I got both layers of OSB cut and fitted today. The bottom layer is thicker and is fitted to the frame. It would be more than enough floor all by itself. Then I cut a thinner layer of OSB offset from the first. Tomorrow I will cut the Foamular insulation layer that will go in between them, and start adding the ring around the edge. I was able to use only four 4×8′ sheets to make each layer by re-using the smaller off-cuts to make the final two small corner triangles. We are rapidly approaching Yurt Time!
I was forced to cut into the frame just a bit to get the circle right. In Sketchup I think I had maybe 1/2″ of clearance, but the wonkiness of the corner pieces and their strange angles must have thrown things off a bit. To prevent that from happening in the future, the center single 2×4 in the corner pieces would need to be at least an inch shorter. I didn’t cut into any fasteners, so the strength shouldn’t be affected. It was already just about as solid as the trailer I’m in now with only the first layer screwed on. Once the second layer is on, it you could do sumo on top of it. I’m still intending to do three 45 degree tie downs to hold it centered, but they’re total overkill.