How to Lay Plywood Underlayment

Most floors consist of three layers: a subfloor, usually of tongue-and-groove plywood, set directly over the floor joists (the horizontal support beams under the floor); an underlayment, generally of straight-edged plywood, to provide extra strength to the subfloor and a working base for the finish flooring; and then your top flooring of hardwood, carpeting or other material. Laying the subfloor correctly is crucial because it has to provide a smooth, strong surface for your finish flooring.

Things You'll Need

• Plywood, enough to cover the floor (1/2 inch)
• Galvanized wood screws (1 1/2 inch)
• Sawhorses
• Tape measure
• T-square
• Circular saw

Instructions

1. Get the subfloor completely clean and dry. Walk over it to ensure there are no loose spots. If there are, sink screws to tighten it.

2. Set your first piece of plywood in one corner of the floor, running in the opposite direction to that of the sheets that were used for the subfloor. Make sure none of the seams of the plywood line up with the seams of the subfloor. (If they do, move the plywood two feet over along the wall.)

3. Sink 1 1/2 inch galvanized wood screws every foot or so throughout the plywood piece, starting about two inches in from the edges and covering the whole board. Sink the screw heads so they're just below the surface.

4. Lay your next pieces of plywood in the same fashion, butting them up against each other. Lay them in rows, staggering the rows so there are no four-way intersections between the boards. Make sure none of the plywood seams line up with the subfloor seams.

5. Cut the boards as needed for the end spaces along the walls. Cut them by marking the distance on the board, extending the line across the board with your T-square. Set the piece on sawhorses and make the cut using your circular saw.

Tips & Warnings

• Wear eye protection when making your cuts.

References

• Underlayment