2 layers iso vs 1 layer EPS/1 Layer Iso

Why is it that with 2 layers of staggered insulation, iso is always used in both layers and not just one? Can you safely use a layer of EPS and a layer of iso to save money?>>>

I have used both Mike.

Now you have me doubting my memory though, LOL. Time for some more Ginko Biloba I guess.

Ed>>>

Ed,

Are you sure that the stuff you used wasn't Expanded, instead of Extruded?

Made of lots of tiny white beads that could be flaked off if you rubbed it hard enough, or very easily if you broke off a section.>>>

I used to pick it up from some place in Waukegan Illinois and I think the name was PolyFoam Packers, but that is over 10 years ago and probably longer than that.

Ed>>>

Ed,

I suppose it can come in any color they want to add, but I'll admit, I've never seen anything except Dow's blue and OC's pink........... or whoever might make pink now.

Who makes a white board?>>>

Mike,

Extruded Poly Styrene also comes in white.

There can be no Class C Fire Rating with EPS unless a firestop product is installed under the EPS to the decking, such as gypsum board.

Ed>>>

Jed, EPS is polystyrene. Expanded Poly Styrene (white "bead board"), but I've also heard people use to mean Extruded Polystyrene (the blue or pink stuff). >>>

The one obvious thing is the Fire rating.....There are limitations with Polystyrene over combustible decks and Steel Decks. Without doing the research, I am fairly sure that FM will not accept Polystyrene directly over any substrate other than concrete. I am also fairly sure that UL. will require a recover board for fire spread from the topside.>>>