How to Install a Plywood Underlayment

Plywood underlayment is essential to the performance and appearance of a number of types of finished flooring materials that require installation on top of a very smooth, level base for best results. Properly installed plywood underlayment, in addition to providing that smooth surface, according to APA, the Engineered Wood Association, also adds “strength, appropriate stiffness and load resistance to flooring systems.”

Step 1

Measure the sub-floor to determine the total square feet of plywood required for the application.  As noted by the Canada Forest Products Information Portal, plywood is available in 4-by-8, 4-by-9 and 4-by-10 foot sizes, depending on the thickness selected.

Step 2

Select and purchase the recommended type of plywood based on the specific type of finished flooring that will be installed over it.  As mentioned at the Online Tips website, the grade of plywood required varies based on the kind of finished flooring.

Rosboro Company, a lumber supplier, offers a handy quick selection guide reference for choosing plywood type based on finished flooring application. 

Step 3

Start in a corner when beginning underlayment installation and then work from there across the sub-floor.  Avoid overlapping the seams in the sub-floor by cutting the sheets of plywood as necessary so that smoothness will not be compromised.

The iflooringinfocom website recommends the use of 1-inch deck screws or ring-shanked nails to attach the plywood sheets to the sub-floor. 

Step 4

Fasten each sheet of plywood by counter-sinking a screw or nail “every 2 inches along the edge and every four inches along the remainder of the sheet” as recommended by Halex Corporation, a flooring installation manufacturer.  Halex also notes that plywood panels should be “lightly butted” together, not forced tightly together.

A 1/4- to 1/2-inch expansion gap should be left between the edges of the plywood and the walls. 

Step 5

Mix and apply some flooring patching compound to the seams and to the countersunk heads of all nails or screws after completing the attachment of the underlayment to the sub-floor.  Scrape off any excess patching compound with a putty knife after it has dried thoroughly and then use a belt sander to sand the surface smooth.

Clean the underlayment of all sanding dust before beginning finished flooring installation. 

Things You Will Need

  • Tape measure
  • Circular saw
  • Saber or coping saw
  • Power screwdriver or nail gun
  • Putty knife
  • Belt sander
  • 1-inch deck screws or ring-shanked nails
  • Plywood underlayment sheets
  • Patching compound

About the Author

Based in Arlington, Texas, Larry Darter has been writing articles on a broad range of topics including building and construction, outdoor recreation and personal finance since 2009. His articles have appeared on Suite101 and Associated Content. In addition, Darter writes content regularly on assignment for private clients. He holds a Bachelor of Science in accounting from the University of Central Oklahoma.