're going to try to rehabilitate this building. Hopefully you're not in a big rush and can take the time to follow permaculture's first principle of "observe".