Floating subfloor over concrete stack
Project: Full bathroom remodel (60 sq/ft) on a 96 yr old Seattle (4c climate) slab-on-grade home.
Where we were: At some point a toilet and bathtub were installed and part of the slab was broken up but never backfilled (!). A poorly executed sleeper system with 2x4s, drywall (!), insulation batts (!), subfloor and linoleum has been removed.
Where we are: Room currently concrete slab, dirt, and studs. Not a basement.
Where we’re going: Matt Risinger did a floating system (Halo Interra GPS boards over concrete with 2 layers of Advantech subflooring). Having a hard time tracking down GPS but have heard of using XPS (higher PSI anyway) for this stack.
Once I backfill the concrete over the plumbing and then use a self leveling compound if needed over the full floor, my plan is to seal the concrete (overkill?), and then place XPS directly on the concrete and on top of that 2 layers of Advantech subflooring screwed to each other (but not through the foam board or concrete).
Am I missing anything? I don’t believe I’d need a layer Visqueen with the stack described. Or do I? And where in the layering would it go?
Thank,
Josh
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Replies
It's important to have a vapor retarder to keep moisture in the ground from making its way up into the floor system and the indoor air. A sealer on the concrete might work, and the rigid foam will help, but with the low cost and high durability and efficacy of poly sheeting (Visqueen, e.g.), I would use that.
Thanks, Michael. That makes sense.