Floating Home Floor System- Vapor Barrier?

[andyho]

Requesting advice re: vapor barrier under a floating home. We are in Seattle. The floating home is on a log raft. The ultimate wet crawlspace...We have "stringer beams" laid perpendicular across the logs at 4 feet on center. Then above that we are building a joist system of 2 X 6. However, we want the bottom of the joist/insulation space to be protected from RODENTS. So, we are proposing a (treated) plywood bottom to the joist system. The plywood would sit directly on the frame of stringer beams, joists on top of the plywood base (with insulation in between them), plywood subfloor on top of the joists. Where, Should, and What would we install as a VAPOR BARRIER and could you please recommend an insulation material? Thanks.

[ThingOfBeauty]

What an interesting home!

I would think a "raft" of XPS polystyrene would be ideal. Treated plywood, layers of XPS, joists now laid flat and screwed through the XPS into the stringer beams. Fill between joists with more foam if you like.

Probably more than you want to spend though.