Much progress has been made! With some alternations to my original diagram.
Our yurt has been delivered and we are working away at the foundation. I have zero masonry experience, but inspired by an image of a stone yurt foundation I decided to go for it. I'll add the picture I'm talking about below. it seemed many people were interested in this foundation option, but every time I saw someone hoping to replicate it, someone would ask how the yurt would be anchored. Interested myself I searched for anyone who had been able to safely attach the yurt to a foundation like this but came up short. I wanted to share my efforts to do this for anyone else searching for the same thing. Again, I do not have masonry or much construction experience. I do not know how well this will work but I am just going to try my best and keep you guys updated.
After removing the sod from the area where our yurt will be going, we started digging a trench for the stem wall. We live in Maine where the frost line is 4ft down. Having already done a lot of digging for planting this past spring, having to hand dig our well line and leach field, and sitting over a ledge that comes and goes, we opted for a less deep solution for the trench. This trench is 28 inches deep where the original grade was highest. This is at the front of the yurt, in the back the grade is much lower. The trench was filled in first as a rubble trench on a 1-2% slope; for this we laid out heavy duty landscape fabric to prevent silt from clogging the drainage, we put down 2 inches of clean crushed rock, put a 4 inch corrugated pipe in, and coved that with a minimum of 2 inches of crushed rock over the top. The fabric was folded over the rock. In the midst of this a big storm passed through and water filled our trench. we had not yet dug the outlet area of the last piece of pipe, so we had to do our best to drain the trench. I was pleased to see that the rain water collected well at the bottom of our trench, the slope seemed perfect.
We then spread granite stone dust over drainage and tamped it down. We have a lot of stone dust on the ground after having a well put in so it was convenient to use and packed incredibly well. I used as much as I needed to create a level base to build on. We are required to use a minimum of 16 inches of below grade insulation for this to be considered a 'frost protected foundation'. Our codes here are kind of wonky, we have so few people in our town we aren't required to follow much, but heat loss is a rule that's a must. So that's how I ended up with the rigid foam board. All 16 inches of the foam will be back filled around outside the foundation for the foundation to be considered frost protected, as the foam has to be below grade. We put the foam up and starting laying the base layer of rock.
We have two large field stone piles available on this land, so stone was a semi convenient and free option for us. Having no masonry experience my methods were basically to use big boy rocks in the bottom of the trench. I try to place stones so the slope into the wall rather than away, I do my best to not allow joints in the rocks to overlap, the further a rock reaches into the wall the better. I use a lot of small rocks stuck into the mortar as hearting stones. I use a 5 gallon bucket for my mortar mixture. The mix is made up of a heaping bucket of stone dust (in place of mason sand, our stone dust is fairly gritty), half a bucket of Portland cement, a quarter bucket of hydrated lime, and about two gallons of water.
I am finally getting to the top of the foam board on one half of the stem wall. The yurt is 30' across and will sit on top of the rock wall, it will not overhang the insulation as I first sketched out. Right now I am placing rebar into the stem wall. We have bent the rebar into a soft 'V' shape (trying to not hurt the rebars strength the best we could) with an L on each leg. At the bottom of the 'V' shape we will be hooking 1/4" galvanized steel wire, tying the wire with cable clamps. This wire will run up the yurt wall, hidden in the layers of canvas and insulation, up to the top of the yurt wall where it will connect probably to our 2x6 studs that sit beneath each rafter. I felt this wire was fitting for the yurt as the top of the wall is already held together by a 1/4" wire that comes with the yurt kit. This is my solution to anchoring the yurt to this foundation. I am also going to set up an anchoring system with the dome, that I'll explain and show later.
The stem wall will continue above the current insulation, probably about 12 inches above grade. I am hoping the weight of another foot of rock holding the rebar down will help with the anchoring.
The inside of this stem wall is going to be filled with road base that we will tamp down. This will build the floor up and make a level base to build our earthen floor on.
I'm planning on setting a piece of rebar like this under a wall post every 6+ feet or so, it will act as an anchor for the yurt. Our yurt and I think many others come with a plywood band that wraps around your foundation. this band is meant to be bolted to your lattice walls and then screwed to your foundation. This is what normally anchors the yurt, but people also 'normally' build a wooden deck as a foundation. A wooden deck would have taken an insane amount of wood for this and with wood prices so high, also cost nearly 20 grand. There is some wood on our land that we do plan to use in the future for building, but we'd have no trees left if I cut enough wood for an endeavor like that. The best solution I could come up with to anchor the building and be able to build with stone was to install the rebar. I'll share some images of how I am connecting the yurt to the rebar when we put the yurt up.
I am currently considered a couple more predicaments however. I'll attach a diagram I quickly drew to help explain, but essentially I am questioning 3 things...
1. I was planning on mortaring stone tiles to the top of the stem wall to provide a flat surface for the yurt walls to sit on, will I have any problems with water wicking up the stone stem wall into these tiles and rotting away at the wood frame sitting on them?
2. How high above grade should the foundation be to prevent water, that may make its way through the stone wall and under my floor, from flooding my earthen floor? We are on a high dry field, I thought a minimum of 6 inches above grade before adding insulation and the earthen floor...
3. I've created a cold bridge here, where there is a gap of no insulation along the wall between the yurts insulated canvas and the foam board below grade. I do not want a cold bridge for efficiency purposes, and also because my foundation must stay warm in order to be 'frost protected'. How can I break this cold bridge? I can only think to cover the stone with more foam but I'd really like to minimize the foam used, and see at least some of the rock wall we have worked so hard on.
Hi Amber, Far from being a pro here but will give your questions a go.
1) With the height of your stem wall in the diagram and a good drainage system, I can't see water wicking as being a problem. If anything, splashing water from the roof will be the biggest thing - If the ground where the drip line from the roof is not able to absorb the waters impact, it will splash back up on the stem wall and canvas. Canvas in particular can get dirty looking and even moldy during wet seasons.
2) A good drainage system, road base, vapour barrier and foam insulation....I think you've done a pretty good job!
3) I agree, we definitely want to see that beautiful rock! Can you insulate this section on the inside instead? Perhaps with rock wool or perlite?
I wonder if I could wrap a line of haybales around the base of the yurt, and cover them with something to keep them dry, for the winter. Then when the weather starts to warm up, I could slowly use up the hay or straw for other purposes.
The only problem I could think of would be the bales might end up decomposing on the ground if they aren't kept dry enough...or maybe mice might take a liking to it?..hmm..
Working at it slowly with this heat, but we finally got the plywood band together today. The plan is to finish the top layers of rock over the weekend and shimmy the band up into place. We are essentially using the band as a form to make sure our circle is 30 ft across and that the yurt will fit inside. My hope is that Sunday night the foundation will be done and drying, so we can start putting the yurt up Thursday.
In the meantime we will continue bringing in road base to raise the floor up in preparation for the earthen floor. We have brought in about 250 wheel barrow loads of gravel so far. A long way to go for sure, but it is good to finally see something there besides rocks rocks rocks
Do you guys ever find that something you think will take a week takes you 3 weeks? We are on our third lap around the circle, the circumference is just under 95'. I think after today we will be 1/3 the way around with this top layer, which is turning out to use a lot more rock than I expected. Here are some progress pics.
We had calculated how much rock it would take, approximately, but we ended up building the foundation up higher than we originally planned. We have finally finished the rock, aside from a small opening we left to be able to bring loads of road base in. Now we have attached pieces of wood on the top of the stone wall. This will serve as an outer ring of floor, and a surface to mount the yurt's plywood band too.
Today we are transporting the yurt to the land, and continuing to bring in road base. Hoping to put the yurt up this weekend provided it isn't raining too hard...and I need to somehow find scaffolding or something...
Next week it'll be on to the earthen floor.
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