Identification

• Plywood underlayment is a sheet of wood that comes in various thicknesses, including 0.75 inch. The most commonly used is the 0.25 inch thick plywood underlayment. Floor joists are long, wood girders that provide support for the entire flooring construct.
  
  

Features

• Plywood underlayment does not need to be separated from the floor joists, but need to be directly attached to them. The strong connection between the joist and underlayment will bear the weight of the final flooring choice, from carpet to hardwood floors.
  
  

Considerations

• Care must be taken when attaching the underlayment to the floor joist. "Floor Covering Installer" suggests using underlayment staples for the best construction results. Also, make sure that none of the plywood installed has water damage, as this can result in weak spots over time.