The subfloor is the lowest layer of flooring that sits directly on top of the joists. Once the flooring is installed the subfloor is hidden underneath. Because it is a difficult to access position, making changes to a subfloor is a fairly expensive and difficult task. Most subfloors remain the way they were built during the construction of the home.

 

The subfloor should not be confused with the underlayment. The underlayment is what is placed between the subfloor and the floor surface to ensure the best performance of the flooring and to keep moisture and noise out. While subflooring is usually standard and uniform throughout the home, the type of underlayment used can vary from room to room depending on the type of flooring being installed.

 

Cement board is the underlayment used when installing tile flooring. It is placed over the plywood or concrete surface and holds the tiles together.

 

If you are installing wood flooring, plywood is the best underlayment for you. Any plywood between 1/2″ and 3/4″ and A/C rated will work for both solid and engineered hardwood flooring.

 

Laminate can also be installed over a plywood subfloor. However, laminate is a fairly thin floor, so adding thin plywood as a secondary subfloor is recommended, especially if you are installing laminate flooring in an older home. Subfloors in older homes are often no thicker than ½” of plywood, as opposed to the ¾” thick layers in newer buildings. Because laminate is so thin, it can easily show imperfections. To protect your floor from gouges and dents, you should install an underlayment, preferably foam or cork padding to provide some flexibility and help smooth out subfloor imperfections.

 

The main danger of tile floors is cracking. Old, infected joists can be a cause of fractures. Installing a stable plywood subfloor will help prevent any movement that can lead to damage. The underlayment should also be non-sagging and sturdy to support the tile floor properly. Cement board can be installed directly over the plywood layer.