Im in the process of planning out completion of the attic floor in my 1895 house. Right now it has joists with several areas of plywood or fiberboard nailed in place for access to some areas. Nothing is consistent. The rest of the floors in the house have the original wooden planks, with decorative wooden flooring on them, usually oak and birch. I am wondering what is considered the proper base material and thickness, keeping in mind that a another layer of wood flooring will eventually be placed on it. As this is the third floor, am I wrong to be keeping in mind the weight of the various thicknesses of flooring as well? Thanks!