I am building a detached workshop.  The shop will be heated and cooled.  I am having a slab poured with a 15mil vapor barrier over gravel. 

For the shop floor, I am putting down 2″ of Polyiso (Atlas Energy Shield XR), covered by two sheets of 3/4 Advantech, cross-laid to each other and the insulation board.  (This is the suggestion of Matt Risinger and others.) 

The assembly is for both insulation and standing comfort.  The Atlas board is supposedly better than the XPS boards like Foamular.  (The pink stuff.)

My question:  Should I put a dimple board under the floor assembly?  From what I have read, probably not.  I was thinking that with a dimple board or other membrane, the slab will be sandwiched between two layers and would not breath. Although I imagine that is basically what is happening with the Polyiso.

Thanks,