Technical Design Question, Wooden walls still need Tension band?

[CrawDaddy]

Hi all,

I'm trying to design a yurt-like structure, in the sense that it is roundish in shape, and was hoping someone might have some engineering expertise on the matter. I'm considering making it approx 12' diameter on the interior, with solid 2x4 walls that can be insulated. I'm considering making it 12-sided rather than a true circle, to make it easier to install standard doors and windows mainly, and I've also considered making the walls tapered, ala Bill Copperthwaite's design.

My question is:

TENSION BAND
If I made the walls plumb, and they were framed with 4x4 posts, and they had a double top plate that overlapped the seams, would that be strong enough to resist the outward roof thrust or would I still need a tension band? I've thought of either cutting the top plate out of plywood or 2x12 or whatever is required to get the radius, and possibly laminating the two layers together for extra strength? And possibly some kind of metal bracket or fastener to connect the posts to the top plate. The roof is obviously pretty small and light at 12' diameter, and it will be built up from the inside out: 2xrafters, t&G decking, rigid foam

insulation

, metal roofing. Basically I'm wondering if the strength of the solid wood framed walls, locked together with the top plate as well as horizontal blocking in the walls (which will serve as nailers for the vertical wood siding) is enough to counter the roof thrust? Or if I should just throw a cable in there for extra security?

If I tapered the walls, I suspect I would need the cable regardless. Has anyone out there built a taperd wall yurt like Bill Copperthwaite has designed and promoted and have any feedback on it?


Thanks!