Hello Zelig,
It was actually from Yves of
that I learned about the strawbale platforms--he's posted on the forums about his setup. I emailed him for more details--I'll share what I learned/he said (he's more verbose in french). I also have a few photos of my setup in my
album. I started with a rectangularish platform which didn't work well, then rebuilt it circular to fit under the yurt (much better).
Yes, I am using the strawbales--I like them because it will be completely movable and I won't leave gravel or cement piers or holes behind, just a bare spot (the original meaning of 'yurt'). It also keeps the yurt above groundlevel, so no worries about water or snow getting inside. Of course, don't setup in a low spot with poor drainage where water will collect into the bales. Yves said he didn't have problems with moisture in the bales at all, that they looked new when taken up after two years.
Levelness: I was lucky to have an old asphalt pad already level for me--except for a tree root or two pushing up the asphalt in one corner. The bales did not smooth out the root bumps--I would recommend making your 'base' as level & smooth as possible/reasonable (<1" deviations). Yves suggested putting down a layer of gravel and then an 'earth sheet'/plastic layer to really do things right, but he didn't have the time during his setup. I didn't use anything under my bales (except asphalt pad).
Arrangement of bales is important--the yurt on top protects the bales underneath from weather. Anything sticking out will get water/snow on it and potentially mold. I made this mistake initially--I arranged my bales as a square inside the yurt circumference with the outermost bales sticking out (plus my OSB sheets stuck out initially, too). Then it rained, they got wet and the bales molded some
![Frown](https://www.yurtforum.com/forums/images/smilies/frown.gif)
Below is what I'd make from scratch--I think my setup actually has two or three circular layers instead of just one though.
Start by putting two bales in the middle with a rod/stick to define your center; use a rope/board to scratch the outer circumference. Tie a rope/cord the circumference length--paracord would be sufficient & cheap; ratchet straps are overkill. Knee/kick the outer ring of bales to fit the curvature & use the cord to hold your circumference. Then stack outwards from the center until you can't get anymore whole bales inside your outer ring--fill the gaps by stuffing with portions of bales. Make sure everything is level--adjust with bale flakes as need be.
Plastic sheeting--I originally had 8 mil plastic between the bales & OSB. I was planning on tucking it up inside the canvas under the lower rope once I cut the OSB circular, but it caught water before I got it setup that way. A couple spots on the OSB started to mold, plus a fair number of bales underneath got water through holes poked by straw/screws and started to mold, too
![EEK!](https://www.yurtforum.com/forums/images/smilies/eek.gif)
Once I noticed this, I rebuilt circular and omitted the plastic sheeting.
Platform--Yves used 1/2" plywood sheets, I used 3/4" T&G OSB (11.5 sheets for my 20' ger). A little thicker would probably be good to reduce flex. Plywood is probably better than OSB (better water resistance/less edge swelling, less outgassing). I tried using screws though the T&G joint to hold everything together but it didn't work. Similar to Yves's setup, I ended up using 1x3 (furring strip) underneath all the joints to screw into to hold everything together.
This picture shows one way to do this--perpindicular pieces would be required if not using T&G. Cutting the platform close to circular is essential (it'll catch water and cause problems otherwise).
Drip edge/border lip/skirt--with a traditional yurt like Groovy's, you'll want to have a drip edge/border lip/platform skirt. It'll keep the lattice on the platform in *very* strong winds; with the canvas & vapor barrier outside it/insulation & liner & lattice inside it'll help seal up the yurt; and also gives an exact diameter for setup purposes. I initially ignored this, but am going to install one shortly. I'm not sure what Yves used--maybe thin plywood? I'm thinking of using 1/4" tempered hardboard cut ~6" tall in ~2' long sections, screwed into the 3/4" thickness of the OSB.
As for critters (mice/insects), Yves didn't have any problems but he also had a cat. When I was rebuilding everything circular after the water problems, I did notice earthworms under the moldy bales. I'll probably be moving my yurt here come June, so I can report back on what's underneath :P I also have a design for a modular T&G board (pine or cedar) platform in place of the OSB, but need to test it first. If you really wanted to seal everything up, you could stucco the outermost side of the straw bales and glue/seal all the plywood joints. With just the canvas (no liner, no insulation, not a great seal between the canvas/platform edge but the crown ring covered) the yurt'll warm up with my 15-25 kbtu/hr propane heater in ~40 minutes.
Oh, each bale was $2.75 each, ~1'x3'x1.5' direct from farmer. I think I got wheat straw but there may have been some barley straw, too.
Let me know if you have anymore questions.