I’d love some feedback on this plan. I’m building a single-storey fully insulated shed. My plan tries to balance four aspects:

1) Potentially moveable — building on top of 6×6 PT skids.
2) Sturdy — 2×8 floor framing with 16″oc joists.
3) Well insulated — using 3-inches of Comfortboard 80 under the joists to minimize thermal bridging.
4) Solo-build as far as possible

I won’t have enough space under the structure to work from below. I’m height constrained so I don’t have the option of increasing that crawlspace. 

From the bottom up, I’m planning:

– solid concrete blocks on gravel
– 6×6 PT skids
– 1/2 PT ply 
– 3-inches of Comfortboard 80 (two layers as I can only get 1.5 inch)
– 2×8 PT floor joists (Comfortbatt fluffy filling the voids)
– 1/2 inch ply subfloor
– wood flooring

I’m planning to put long structural screws through sheathing plywood and comfortboard and into the joists. I can’t do that from below so I will be building in three inverted sections. Then flip those sections over and fasten on the pairs of outer 2x boards that make up the 12′ beams.

My working plan is to make the outer parts of the beam from ripped down 2×12. So they drop all the way to the outer sheathing ply. Bearing directly on top of the skids beneath. I could make all three layers of those lengthwise beams full height but… I figure this approach saves some weight in the sections I need to flip and reduces the amount of comfortboard coverage I need to sacrifice.

Specific questions I have: 

– Plans I’ve found on FHB and elsewhere typically show skids inset by a foot or so. Am I missing something important by having the skids align with the outside edge of my floor? (wall sheathing, comfortboard, rainscreen and siding will add ~5 inches overhang outside the edge of the skids)

– Does this look like a reasonable trade off between sturdiness and thermal efficiency? I could potentially make it so only the outer board in the lengthwise beam drops down to the sheathing. That would reduce by bridging area by half but I’m not confident that’s structurally sound.

General feedback appreciated too. Thank you.