Can you answer some more questions on crawlspace insulation?

Follow up question to your answer (below):Q. Correct, there is about four feet between the ground and the floor that is exposed on two sides. For batts, what R value should I use? I was thinking R-40. Should the vapour barrier be applied from the outside (up and underneath the rafters followed by insulation, then plywood or chicken wire) or, can it be laid over top of the plywood from the inside. There will be underpad and carpet laid over top. Someone suggested this could cause the plywood floor to rot. Also, should I use house wrap over the wood that will be used to secure the insulation in place between the rafters outside.A. "I am going to assume that the deck was built on piers. In other words, the floor of the addition sits at least a foot above ground level, and air can travel freely underneath this area. The most viable option, in this case, would be the use of a vapor barrier on the warm side of the insulation (above the insulation) and the use of fiberglass batts between the joists. In all likelihood, some type of material will be required to prevent the insulation from falling. Chicken wire is acceptable, except in the areas where vermin will attempt to get into the insulation and make an nest. In which case, very fine mesh, or thin plywood should be used. The plastic that is there now is acting like a vapor barrier on the wrong side of the insulation."