I have a room built on an above grade slab, the roof of a tuck-under garage. I want to install a glued 3/8″ plywood prefinished free floating floor over the existing 9″ tiles. Instead of the standard roll underlayment I thought of using 1/2″ polyisocyanurate foam board with reflective foil face for greater R value. As an alternative what about 1/2″ foam sheathing with film facing? Will either of these withstand compression and is the off gas of the polyisocyanurate a consideration? jiminmin
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After considering my own question, I think it would be necessary to use 1/2" plywood sleepers 12" o/c for the 3/8" flooring. But then I wonder if I could use good, old fashioned 1/2" fiberboard sheathing, "Biltrite", glued to the floor in full sheets without sleepers as this material does not seem to compress much? If this is possible what would I use between the flooring and the Biltrite as a vapor barrier, plastic,tar paper? jiminminn
Has anyone floated a floor over extruded foam without sleepers? It comes in 15,25, 40, and 60 PSI. And I was hoping 60 might be enough to support a floor under normal loads( no pianos).
I did something like this before I knew I was doing. It was for my home office about 10 years ago. In general it has worked ok, but I made some mistakes.
I used stock home horror store blueboard which I think is the 25 psi. But remember 25 psi is 3600 lb/sf.
The problem is concentrated loads. I used some realy crappy 3 ply plywood (3/8" ??) which I held down with a tapcons. Then I tried to screw some 1/4" laun over it and then lay some vinyl tiles. The plywood had a problem holding the scews and some of them worked loose under the tiles.
If I was doing it again and I wanted a true floating floor I would use t&g sub-floor material. And glue it to the foam to make sure that it does not shift.
Then you could nail your finish floor to it.
My dilemma is getting max-R value with minimun height increase. My most recent idea would be to seal the slab with oil based paint. Then glue 3/4" 60 PSI extruded foam sheets to the slab without sleepers. Over this I would glue 3/16" luan ply underlayment( if necessary?) Next the manufacturer's recommended underlayment and finally the prefinished, glued, 3/8" plywood floating floor. Does seem feasible?