Building a platform - thoughts.

[Aaron Harris]

Hello!

I'm looking at building a 30' yurt. Before I commit to my footings, here's the situation. I'm trying to minimize the number of footers I need to dig and pour/slipform: I'm down to 12 in my design.

It's rocky granite mountainside (beech) forest, though with a reasonable amount of loamy topsoil, 4' frost line. I figure I'll do some slipform stone and cement/mortar to speed the footers up.

I checked out the maximum permissible spans for various weights and lumber dimensions, and since 15' was too far, I went with an octagon instead of a hexagon. (It would have been nice to get away with 7 piers)

I'm also planning on snow load.

30' yurt. 4 12' sistered 2x12s for perimeter beams, 2x8s or 2x6s for the joists spanning up to 9'. I'm not in love with the joist layout, but I am pretty sold on the octagon perimeter and 4 center piers.

Are there any obvious problems with my design in the attached images?

Thoughts?

[hierony]

Heh, almost looks like a yurt roof (crown ring and roof poles). Neat sketch. How do you intend to precisely cut/attach all your joists?

If you make the interior square sides the same length as the exterior octagon side length, you can then put girders across--four big ones (maybe sets of 2x8's nailed together but check the tables). Just draw four lines across your piers, ending up with an upper trapezoid, a middle rectangle, and a lower trapezoid. Then frame across those--should give you something like 7' spans or such while still retaining 12 piers.

I checked the photo section, and the first photo I found matching this was Dennishl's. There's probably some others, too. And alternate designs.

Hope that helps! Let me know if it didn't make sense.

[Bob Rowlands]

That is definitely an ingenius design. The joists need blocking though. To solve that problem I'd box up a square 2x frame that rest atop the center beams. Make it 2-2X thick, or 3". Size it so all the joists radiating from the center square bear on the beams below by 3". Frame the outermost box first, the one the joists butt into. Toenail it to the beam below. As you start installing the joists, lay a joist in place and mark the angle. Cut the joist. Let it run wild at the outside. Nail through the box joist into each joist as you go. There will be no room to nail later and obviously no joists will be hangered except those in the center.

Sister the second 2x to the first on the inside. Hanger the middle joists within the square in standard practice. If this were mine I would also block between the joists at the outside beam as well. Just lay the block stock on top where it goes to get the angles and mark them all at once. Sheath the top with 3/4 t&g plywood.

If you have a heavy stove planned, note where it sits and deal with the framing appropriately. Have fun and good luck.