Hi, I bought a 1950s red-brick house in Alambama, and am wondering two things. First, should I insulate under the floorboards (in the crawl space). I put down some plastic (4mm) on the ground already, but it's very hot and humid here. WOuld I need plastic above or below the insulation too? Second, how do I know if I have enough insulation in my walls, and how would I go about insulating them if I don't want to rip out the sheetrock.