Insulating under a Deck

Answer 1

We are adding a layer of insuation foam under our deck. Under that will be a layer of mesh to keep bugs from crawling through the deck floor. My father and I are arguing whether we should leave an "air pocket" of about 2 inches inbetween the deck surface and the insulation foam layers respectively. It's believed the trapped air will eventually heat up from the hot tub we're placing on the deck, and the heat will become trapped in this air pocket, which will keep the whole deck warm while keeping the cold air underneath from invading the surface.

Either way, I suggest the foam insulation.