Vapor Control for Tile Floor on Sleepers
I’m in the Pacific Northwest. Previous owner had converted a garage to a living space. I’ve only done some poking around but they appear to have done a fairly reasonable job. 6 mil poly on the concrete, sill plate foam, untreated 2*4s (standing 4″ tall), and then 1/2″ plywood. On top of that is underlay and carpet. The 4″ space underneath the floor is not ventilated or vented in any way. I need to do some more investigation but so far, it looks nice and dry.
We are going to be taking out the carpet, adding some reinforcement to the floor, then Ditra uncoupling membrane, and then tile.
My concern is that perhaps the plywood/carpet is currently allowing a way out for any moisture in that subfloor area and I might trap it in if I go with tile. That space will be trapped between two vapor barriers.
1) Does that sound like a reasonable concern? Does the plywood/underlay/carpet actually provide much of a path for vapor?
2) If yes, what would you propose as a solution? Ideally something that doesn’t involve tearing out the current plywood because that’s basically a full rebuild. It’s a little tricky because the sleepers means that the floor is actually a large collection of smaller compartments.
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