YurterRT, thanks for the comment.
For those reading this and wanting the link, the yurt plan and build is here:
clan yama kaminari-home
On the front page, left side top box, click on 'make it'. Then, scroll to the bottom and click on 'yurt/ger construction'.
12', 14', and 16' yurt build plan in full accurate detail.
That is a very good plan. I built the 14' and 16' versions and it is a fine plan for sure.
You could easily expand that plan to a bigger size, I'd say to about 20', by using 1x4s for rafters, instead of 1x3s. Also, block the ring with spacers made from 4x4, not 2-1x3s cut and beveled. Widen the plywood ring to 34" and make the flange 6" wide. I drilled pilot holes and glued and screwed (3" plated) the ring segments with poly urethane construction adhesive, which is waterproof.
Also, if you want an 18' or 20' yurt you need a 'custom' rafter pattern not in the Kaminari plan.
To determine 'exact' lay out of rafter pattern, you absolutely must draw a full size cross section of the yurt roof, wall to ring, on your garage floor, and mark your 1x4 in place on that section. No math, and totally foolproof. You lay the rafter stock on the pattern, and mark it. I did this with my 15'9" yurt.
Don't be afraid, it is actually very simple.
Here's how. Snap a line on the garage floor about 12' long. That line represents the 'top of wall' height, from one side of the yurt, to the opposite wall. You omnly need 12' because it is only necessary to draw a half section to get a rafter layout.
Mark a spot on that line at one edge. That represents the top of the wall, where the rafter sits. From that point, measure in half the width of your perspective yurt diameter. That is the radius of your yurt. The focal point of the yurt ring, the exact center of it looking through the hole from down below, is perpendicular to the radius spot.
Measure up 3' to the bottom of the yurt ring, and draw a half section of it ON THAT RADIUS line. The section is simply 3/4" ply, 3.5" block spacer, and another 3/4" ply. That is the thickness of the ring, in section. If your ring is 34" wide, you are drawing the section 17" towards the wall side on the wall height line you first snapped.
Again, make the bottom of the ring parallel with the wall line, and perpendicular to the focal point. I do suggest 3' elevation above wall heigthbased on experience with this kaminari yurt. That puts the bottom of the ring about 8' up from the ground.
Once you have the section of the yurt ring drawn out, lay a 1x4 on the outside wall to rafter point, and on its spot into the yurt ring. Transfer all marks. You have the pitch, length, plumb and level cuts, all in exact position.
VOILA! An 'exact fit' custom rafter guaranteed with no math calculations necessary.
Note, I wouldn't go bigger than 20' diameter with this yurt in snow country, UNLESS you install bagana supports under the ring. On my 16'er, no support in necessary and I have had perhaps 1.5' of pretty wet snow up there. Also use a 1/4" cable, minimum. Nothing wrong with 5/16ths either for added
.
Have fun.