Easy Subfloor Prep For Hardwood

Subfloor Preparation: Why Is It Important?

When you’re trying to get the job done, subfloor preparation feels like it can slow the process down without providing any benefit. You may ask yourself, “Is it really noticeable if the floor is slightly out of level or not flat?” or “Do moisture measurements really need to be that spot on?”

You may be tempted to skip subfloor prep all together or give it half effort. However, a proper subfloor preparation process is crucial. Taking your time to prep the subfloor correctly ensures a smooth installation process and gives your customer a high quality floor.

Prepping Your Subfloor for Hardwood

Get the 6 important steps for subfloor prep shown in our how-to video “Prepping Your Subfloor for Hardwood”. Daniel, our Technical Director, shows the best tools, techniques and methods for getting the job done right.

What Tools You’ll Need

  • Your flooring
  • Manufacturer’s instructions for flooring (You can find our installation instructions here)
  • Thermo hygrometer (We recommend the AcuRite 00613, sold at our RW Supply+Design locations)
  • Moisture meter (We recommend the Lignomat SDM, sold at our RW Supply+Design locations)
  • Laser level OR box level (to record flatness/levelness)
  • Tape measurer
  • Pencil
  • Paper or phone note’s app to record moisture readings (or use our installation checklist)
  • Vacuum

STEP ONE: Read the Instructions

We know, it seems obvious, but it’s truly one of the most important steps in subfloor prep.

Becoming familiar with the manufacturer’s instructions will set you up for success. The manufacturer has tested the floor and knows what the product is designed to do, so above all trust their instructions. Industry guidelines often bow to the manufacturer’s instructions, so follow these rules. If you don’t, you could run into problems down the road with your floor.

For more installation resources, visit our Installation page on our website.

STEP TWO: Subfloor Prep
How do we know when the subfloor can be installed over?

How do you know when the subfloor is ready to be installed on?

First, make sure the house is at the right temperature and humidity levels for the flooring. Check for these three things specifically:

  • HVAC is installed and operational?
  • Moisture is within specifications for the flooring and subfloor?
  • Temperature is within specifications for the flooring and subfloor?

If you don’t know what these specifications should be, check the manufacturer’s recommendations.

Is the subfloor:

  • Clean?
  • Dry?
  • Structurally sound?
  • Flat?
acclimating wood floor
Two things to remember: acclimation is not a set time period and engineered and solid flooring have different requirements. Always check the manufacturer’s recommendations for how to properly acclimate the flooring.

STEP THREE: Acclimation Specifications

In this video, we used an engineered floor from Real Wood Floors.

Remember: engineered and solid products have different acclimation requirements for when and how you bring the flooring into the house.


  • Bring the flooring in early to acclimate to the temperature of the house.
  • DO NOT OPEN THE BOXES! Leave the flooring in the boxes as the flooring does not need to acclimate for moisture.


  • Bring the flooring in early. Let it acclimate for moisture and temperature in regards to the manufacturer’s instructions.
  • Cross stack the bundles or through out the house. This allows the flooring to receive proper airflow throughout the boards. Remove any plastic wrap from the flooring.
  • See our How to Acclimate Solid Hardwood guide for more information.
  • As an example of moisture and temperature specifications, these the instructions for our flooring are:
    • MOISTURE: 35% – 55% relative humidity in the house.
    • TEMPERATURE: The house is required to be between 60 degrees F and 80 degrees F.
Moisture meter on wood
Using a thermo hygrometer to measure your subfloor’s moisture content is a crucial step in subfloor prep.

STEP FOUR: Moisture Measurements

For this step you’ll need access to a thermo hygrometer. A thermal hygrometer will read temperature and humidity at the same time. Check the manufacturer’s instructions to find out what readings they require. For the product we used in the video, the manufacturer wanted the subfloor to read 13% or less moisture content, as well as read within 4% of the wood floor.

Next, you’ll use the moisture meter to read the subfloor’s moisture content. Here’s the steps:

  • Reset your meter so that it doesn’t have old measurements.
  • Set your moisture meter to the correct setting per manufacturer’s instructions.
  • Once reset, place it on the floor until it averages out and begins reading.
  • Record 20 readings per every 1,000 sqft.
  • Write these readings down as you take them – on paper, your phone’s notes app, or our installation checklist available to download for free.

As for what moisture meter to use when doing subfloor prep, we recommend the Lignomat SDM. Find a location near you and contact us to get one for your next job!

Man using level on subfloor
Use a level to check for peaks or valleys in your subflooring.

STEP FIVE: Checking for Flatness

After you take your moisture readings, check that the subfloor is at the correct flatness for the product. This is especially important with thinner floors as they tend to show more imperfections. For the product we use in the video, the manufacturer calls for a deviation of 3/16″ or less within a ten foot area, or 1/8″ or less within a six foot area.

To check for flatness, you can use either a laser level or a box level. As you can see in the video, we use a box level. Daniel moves around the floor with the box level looking for any gaps between the subfloor and the level. He measures those gaps, whether peaks or valleys in the floor, and marks them for later. Once they’re marked, sand your peaks down and fill in your valleys.

STEP SIX: Inspect & Clean the Subfloor

Our last step is to check for structural soundness and clean the subfloor for installation.

Go around the floor and check for loose boards, squeaks, and creaks. Screw or glue these wood panels down to solve those issues before placing flooring over them. Follow this up with a full sweep and vacuum of the floor.

Now you’re ready to install your flooring! Taking these steps may seem to slow the job down but ultimately it will give you a better quality floor.

We hope our video and article have been helpful tools for you to get the job done and get it done right!

Have other questions about flooring and the products you use?

Check out our resource page for more guides and our Youtube channel for more videos!