Rafter Drama

[Dan R-M]

The rafters in my Spirit Mountain yurt are a tenuous construct, for sure. They are meant to be pinned into the center ring and notched (with locking screw) onto the cable. Were the Simpson A21's fastening the rafters to the ring "factory", or done by the first owner to add a little confidence?



Who knows. But the first real windstorm we got this summer knocked down a few that hadn't gotten their A21's on yet. It was easy to put all but one back up. That one was one of two that are secured over the door.
Here's an opportunity to ask a question, rhetorically at this point, of what you do when the rafters have to attach over the door and can't sit on the cable. I didn't want to simply screw them down, 'cause I figured they'd need more flexibility. So I came up with something a little bit complicated but very functional. Or it would have been if I had secured the rafter at the ring, too.
Here's the dilly: I put two ~2x2" pieces on either side of where the rafter would sit, then drilled a hole through them with the rafter in place, and put an extra rafter pin through to hold it. The result is that the rafter can flex up and down, but if it happens to fall out of the center ring then the pin stays put in the door end and the rafter splits as leverage is put on the stubborn pin. And, like I said, I never would have known about that unfortunate feature if I'd secured the stupid thing at the ring in the first place.




I left the yurt without this rafter for a while, then last weekend we got a whole lot of wind, and that brought down the other door rafter. So, in anticipation of a storm tomorrow I figured I'd better not have a two-rafter gap, and I fixed them both, complete with A21's.

Jafo, I recommend another Forum Topic: Fixing the Damn Thing.

 

[Jafo]

That is a pretty cool design as long as those blocks hold up to the jarring you describe. You may want to consider digging around your local hardware store and find a metal version of what you have there. Maybe an L shaped bracket with a slot in the middle? Maybe something like this:

And then use a nut and bolt. I still can't believe the issues you are having with those rafters. Wow! I mean, my rafters have not budged an inch since I put them up so it is just wild to think how different those SMY yurts are!

 

[bss]

I was definitely thinking metal too jafo. Perhaps eyebolts that screw right into the top of the door jamb on each side of the rafter, with 4" bolts and nuts thru to secure them.

Definitely a clever idea though. The uselessness (for lack of a better term) of the rafters over the doors has always bugged me a bit.

 

[Dan R-M]

Hmmm... Funny how the easiest solution is not often the one that comes first to my mind. If/When the pin and blocks fail, I'll go for the angles. Thanks for the reflections, guys!

 

[HawaiiYurts]

Meant to comment on this a while back. I'm betting that the brackets are after market. Usually door rafters are screwed in place from the underside of the door header. they have enough flex with that method. But your idea is good!

Every yurt is that much better when rafters are secured at the ring as well as along the cable, and the cable to the lattice walls. High winds, earthquakes, etc. put the structure to the test, and the more you can secure those points, the more you can secure the yurt.

 

[Tree Bones]

I know that some of my posts might be a little late but can still help.

I use a similar block system (much smaller with no pin) at the rafter to door where the cable is still attached to the rafter and the rafter is screwed down to the top of the door frame.

My first experiments with yurt construction (20 years ago)I used similar Simpson metal brackets to connect rafters to the hub and found they had to much flex and was a week point leading to collapse under wind and snow. Since then the best results I found have been from a very solid connection at the hub so any flexing is better at the wall connection. It is important to have a secure connection at the rafter and wall but they still seem to flex. If you use a snow load support system at the bottom of the rafters this flexing will be less. When it comes to wind the canvas takes up most of the flexing.