In building construction the subfloor is the layer(s) of flooring placed directly on the floor joists used for structural support of the actual flooring material. In modern construction this is typically a layer of plywood or particle board nailed, screwed, or glued to the floor joists. Depending on the floor type another layer maybe added onto this, typical examples being cement backing board for tile, padding, waterproofing, radiant heaters, or some combination of these items.