More work on the octagon required.

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I still have to add horizontal, 2x4s struts around the base of the walls at obs. floor level. An attachment surface for flashing is required. Not to mention the grooved plywood cladding. Which is intended to stiffen the whole structure thanks to skin effect. The building presently sways an inch or more at obs. floor level compared with the stationary pier if I put some effort into it. The building has a very low frequency. Which will drop still further with the weight of the dome on top.

I'm hoping the 12mm [½"] plywood skin will firm things up. Failing that I'll need diagonal braces with some very odd compound miters at each end. Though I could brace internally between horizontal braces and joists with nothing more than a bird's mouth at each end. I have plenty of 2x4s stacked and awaiting just such a purpose. The problem is avoiding it touching the huge pyramidal pier. Or blocking easy access to an already difficult building shape. There is loads of headroom inside but an octagon is as bad as a cylinder in having no useful corners for storage [or bracing.]

It would so tempting, even now, to take the whole lot down and put a 14' calf dome over a simple square building! The main problem is that it would require an even bigger raised ground area for the building. Probably double the original quantity of self stabilizing sand & gravel would be needed. The original soil level is well over 3' down and falling away from the parking area right in front of the building.

The last lot of sand & gravel had to be shoveled and barrowed manually in from the drive over 30 yards away. For all the bragging rights such foolishness makes little sense. The contractor who promised to come and move it for us had lost interest when I rang him to say that over 20 tons [10 cu.meters] of sand had just been delivered. It was lucky I didn't ask for it to be dumped in the middle of the drive! It took my wife and I several days [as septuagenarians] to shift it all to the building site.

The irony is that the very same contractors work for the local authority on drainage projects. They have been working in the field nearby on several occasions since then. Always using a mini-excavator and several young "onlookers" to move as much soil in a whole morning, as would take me less than an hour with a shovel while working alone. Nice work if you can get it!
  

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