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A friend and I are building a cabin in southern California. It doesn't snow often where it is located.

The cabin itself is setup on a post foundation and we are almost finished with the subfloor.

My question is, should we put a vapor barrier between the sub floor joists and the plywood sheets we put down? The front of the cabin is about 2 feet off the ground while the back of the cabin is about 6 feet off the ground.

If so, would something like Tyvek work?

cabin

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  • Is the cabin going to be conditioned (heated)?
    – Steven
    Feb 27, 2015 at 20:44
  • @Steven it'll have a pot belly stove in it for when we are there and the walls will be insulated, but no HVAC if that is what you mean.
    – Ronnie
    Feb 27, 2015 at 20:56
  • Do give some consideration to how you are going to keep animals out of the insulation, as well as keeping the insulation in place. And don't be stapling fiberglass batts up in there, (won't keep animals out, will trap moisture between two vapor barriers, falls out eventually anyway, bad all around.)
    – Ecnerwal
    Nov 21, 2022 at 16:27

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Tyvek is not a vapor barrier. Very specifically, it's a vapor transmitting air barrier.

A vapor barrier, if used, goes on the warm side of the assembly. So if it's more heating than cooling, put it under the plywood, or skip it and seal the seams of the plywood, which is a pretty good vapor barrier itself.

If it's more cooling than heating, underneath the framing.

Or skip it entirely and use cellulose insulation.

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  • we did end up skipping adding anything between the joists and subfloor.
    – Ronnie
    Nov 21, 2022 at 17:18

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