Building from scratch - uni diameter and material types

[Yurts_latvia]

There's some REALLY useful info here, regarding rafter dimensions, thanks all for sharing!


I suppose there should be some sort of calculation to get a rough idea of total bulk of wood needed for rafters for yurts of different dimensions, for different purposes (i.e. temporary or permanent, needing to bear a snow load or

insulation

, etc.)


Doing some calculations for the cross sections of rafters I could see that -



Bob's design up to 16ft, that can take heavy snow has rafters of 1875mm2



Yurtman's

camping yurts

, up to 20ft have rafters of 704mm2


Froit's 16ft yurts (presumably for permanent dwelling) have 66 rafters of 1024mm2



....but 6" x 2" sometimes used for permanent structures would be 7500mm2!! I suppose that would be for larger yurts.




Of course the quality and type of wood used is critical, and especially the number of rafters. Whereas a 16ft Mongolian yurt may use 66 pieces, modern designs may only 32.



The entire weight of the frame would be increased substantially if oak were used instead of softwood, perhaps demanding a stronger lattice?


Anyway, there's some more thoughts to ponder. It seems like there is plenty of wiggle room for adjusting dimensions according to ones needs.

[Yurtman]

There is wriggle room for

camping Yurts

, but not really for permenant yurts, especially if living in a wind or snow area. Local building regulations will have a big say in what you can and can’t do.
Quality of the wood is a big factor for permanent yurts. We are working on a prototype 20ft permanent yurt which was based on a design that was engineered. It called for 2x4 tight, Vertical Grain Douglas Fir (very expensive). The usual basic construction lumber is not strong enough. I expect if that was to be used, 2x6 would be needed.
I’ve always done camping yurts which are designed for lightweight portability, so permanent yurts are new for me.

[Yurts_latvia]

Thanks for your extra thoughts - and for highlighting how important the quality of the wood is.

[Bob Rowlands]

I made the lath and rafters of my three yurts with tight, straight grain, knot free 2x4 and 2x6 construction lumber. That's >VERY few< boards in the 8' stud bin at Depot or Lowes. I got four rafters out of a 2x6 btw.

Good as I built them, there's >no chance in hell< my yurts would pass any engineering standard in the U.S. Personal camping yurt use only. A yurt in the 20' /6meter range would need upscaled parts and I'm no engineer. Cool as that would be for big family get togethers, there's not a chance I'd ever make one for camping because they are too much work to tote around and assemble.

That said, trad Mongolian yurts have been built for centuries with zero engineering. The people that make them know they work and that's plenty good enough. if something goes wrong, nobody is gonna get sued, unlike here in the U.S. with sue happy lawyers looking to make a kill anyway they can.

The close spacing and incredible redundancy in lath and rafters of a Mongolian yurt means if something breaks the other framing easily takes the load. The typical Mongol yurt has about twice as many parts as one of my yurts. They are bombproof.

[Bob Rowlands]

As an aside here, the edit function on this site is great. I make alot of typos.