Poly-iso under garage concrete with radiant heat, good idea?

[m@c nchz]

My dad's building a new garage and wants to put radiant heat in the floor. A local guy's got some "seconds" poly-iso foam board for a really good price.

So,can you actually use poly-iso under a concrete slab, especially with heated floors? Or is there some reason you can't or shouldn't?

Any insights or warnings from those who've done it (or know better!) would be super helpful. Thanks!

 

[Trev4rr]

You can use poly iso, but it's not ideal under slabs, it doesn't handle moisture well and can lose the R value when it gets damp...and which of course slabs love to do, so, left to me XPS is the better call for below grade or under concrete