Insulated subfloor

[theoldwizard1]

My nephew bought a fire station !

He is contemplating installing radiant in-floor heat by placing a subfloor over the existing concrete floor (10"-12" slab, no vapor barrier or insulation underneath). For the most part this will be one big (2,00-2,500 sq ft) heating zone. The commercially available pre-made panels, like DRiCore have woefully inadequate insulation (1.5-3.0 R) and they are expensive.

He was think about laying down 1"-2" of polyiso foil faced rigid foam baord and then 3/4" OSB on top. I have read that polyiso should not be used for this because any moisture that gets under the OSB will be absorbed by the polyiso and can cause mold. True of false

Other suggestions ?

 

[terabitdan]

Congrats to your nephew. That should be an interesting project.

I have read on GreenBuildingAdvisors.com that XPS is much better than Polyiso for this since it does not absorb moisture.


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[ssdave]

Terabitdan is right on. Do not use polisocyanoacrylate foam under a floor. Use 2" of XPS for a R value of 10. That's quite adequate for a floor. Put 6 mil plastic under the foam to insure that moisture doesn't wick up from the concrete.

 

[ard]

So after the foam and OSB, where is he planning on putting the radiant heat?