Subfloor Prep for Hardwood

Watch our video “Prepping Your Subfloor 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 the 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 detailed 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

Below we will flesh out the six important steps of subfloor prep shown in our newest how-to video “Prepping Your Subfloor for Hardwood”. Daniel, Technical Director at The Master’s Craft, will show you the best tools, techniques, and methods to get 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 TMC locations)
  • Moisture meter (We recommend the Lignomat SDM, sold at our TMC 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?

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

  1. HVAC is installed and running?
  2. Moisture is within specifications for the flooring and subfloor?
  3. Temperature is within specifications for the flooring and subfloor?

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

Secondly, go through this checklist for subfloor prep to make sure it’s ready for the flooring: Is the subfloor…

  1. Clean?
  2. Dry?
  3. Structurally sound?
  4. Flat?

STEP THREE: Acclimation Specifications

In this video, we’re working with an engineered product by Real Wood Floors. However, engineered and solid products have different acclimation processes in terms of when and how you bring the flooring into the house:

FOR ENGINEERED FLOORING:

  • 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.

FOR SOLID FLOORING:

  • Bring the flooring in early. Let it acclimate for moisture and temperature in regards to the manufacturer’s instructions.
  • Cross stack the bundles. This allows the flooring to receive proper airflow throughout the boards.
  • See our Acclimation 101 article for more information.

As an example of moisture and temperature specifications, these are the instructions given by the manufacturer for our flooring:

MOISTURE: 35% – 55% relative humidity in the house.

TEMPERATURE: The house is required to be between 60° and 80°.

STEP FOUR: Moisture Measurements

For this step you’ll need access to a thermal hygrometer. A thermal hygrometer will read temperature and humidity at the same time. Before you begin using it, make sure to reset it to avoid your measurements being mixed up with past measurements. Once it’s reset, place it on the floor and leave it until it averages out and begins reading.

Next you’ll want to take a moisture meter to the subfloor to read moisture content. Make sure you check your moisture meter and have it set to the correct setting. When you begin reading, you’ll want to record 20 readings per every 1,000 sqft. Write these readings down as you take them, either on paper, your phone’s notes app, or our installation checklist available for download on our website. As for what readings you’re looking for, check the manufacturer’s instructions. For the product we’re using, the manufacturer wants the subfloor to read 13% or less moisture content, as well as read within 4% of the wood floor.

As for what moisture meter to use when doing subfloor prep, the Master’s Craft recommends the Lignomat SDM. Find a Master’s Craft near you and contact us to get one for your next job!

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. As 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 with a full vacuum and sweep 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 any other flooring questions or just want to learn more about flooring and the products you use? Check out our resource page on our website for more articles and our Youtube channel for more videos!

For more installation tips, check out our article “Five Things You Should Do For Every Wood Floor Installation“!

Leave a Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.