Can You Put a Couple of Plywood Sheets on Top of Each Other to Level the Floor?

Slight Issues

• If you're dealing with a subfloor that only has slight dips and valleys in it from the natural variations in wood, you can’t realistically use another sheet of plywood on top of the area to level it off. Instead, you should use a self-leveling compound to fill the voids and bring everything up to the height of the high spots in the subfloor. Adding another sheet of plywood just isn’t realistic because it will be too much to fill in the slight gaps.

Large Issues

• With larger floor variations, such as sections that just drop off, as in the case of a house that's settled incorrectly in soft ground, you can use plywood to build up the lower section of the floor. Sheets must be glued and screwed into each other, but you can build up the deepest part of the drop to around the height of the existing floor, then bridge the gap between the two with tapered pieces of plywood that are then covered over with self-leveling compound.

Nature of Plywood

• Plywood is meant to be installed in sheet format, as it was shipped from the manufacturer. Since it's nothing more than thin sheets of wood fibers bound together with resins and glues, if you try to cut it at a tapered angle you'll end up breaking the bond between layers, separating them along the tapered edge. This ruins the overall sheet of plywood along the area you just cut, and can create future problems if you don't glue it and screw it down securely.

Shimming

• The best method if you decide the floor needs to be shimmed is with trimmed-down pieces of the floor joist material adhered to the joists themselves. The plywood is then installed on top of the joists that have been leveled with the shims, allowing the finish surface of the plywood to be as level as you need it to be. You can use double sheets and place thin shims between the sheets as well, as long as the pieces are glued and screwed correctly.