Need Advice on Tiny Home Stone Foundation

Good evening, I'm planning to build my first (tiny) round house and I'm looking into sustainable materials, and seeing as houses begin with the foundation and there's a quarry nearby, I'm leaning towards a stone foundation. The house and its walls will be under 5 meters in diameter. At the quarry I saw many large stones, well over a ton which I'd love to incorporate into the footing of the house, but I'm not sure if I need something like gravel or stones underneath the boulders for drainage or stability. I'm in a northern climate with copious rainfall, so I will dig a primary drainage ~40cm around the edge of the house. I'm thinking I can build the footing out of smaller boulders, upon which I can cob. My question is - Am I forgetting something vital?

Hello Maruf,    I would definitely put stone under the foundation not just for drainage but also for frost heave mitigation.
Lots of info if you search something like: "rubble trench foundation".
Also, a book that I have really enjoyed reading again and again is The Hand Sculpted House by Ianto Evans, Michael Smith and Linda Smiley.
May be worth checking out as it covers a lot of information from one source.
Good luck!

Hi Maruf - welcome to permies!

I've heard in really wet climates, they recommend flashing between the rock knee-wall and the cob so that the moisture doesn't wick up in the rainy season. I agree with Gerry that The Hand Sculpted House is a lovely book.

Thanks for the advice you two, I got my hands on a copy of the book and I'll be devouring it.

Jay you mentioned 'flashing', a new term for me, I deduce you mean a moisture barrier. Following the advice from The Cob Builder's Handbook, he says moisture barriers go against natural building as they prevent the house from breathing. My climate's not a jungle, and I'd prefer to forego using synthetic material if something like a French Drain would suffice. In your opinions, are moisture barriers really that necessary?  

"Flashing" is a term we use for the layer of metal surrounding a chimney to stop the rain/snow from sneaking water in around it. I've also heard it used for the metal used instead of roofing shingles in what I would call a "valley" in a roof for the same reason. (we've got several "valleys" in our roof and I would never design a roof needing one if it was at all possible to avoid in a climate such as mine!!!)

My understanding of cob buildings is that when indoor humidity is high, it is absorbed by the cob and when it is low, it is given off, which makes living in the building more comfortable. Yes, a "vapor barrier" (paint can be a vapor barrier - which is why cob building strive for natural, "breathable" finishes) would stop this from happening and that would be a bad thing.

The "flashing" I referred to is horizontal between the rock foundation and the cob. Water is neat stuff and it can move vertically against gravity (just ask any tree!) The ground where I live is much wetter in the winter than the volume of water made up of the "humidity" in the house. Yes, you want to also do everything you can to keep the foundation as dry as possible by directing water away from it, but a place on Vancouver Island called O.U.R. Eco-village has done a lot of work to get cob buildings and strawbale buildings approved by the authorities and somewhere in that process, I was led to believe that this horizontal waterproof layer was recommended. It would have been punctured by something like rebar to make sure that the building stayed tied to the foundation as we're also in an earthquake zone. I think the rational was that if too much moisture soaked up from the ground into the cob, then the cob would be too wet to have the indoor humidity absorbing affect it is supposed to be good at.

I have never built with cob, but as my son's girlfriend said last night, she "can't believe the engineering shit I've absorbed just from being around engineers". Hopefully one of our cob experts will chip in. This is climate specific - my sister runs a humidifier in the winter in Ontario - we run a dehumidifier! Painted drywall simply can't absorb the quantities of water in the air when we get a month of rain (let alone 3 months which has happened some winters.)

I can only speak from my experience. my current house probably built in civil war era has a stone foundation. the house is twisted, nothing is level anywhere.
there are some building experts that can direct you to how to make a solid foundation, I would not skimp on a crating a solid foundation.

Maruf,   Chapter 10 "Drainage and Foundations" in the Hand Sculpted House talks a lot about what your looking for. It even brings up what to do in earthquake areas for extra stability.

Daniel Ray has documented a wonderful journey of building his own home here: balecob-home-earthbag-foundation-building
Perhaps there is some information there that could help also.

Gerry Parent wrote:

Daniel Ray has documented a wonderful journey of building his own home here: balecob-home-earthbag-foundation-building
Perhaps there is some information there that could help also.

The O.U.R.Ecovillage I mentioned above has also used earth bags with some cement in the mix for foundations or at least parts of foundations, so that is a good thing to explore as part of your planning.

Thank you everyone, I've read up on everything about the stone foundation, however, I've one more question about the actual drainage. I'm trying to forego plastic and underneath the rubble trenches I see people use pipes. Could I hypothetically lay down a layer of clay on a decline to send the water down and stack the rocks in the center to form a cavity to let the water pass?

Secondly, the frostline here in Lithuania is 1.2 meters. I'm not on a hillside so where should the water collect once it drains off? Do I dig a cistern in the ground or what?

A channel is all the water needs to flow. Nothing fancy. Rocks would work fine for this application. Pipes just make it easier and faster but certainly not imperative.

If there were a need to store your water, a cistern could be used. If your just interested in keeping it away from the house, then just have it dissipated into the ground via a french drain.
Directing it towards gardens, trees or other plants could also be considered.

How much rain or snow can you get in a short time? How sandy or clayey is your soil around the house? If it is well drained and you don't often get heavy rains, a french drain type of infiltration may work fine combined with surfaces sloped away from the house in all directions; if not, you need to slope the drain trench to a lower place where it can flow out to the surface.

A few layers of moderate sized stones that keep big gaps between them, covered with progressively smaller stone and gravel down to sand at the top, will keep the drainage path clear for you.

The land is super sandy with little clay, so unless I'm inspired enough to dig a dry well or cistern, I think I'd get away with just a French drain.

Regarding a barrier to prevent silt from collecting, how necessary is the barrier, if I were to say make the drain wider? The walls of my home will be at least 62cm at the base, so how much wider does the drain need to go out? Could I get away with making the width at the surface wider than at the bottom? If so, how much?

I understand you are past this point now, but for posterity, I would say that you could just do the layers of progressively smaller stone/gravel/sand in a trench as wide as you need to dig to be able to work in it. As long as the drainage quantity is not unreasonable (your sandy soil would say you will have little problem), any rock-filled trench you can stand in should be fine. The layers of smaller gravel and sand will keep dirt from sifting down and blocking the drainage, so you would not need an artificial barrier material. If your soil is very sandy, you might want the layers of smaller material on the sides as well as on top.