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Prepping a Plywood Subfloor for Hardwood or Laminate Flooring

Prepping a plywood subfloor is crucial for hardwood or laminate floors that last. We show you how.

Introduction

It’s what you don’t see that is the most important part of a beautiful, long-lasting hardwood or laminate floor: A well-prepared subfloor is key to lasting hardwoods and laminates.

First, calculate the room’s square footage to find out how much flooring you’ll need to buy. Do this by multiplying the room’s length by its width. If you have an irregularly shaped room, divide the room into smaller squares and rectangles, calculate the square footage of each smaller area and add them all together. When you buy, add 10 percent to the total. This allowance covers imprecise math, irregular pieces and cutting mistakes.

Before you begin, read the flooring manufacturer’s instructions carefully. Know and follow all local building codes. If you don’t feel comfortable, Lowe’s installation services may be the easiest way to handle your hardwood or laminate installation.

These instructions apply to preparing a plywood subfloor. If you are installing on concrete, reference How to Prep A Concrete Subfloor.

Clean the Subfloor

Step 1

rolling old carpet pad away from the subfloor

Pull up the existing flooring. Also, using a pry bar and hammer, remove baseboards to create an expansion gap – a space that allows the new flooring to expand from heat and moisture.

Caution

Old flooring may contain asbestos. If you are unsure of safe removal and disposal processes, consult a professional.

Step 2

stack of flooring beside door casing

Check that your moisture barrier, underlayment and plank fit under your door casing and door. If they don’t fit, cut 1/16 inch to 1/8- inch off the casing and check again.

Step 3

sander on plywood subfloor

If you're gluing the new flooring to the subfloor, use a sander to remove paint, oil, wax, adhesives, sealers or other material. Then, thoroughly vacuum off dust and debris. 

Good to Know

Nail-down or floating floors may be installed over existing vinyl as long as it is no more than two layers thick. Thoroughly vacuum the existing floor and use a long level and tape measure to ensure the subfloor is level within 3/16 inch for every 10 feet. Sand any high spots and fill the low spots with leveling compound. 

Caution

A floating floor (laminate or locking hardwood) should NOT be installed over a wood subfloor adhered to a concrete slab.

Step 4

moisture meter in use with readout on display

Check the moisture level of the subflooring using a moisture meter. Compare the results against the manufacturer’s specifications for moisture limits. If you have a plywood subfloor over a concrete slab, check the moisture level of both floors. 

Step 5

electric drill over plywood

Finally, repair any loose or squeaky boards by screwing them securely into the floor joists

Prepare the Subfloor

Step 1

roll over underlayment over plywood subfloor

Unroll the underlayment and moisture barrier, if needed, in long strips, joining each row with tape, being careful not to overlap the edges. Leave it long at each end of the room – you’ll trim the length after the floor is installed.

Good to Know

Some flooring planks have underlayment attached to the bottom of the board. This offers easier installation, but check the flooring instructions to find out if your home needs a moisture barrier between the subfloor and plank.

Step 2

illustration of flooring running perpendicular to floor joists

Structural guidelines require that some flooring be installed perpendicular to the floor joists.  If the new floor will run parallel to the room's length and floor joists, you need to reinforce the subfloor with an additional piece of plywood. 

Create a Guide

Mark a guideline on your subfloor to run a square floor. 

Step 1

blue chalkline X in the middle of a floor

Mark the center of each wall on the subfloor. Snap a chalk line between marks to form a cross in the center of the room. 

Step 2

illustrated floor with allowance for expansion gap marked

Measure the distance between the center point and the starting wall. Now, subtract the manufacturer’s expansion gap from the measurement to create your guideline measurement. 

Step 3

man marking guide with chalkline

Using the new figure, measure along the parallel centerline to each end of the starting wall and make a mark. Snap a line connecting each new mark to form a guideline for starting the floor. 

Install Your New Floor

You’re almost ready to start installing your new floor. Remember that flooring requires at least 72 hours to acclimate to your home’s temperature and humidity levels prior to installation. Check the manufacturer’s instructions for specifics on acclimation periods. 

For more on installation, reference How To Install an Engineered Hardwood Floor or How to Install A Solid Hardwood Floor.