I’m constructing a tree-house for my family and am about to close in the framed single-level “house” structure with sheathing. It’s traditional 2×4 16OC walls with a (forthcoming) shed roof. The structure is flush with the edges of the elevated 2×8 PT deck on which it sits on the three back sides and has 3/4″ PT ply as subfloor in that area. I’m planning on using zip sheathing since we do get a fair amount of rain and I’d like to make the structure last as long as possible and be water-free inside (and just don’t want to deal with housewrap up in a tree). Two questions:

1) How far down should I bring the sheathing? I don’t think I should leave the subfloor ply edges exposed, but I’d also like to keep the look of the “deck platform” on which the house sits. Is there there minimum distance I can bring it down over the PT 2x8s in order to add some lift strength or should I just overlap the subfloor edge and stop overthinking it.

2) The front of the structure has an open “deck” area topped with 5/4 planks which stands a bit higher than the 3/4″ subfloor beneath the framing. I’ll obviously have to stop short of the floor in the front with sheathing, but is there a straightforward way to protect the subfloor (flashing on the face of the framing, etc)?

Thanks.
Dan