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Community and Q&A

Advantech floor over concrete

ES1972 | Posted in General Questions on

I’m building a small camp in northern Maine, approximately 16’x20′.  For a number of reasons, I decided to build on an insulated concrete slab on grade:  2″ of XPS foam over very well drained crushed stone, with a vapor barrier on top of that, then poured a haunched slab.  The perimeter haunch is about 12″ thick, and the center of the slab tapers up to about 6″ thick.  The vapor barrier wraps up the perimeter of the slab, and the entire perimeter is insulated with Rockwool.  All plumbing / drain penetrations were taped off to the foam and vapor barrier before the pour.  So I am pretty confident that the slab will not pull moisture from grade.

On top of the slab I put 2×4 sleepers, 16″ oc, with 1 1/2″ rockwool between them, and advantech subfloor over that.  The rationale was that since there is no radiant heat, that the insulation / wood might take the sting off the slab in winter, but I am realizing that I may have set myself up for trouble with this assembly, as I only let the slab dry out for a few weeks before putting the Advantech down.

My question is, assuming no new moisture will be getting into the concrete from outside, will the slab eventually dry through the sleepers/rockwool/Advantech assembly?  Or have I created a situation where the moisture will be trapped against it with no way to dry, eventually causing the advantech to rot from below.  The slab was poured in late September 2021, and the subfloor laid down a few weeks after that.  It has been dry and under cover for over a year, with no apparent problems, but I’d like to be sure before I put the finish floor down (probably this spring).

Thanks in advance!

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