It is important to acclimate hardwood flooring to its new living environment properly but the question most often asked is for how long? Most will say put in the house and let it sit for a week, and you should be set. Wrong. That scenario is incorrect and making that mistake can prove to be very costly or cause you to live with a hardwood floor that does not meet your expectation.

Proper acclimation is not a period of time but rather a set of conditions.  The National Wood Flooring Association (NWFA) describes acclimation as the“process of conditioning wood flooring to the environment in which it is expected to perform.”

To understand this, let’s think about how living trees prosper in nature and how they act after becoming hardwood flooring. Water enters a tree through its roots, and it travels upward through the inner bark using a capillary system that acts like little straws.  These straws make wood hygroscopic, which means it readily absorbs and releases moisture.  That does not change just because the tree is harvested, kiln-dried and installed in your home.

If you look at the end of a piece of kiln-dried hardwood flooring, you will see the capillary system is still there just waiting for moisture to suck up.

Where does excessive moisture come from?


The NWFA and most hardwood flooring manufacturers say that a hardwood floor should be installed and maintained with a relative humidity of 35 to 55 percent.

Water Vapor Emissions

If your home is built over a crawl space, the ground in that area needs to be covered with 6 mil black plastic to prevent moisture from escaping into your home.


Not enough moisture will result in shrinkage, and too much moisture will result in expansion.  Shrinkage will result in gaps between boards and expansion will lead to cupping.

Job Site Preparation

Wood flooring installation should always be one of the final steps of any construction project. Before wood flooring is delivered to the job site, make sure it is ready for the wood, and the wood is ready for the job site. Wet elements including plaster and paint should be dry before the wood is delivered.

Levon Karapetyan, CEO of Northern California’s prestigious Artex Flooring Inc., shared how he prepares a job site for the delivery of wood flooring.

“Before we receive a shipment of wood flooring, we monitor the job site to make sure the relative humidity complies with recommended standards, which is 35 to 60 percent. We also make sure the doors, windows, and HVAC are installed and functioning. We check the perimeter of the house for any suspicious areas that need to be brought to the contractor’s attention.

Communication at this point between the flooring contractor and the general contractor is essential. Don’t buckle under pressure from the contractor or homeowner if the above conditions have not been met. They may say, ‘Don’t worry about it, just put the floor in now, we’re running behind schedule.’

They may not care now, but they will care six months or one year down the road when they have flooring problems,and those problems will be your problems to fix.Levon believes it’s important to educate your clients.

“It’s always good practice to keep your clients informed. You need to give them as much information as possible to ensure the success of their wood flooring.”

Levon holds his ground if conditions aren’t suitable, even if builders or clients insist the flooring gets installed.  “If the moisture content is high on the concrete or on the job site, we tell the contractor we have to follow certain steps to bring relative moisture and humidity down with dehumidification or HVAC. Then we’ll come back and check again to make sure the moisture content is in regulation according to suitable moisture content standards. If it is, we will then bring in the wood flooring.”

The Last Step

“We always make sure the wet trades are completed before we bring the flooring in. We won’t deliver the material while they are still working. After we have taken all precautions and know the job site is ready, we will bring the wood flooring in and let it sit for one to two weeks depending on the situation, and then we will proceed with our installation,” he explains.

It’s always better to delay bringing in wood flooring materials if the walls were just painted or the subfloor isn’t completely dry, says Levon. Wood flooring is hygroscopic, meaning it will naturally absorb moisture and change dimension. Wood will expand when it retains moisture and become smaller when it loses moisture.

Wood Flooring Moisture Measurement Guidelines

Solid strip wood flooring, less than 76 mm wide, that has been acclimated properly, will not have more than a 4 percent moisture content difference between the flooring and the subfloor. For flooring that is more than 76 mm wide, there should never be more than a 2 percent moisture content difference. Wider boards tend to have more movement issues than narrow boards.

Conditions vary because of geographical location and the species of wood flooring being used.

If the subfloor moisture measurement comes in at 7 to 10 percent, and your hardwood measures 7 to 10 percent, it’s usually safe to assume the job site is ready for the wood, and the wood is ready for the job site.

If the job site is normalized to an in-use reading for your region, and the subfloor and the wood flooring moisture (wood flooring less than 76 mm wide) is within 4 points of each other, the flooring is acclimated and ready for installation.

The following conditions should always be established before wood flooring is delivered:

  • The building is completely enclosed (doors and windows installed).
  • Final grading has been completed, and all drainage runs away from the building.
  • All wet construction elements are completed and dry (concrete, plastering, drywall).
  • Basement and crawl space areas are dry.
  • AC and heating is functional and has been running for five days before installation.
  • Appropriate humidity and temperature inside the building have been achieved.

Once the job site is ready, and the wood flooring has been delivered, the time it will take to acclimate wood flooring will depend on:

  • Expected seasonal change for your location.
  • Manufacturer recommendations.
  • Species of the flooring to be installed.
  • Climate conditions of the job site.

It’s important to remember imported or tropical species typically require more time to acclimate because of higher density and oil and resin content.

It is recommended that you measure the moisture content of wood immediately after delivery to establish a baseline.

The most efficient way you can get an accurate wood moisture content reading is to check and measure the moisture content of 40 boards for every 1,000 square feet. Levon recommends this as well. “We check up to 40 boxes and take moisture readings on different bundles,” he says.

Another way Levon acclimates the flooring before installation is by creating an ideal environment. “The HVAC should be turned on five days before installation and left running after the job is complete. The main thing we need to accomplish is to keep the environment as close to the living environment as we can. That’s very important when it comes to a successful installation.”

An NWFA tip to keep in mind states, “Calculate what the optimal wood flooring moisture content is (baseline) by dividing the high season and the low season. Example: If your region has an expected EMC from as little as 6 percent to a high of 9 percent, the baseline moisture content of the wood is 7.5 percent.

How to Test Wood Flooring Moisture Content
Wagner Moisture Meters is the most respected moisture meter company in the world, providing flooring professionals with quality handheld devices that help establish a baseline and gather additional moisture measurements.

Moisture meters are essential to ascertain a baseline reading of wood moisture content at the time of delivery; for concrete moisture testing to ensure conditions are ready to receive wood, and for subfloor moisture testing to ensure conditions are ready to receive wood.
“My moisture meter is always with me. If I ever have a situation, it’s there. I always have it handy. If you’re a wood flooring professional, you should always have a moisture meter with you,” enthuses Levon.

How to Store Wood Flooring
Acclimation of wood flooring begins with proper storage at the job site. It should be cross stacked and spaced to encourage air circulation around the boards. Most manufacturers recommend materials acclimate for a minimum of three days with no maximum suggested.

Levon agrees. “If the flooring is unfinished, we cross stack the wood. If it’s a finished material, we read the instructions and follow the manufacturer’s recommendations. It doesn’t matter if it’s engineered or pre-finished. If there is a high content of moisture, it can still cause big problems.”

Wood Flooring Acclimation Takes as Long as It Takes
It’s important that wood floor materials reach a moisture content that is in equilibrium with expected use. To accomplish this, it will take as long as it takes. Regular moisture readings will indicate when wood flooring has stabilized, and it is in equilibrium with its environment. At that point, no further changes will occur.

Acclimating Engineered Flooring
Even with engineered flooring, it is suggested by some manufacturers that in order to retain coverage with the warranty, the job site has to be maintained between 30-50 percent relative humidity, and these conditions must also be maintained after installation.

“We don’t skip a step just because the flooring is engineered. We always check the moisture of the wood panels and the concrete. We take moisture content and relative humidity very seriously because those are two areas that can cause flooring failure,” says Levon.

Floors perform well when you invest time during the installation process to ensure moisture, temperature, and humidity are controlled and stabilized.

Failure to properly initiate wood floor acclimation before installation may compromise the integrity of the floor. Excessive gaps, warping or cupping can occur after the installation is complete; the expansion joint may also be compromised, which will result in further damage.Failure to acclimate the flooring will also void the manufacturer’s warranty if such problems arise.

When you take the time to prepare your job site location, bring the flooring in at the right time, determine the expected seasonal change for your location, and make sure everything is acclimated correctly, you’ll never have a problem with hardwood flooring.