A. This can be done, but I would not recommend it. Movement of anything against polystyrene foam creates a terrible squeaking noise. Remember the last time a foam cooler rubbed against something in the back of your truck?
Except in the most extreme northern climates, insulating a floor over a crawlspace is questionable because you lose some of the cooling advantage. In the summer, there is considerable cooling by heat radiating from the floor to the soil.
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