The hub, tono, crown, dome... it has many names... is the keystone of the building. This is also the most difficult part to make. Some traditional yurts use bent wood, others heavy duty spoked wooden structures. I'm going for the latter because I like the way it looks.
The spokes, rafters, long straight pieces, fit into the hub and then attach to the top of the lattice wall. These are going to be fairly simple to make. Need strong, long, straight pieces of wood. They are usually square where they fit into hub (which has square holes just for such an occasion) and have a hole at the bottom end so that they can be tied to the rafters with a loop of string or something. Many modern day adaptations of yurts use metal brackets for one or both connections.
Most sources agree that for a 16 foot yurt, one should have a crown of 3 feet across. The number of rafters varies from 18 to 45, the length from 8 foot to 9'4", and the dimensions of the lumber 2x2 or there abouts. So this gives me the general range of what to expect for my yurt rafters.
The final aspect are the two upright supports. They probably aren't necessary except that they make setting up and taking down easier. Also, they look gorgeous and provide extra support for heavy snow.
This is what I would like my dome to look like (only in TARDIS blue):
I'm going with the traditional open top so that there is the choice to cook with an open fire, or later on add a woodstove or other cooker. There is a special piece of canvas that one pulls on top of the hole, either part way or all the way, to protect against terrible weather. The different sections can be filled in with plexi glass or other material later on, so I figure this design gives me the most flexibility.
Most sources say that it's put together with (forgive the spelling) mortis and tennen joins. I don't know how to do that... yet.
The outer ring appears to be made in three layers. The two outer layers and then a series of small blocks to create spaces for the rafters
How much to budget for the roof structure?
The rafters we can pretend we will use 8 foot, 2x4s ripped in half, a maximum of 44 rafters, so 22 2x4s, at $3.05 plus tax = about $80.
I really want to use 8 foot rafters, so I may need to increase the size of the crown in the center, but that's okay because it lets more light and air in.
When I think about making this hub, I get very heavy hearted. I feel like this is the part that is so far beyond my current skill set that I'll never manage it... I'll have the rest of the yurt built but this... but I know I must do it, so I will do it.
There is always plywood I suppose, cut the circles from that, then put something in between for the spokes to fit in. Plywood needs extra weatherproofing or it will delaminate. It could work, but not my first choice.
There is also this really interesting hub made at Tenderfoot Farm - part one, part two. It's several layers of wood, staggered and glued together then shaped into a circle, then the holes for the rafters drilled into the side. There are no center supports.
For my yurt, there should be some bits of wood left over from making other parts of the yurt, that we can use to make the crown. With a bit of thinking and creativity it can be quite strong and won't cost too much extra. But we also need glue, drill bits, wear and tear on the tools, travel expenses to get materials, screws... so I'm going to budget the crown at $50.
The uprights... Let's say $20 as a very vague guess.
That's $150 for the roof structure, roundup to include tax and unexpected extras because something always comes up and we will say a budget of $200 for the roof structure.
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