I was a watching a video today of a slab on grade construction at a new build PH in Ireland. Their buildup was radon barrier, concrete, and then what appeared to be 2 layers of 4″ thick polyiso-like sheets. The sheets were to be taped into aerated concrete blocks around the perimeter to maintain the thermal envelope. Seems as if in the US, the insulation layer is usually underneath the concrete. I know in a retro you can put foam on top of concrete, but anyone know why is it not typically done this way in new PH builds here, especially if you don’t want a finished concrete basement floor? I would install Advantech subfloor over the foam and then add radiant engineered wood flooring. However, I would put the foam under the concrete in the garage.