Do You Need to Put Plywood Under Floors?

Tile and Stone

• Two of the most difficult types of finish floor materials to install are tile and natural stone. They both require significant amounts of support from the floor beneath so that deflection doesn’t pop tiles off the floor. Plywood is the only rated subfloor that is acceptable for use with tile and natural stone installations, and double sheets must be used.

Carpet

• Deflection isn’t as much of an issue with carpet as it is with tile, but carpet floors still need some form of a subfloor in place to provide a foundation layer. It also serves as something for the carpet padding to adhere to and for the tack strips to secure to around the perimeter of the room. Once everything is in place the carpet may be installed and the support beneath is provided by plywood.

Hardwood

• If hardwood is going to be nailed down, it needs a type of material that can stand up to the force of nails and screws as well as provide sufficient density to lock the screws and nails in place. Plywood is the only subfloor that can offer that outside of high-quality OSB. Because plywood is layered in sheets, it grabs the screws and nails on multiple levels, providing superior support for hardwood floors.

Floating

• Laminate floors or non-nailed hardwood floors are installed using the floating method. A layer of padding is put down on top of the subfloor and then the flooring is installed on top of the padding, but not actually nailed down to any surface. Instead, the floor literally floats on top of the padding. In this case you can use OSB rather than plywood, as the finish material is never in contact with the subfloor and doesn't need a bond of any kind.