How Long Does It Take to Acclimate Hardwood Flooring?

Wood Flooring

Written by Wagner Meters, published first by ProInstaller (Spring 2015)

There is a common misconception among contractors that if you bring wood flooring into the workplace and let it sit for a few days, it will acclimate properly and be ready to install. This is a big mistake that costs flooring contractors time and money.

According to the National Wood Flooring Association (NWFA), wood floor acclimation is “the process of adjusting (conditioning) the moisture content of wood flooring to the environment in which it is expected to perform”.

Contrary to belief, it has less do with the amount of time you should let flooring sit to acclimate on the job site and more to do with monitoring the moisture content of various components.

It is a fact that wood flooring will always perform best when the environment is controlled and remains within a relative humidity range of 30-50%. The temperature should also be controlled within a range of 60-80 degrees Fahrenheit.

Job Site Preparation before Wood Flooring Acclimation

Wood flooring installation should always be the last job of any construction project.

Certain conditions should be met before wood flooring is delivered to the job site.

Make sure the job site is ready for the wood, and the wood is ready for the job site. Wet elements including plaster and paint should be completed and dry before the wood is delivered to the job site.

We asked Levon Karapetyan from Northern California’s prestigious Artex Flooring Inc. how he prepared a job site for delivery of wood flooring…he said, “Before we receive a shipment of wood flooring, we monitor the job site to make sure the relative humidity is in compliance with recommended standards, which is 35-60%. 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 with useful information.

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

We asked Levon how he deals with builders or clients insisting flooring gets installed when conditions aren’t suitable, and he said, “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.”

Wood FloorWhen asked if he runs into humidity problems with new construction settings he explained, “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.”

As Levon mentioned, it’s always better to delay bringing in wood flooring materials if the walls were just painted or the subfloor isn’t completely dry. 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. This definition is defined by the NWFA along with other useful resources.

If acclimated wood flooring is delivered to a job site while the contractors are still painting, the wood flooring will absorb the moisture of the paint, increasing the moisture content of the wood.

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% moisture content difference between the flooring and the subfloor. For wider flooring (more than 76 mm wide) there should never be more than a 2% moisture content difference. Wider boards tend to have more movement issues than narrow boards.

Conditions of our example below may vary because of your geographical location and the species of wood flooring you are using:

If the subfloor moisture measurement comes in at 7-10% (measuring with a properly calibrated wood moisture meter) and your hardwood measures in at 7-10%, 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 or heating is functional and has been running for five days prior to installation
  • Appropriate humidity and temperature inside 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

Imported species or tropical species typically require more time to acclimate because of higher density and oil and resin content.

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

The most efficient way you can record accurate wood moisture content and representation is to check and measure the moisture content of 40 boards for every 1,000 square feet.

Levon agreed with this statement saying, “We check up to 40 boxes and take moisture readings on different bundles.”

When we asked Levon if there was anything else he did to help acclimate product prior to installation he said, “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.”

Useful Tip:
As the NWFA suggests, “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 a low of 6% to a high of 9%, the baseline moisture content of the wood would be 7.5%.

How to Test Wood Flooring Moisture Content:
Wagner 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 you can record and keep an eye on.

These devices are instrumental in establishing:
-A baseline reading of wood moisture content at time of delivery
-Concrete moisture testing to ensure conditions are ready to receive wood
-Subfloor moisture testing to ensure conditions are ready to receive wood
-Changes in wood flooring as it acclimates to room

Wagner Meters carries various wood moisture and concrete moisture meters that take the guesswork out of the acclimation process by providing accurate moisture readings you can depend on.

Wagner Meters MMC220 Moisture MeterThese meters are the most valuable instruments used in the acclimation process. They measure the moisture content of the subfloor, concrete and the moisture content of the wood flooring to be installed. These measurements will provide you with precise and accurate conditions that will help eliminate flooring failure if conditions are not suitable.

Moisture measurements will also help you decide if the subfloor or concrete at the job site are dry enough to receive wood flooring. If the subfloor is too wet, moisture will be absorbed into wood flooring materials and flooring will expand and buckle.

If flooring materials retain moisture at the time of installation, the flooring will shrink when equilibrium (EMC) has been reached, which will cause wide gaps and spaces in the flooring.

These moisture content measurements are crucial if you have a problem with faulty flooring received from the manufacturer. The warranty of many manufacturers will be void if you can’t back up your work with solid evidence.

Levon highly recommends moisture meters to flooring professionals: “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.”

How to Store Wood Flooring:
Acclimation of wood flooring begins with proper storage at the job site.

Wood floor acclimation can be achieved by cross-stacking and spacing wood floor materials to encourage air circulation around the boards. Most manufacturers recommend materials acclimate for a minimum of three days with no maximum suggested.

In order to make a proper judgment call on how much time is needed to acclimate your wood flooring, you need to have a baseline and know what the moisture content of wood flooring is when it is delivered.

Levon shared his on-site storage methods with us: “If the flooring is an unfinished material, 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. In order 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 (EMC) with its environment. At that point, no further changes will occur.

Wood Floor Acclimation with 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% relative humidity, and these conditions must also be maintained after installation.

When asked if Levon acclimates engineered flooring, he said, “We don’t skip a step just because the flooring is engineered flooring. 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.”

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 begins may compromise the integrity of your 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 it 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.

Click here to decide which moisture meter is right for you.

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Larry Loffer

Larry Loffer is a senior technician at Wagner Meters, where he has over 30 years of experience in wood moisture measurement. With a degree in Computer Systems, Larry is involved in both hardware and software development of wood moisture measurement solutions.

7 Comments

  1. Me the floor guy says:

    I’m beginning to believe that hardwood manufactors are drying the wood too much. I’m 3rd generation hardwood pro, been doing it everyday for over 20 years and I’m in the south so this may not be an issue in other parts of the country. We live and work in the south, our wood comes from the south. Here’s my theory. It seems that almost every hardwood delivery is under 3% moisture. In wide wood over 3 and 1/4 you will see cupping at 7% and under. Doing new construction you never really know where the house will settle after a complet season, if it’s an addition with hardwood existing it’s a lot easier to determine where you think it will settle. Its never guaranteed as new construction is a lot better than say 40 years ago, so a lot of time the new will hold less. Ok back to my theory manufactors are producing wood under 3% so if you deliver to a normal new construction site just the aculmation process is going to cause the boards to start cupping even before the instlation process begains. Say the house is going to hold around 8% (which is great if you live in GA) the 5% gain will defiently affect the floor. And if the wet Rainey, humid season hits just after the instlation or sanding process it can jump 3 to 4 points, I’ve personally seen 2 to 3% cause major headaches in floors over 4 inches in width No matter if it’s no more that a 3% difference between sub and your flooring when installed. I personally think the NWFA should hold manufacters in different parts of the country to different standrads, say in the south I don’t believe floors should be dried under at minum 5% Pretty much every house in the southeast is gonna hold around 7% or more, very few ocations will it hold less. So if it’s under 3 and climbs to 7 or say 9 your headed for a problem, your either going to fight it together( after its slightly cupped and the tongue and grove has actually swollen ) or put it in early and let it aclmate installed nailed to the floor which has its own problem areas( cupping and popping) so if it was dried down to around 5%, 2 to 3 % would be a lot less affected and could reasonably be aclimated in around a week. But natural products have a mind of there own sometimes. Curently sanding new 4 inch (builder installed his self) floor reads 7% but is cupped like crazy which is bad for people buying house sure to have issues with popping down the road. Sorry to ramble on but I’ll sum it up right here. I think the NWFA should set different standards for different regions in the south wood should probably not be dried under 5%, say out west in your dryer regions under 3 may be acceptable. But not in the south.

  2. I love the look of oak floors, and I plan on having it installed in the spring. I want it to be perfect, so it is important that the wood has time to acclimate. It’s very dry where I live, so I doubt the humidity would level would fall in the 30-60% range. Should I humidify my house before I order the timber?

    • Larry Loffer says:

      Hi Kairi,

      It is important to allow the flooring to equilibrate in the environment it will be installed. It’s even more important to maintain a constant level of humidity as much as possible.

      A moisture meter such as our Wagner MMC220 can measure every piece of flooring before installation to confirm even moisture content. Our TH-200 Thermo-Hygrometer monitors temperature and humidity. These two tools along with our free WoodH2O app are essential for a successful flooring installation.

      Please visit http://www.wagnermeters.com/wood-flooring/ for more info and free flooring articles.

      • Bob Pasi says:

        Larry, nice article with good information concerning MC, temp, and RH and other factors to consider before installing wood flooring. However, I do have a question as to which installation method is best to use after the MC, RH, and temp are at ideal conditions.

        My wife and I live in Houston, TX and live in a single story house built over a concrete slab. The house is 22 years old. Our indoor RH is ~50%-55%. We would like to replace the existing vinyl and carpet flooring throughout the house and was looking at engineering wood flooring or tiled flooring that looks like wood.

        We called various contractors and all seemed to offer up their own suggestion as to the type of installation regarding the wood flooring. Some say we should use a floating floor system, others want to build up the existing flooring ~ 1 1/2″ with wood underlayment and then nail in place, while others say go with glue.

        Assuming that the concrete slab is completely dry and can accept wood flooring which of the three methods (floating, nail in place, or glue down) would be best to use here in Houston, TX. Thanks for your time.

        • Larry Loffer says:

          Bob,

          Since this is more of an application question rather than moisture related, I will refer you to the National Wood Flooring Association (NWFA.org). They can answer this question.

  3. Audrey says:

    I think it’s unfortunate that most sellers of wood flooring do not make the customer fully aware of the preparation issues. We bought a very nice engineered floor, yet we are now into a full week and still not able to install. If we had known this we would have ordered it and had it delivered much sooner, thought we just needed to get it there and the installer would come and put it in. The contractor says he will not install until it’s ready and although it is a major inconvenience now, we will regret it soon after. I am looking forward to the new floor, just frustrated and worried that we may have purchased a defective product since it has been almost a week and acclimation is not complete. Do you know how long we would have to wait before we actually learned that the flooring is not going to get any better? Feeling frustrated.
    Thank you for all of the interesting information, wish I had seen this sooner!

    • Larry Loffer says:

      Your installer is doing the right thing. It is very important to let the flooring acclimate in its installation environment before installation. This allows the flooring to slightly expand/shrink as it adjusts to its new environment BEFORE it is installed.

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