I have an older home in Nebraska. The attic is very large and we use it as storage. It has pull down stairs that I keep insulated with a rigid foam board box that I made. I have R13 insulation between the floor joists (ceiling joist of the upstairs rooms) since they are 2x4s. I have 3 layers of fiberglass in the areas that are closest to the roof since it is too low for storage. (gable roof). I am considering laying foam board insulation down on the plywood floor where the storage is, and then covering that with a thin layer of plywood, so I could still walk on it and still have storage. I think I could get r10 to r15 with the foam board, and with the r13 fiberglass in between the joists, have about r23 to r28. Any comments?