When a Cupped Floor Has Been Rightly Installed

Ripping Out Wood Floor

There are few wood flooring problems more upsetting than cupped floors. Almost all wood floors will experience some contraction and expansion as the seasons change.

Cupping of the wood floor can be a natural reaction to these seasonal moisture changes if they occur to a minor extent. If the cupping is more severe, it could indicate a serious moisture related problem with the wood flooring.

Wood’s equilibrium moisture content (EMC) is influenced by the relative humidity (RH) and temperature of the surrounding air. Wood will lose or gain moisture until it is in balance with this surrounding environment. Higher RH usually causes the expansion of wood, because the wood absorbs the increased water moisture vapors from the air; lower RH usually causes wood to shrink as it releases the excessive water moisture vapors back into the air. Seasonal weather and RH changes can also affect and reflect changes to the wood’s EMC.

Cupped floors occur when wood curls up and the edges of the board are higher than its center. Moderate cupping can be detected from a standing position when light reflects off a cupped floor with a wavy or slightly washboard look, or it may be readily viewed by the naked eye in more extreme instances. In these cases, it can also be possibly felt underfoot.

Cupped floors can occur for the following reasons:

  1. Low indoor RH is usually the main reason if the wood flooring was installed correctly.  Sometimes, wood flooring simply absorbs enough RH from the air that the flooring expands, compression sets in as the boards are crushed together, deforming the boards at the edges. The indoor humidity of the building should be controlled in this situation
  2. A moisture imbalance can occur throughout the thickness of the wood. The wood flooring is wetter on the bottom of the board than on the top. The moisture imbalance can be proven by taking moisture meter readings on the wood flooring.
  3. Excessive water spilled on the floor from a dishwasher leak. The excessive water is absorbed into the wood causing the wood to swell, crushing the boards together, and deforming them at the edges causing cupping. The cause of the moisture leak must be identified and eliminated in order to repair the floor.
  4. A plumbing leak can allow moisture to migrate up into the subfloor and then into the wood flooring causing cupping of the floor. Again the cause of the moisture problem must be identified and eliminated in order to repair the floor. Remember that the minor cupping can be due to the seasonal effects of MC changes in the wood floor and not necessarily on poor installation. It is also important to know that seasonal effects will always be present because seasons bring RH changes to our environment. Some cupping occurs naturally, but excessive cupping curls floors in a way that can require remediation.

Avoiding cupping begins before the wood flooring installation, of course. First, by measuring the RH of a concrete subfloor or by measuring the MC of the plywood or OSB wood subfloor with appropriate moisture measurement equipment, you can eliminate the subfloor MC as the cupping’s culprit.

Contractors and consumers can preempt cupping by measuring and monitoring the MC in the subflooring materials and in the wood flooring previous to installation. A wood floor is good to go when it reaches it’s EMC. Accurate moisture measurement in all of the pre-installation stages will ensure that the wood flooring will give the best performance homeowners expect.

If the cupping occurs after a proper flooring installation, moisture measurement still provides a key to solving the problem. A moisture inspection can identify problems that may have occurred after installation – like a leaking pipe – and give clues to the best solution possible. Once the source of the moisture problem is controlled, cupping can usually be cured.  That’s great for wood floors, and the people who love them.

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Ron Smith

Ron is an application specialist for Wagner Meters, and has over 30 years of experience in instrumentation and measurement systems in different industries. In previous positions, he has served as a regional sales manager, product and projects manager, and sales manager with manufacturers involved in measurement instrumentation.

12 Comments

  1. Cmaey says:

    Thanks for the info. I had a flood in my kitchen in Aug. 2013. My flooding is hard wood. the contractor let the floor dry out for 3 months now it is cupping and I am trying to find out what I need to do about it.

    • SP says:

      Cmaey, could you please tell me what the contractor did to fix this issue? Is your subfloor ok? We had a minor flood last weelk in our kitchen and we are drying the floor with utility fans now.

  2. Rick says:

    having issues with new Brazilian Pecan solid wood floors. Do you know experts in the Garland/Dallas area who can identify the issues with cupping?

  3. John Needham says:

    Had solid strand woven bamboo laid in all living areas (not bathrooms or utility) as part of a total renovation about 2 months ago and have underfloor heating. Within a couple of weeks, the planks began to ‘cup’ in most rooms, some areas worse than others. Bought flooring from Bamboo flooring company who said the cupping was within acceptable limits but we can feel it underfoot when walking round without footwear. Installers have said not their responsibility as the product must be inferior. Have to wait and see what happens now and will have to employ an independent door assessor to find out where the fault lays …. anyone else had this problem and did it resolve itself?

    • KG says:

      Yes, we just moved into a new house and replaced laminate floors with solid strand woven bamboo floors at the beginning of April. We did have one small spill near the laundry room that we cleaned up immediately. We installed mostly all downstairs (except the master bedroom/bath). Everywhere installed is cupped, and like you mentioned some areas worse than others. We bought ours from Lumber Liquidators and they used a contracting company to install. The guy that came back out walked in and noticed it immediately, but wasn’t able to do much. He mentioned that a second team would have to come out with different tools to identify the main issue.

      He did mention that before they do any job, the crawl space underneath the house must be fully covered with plastic to avoid moisture. Ours is not fully covered up to the wall and some dirt show in other areas and he thinks that moisture may be the problem. He also said that they are not supposed to start a job if that is not done, so hopefully they can get this resolved if that is the issue. If the issue is found, the installer mentioned that the floors could potentially go back into shape but we are only on the beginning stages so we will see.

  4. Terry says:

    please help me on a subject my floors are hardwoods and they are starting to have raves under the foot is it because i have a crawl space? this didnt happen before….

  5. Marty Lumley says:

    About a year ago, we added new hardwood flooring in our family room and dining rooms. The family room floor connects to kitchen hardwood and was feathered in. Noe both new hardwood is cupping, visually and can be felt as we walk on. Original kitchen flooring if fine. What is the cause and then what can be done?

    • Jason Spangler says:

      Marty:

      Thanks for the question. It may be an acclimation problem prior to installation, but the best way to figure it out for sure is to contact the National Hardwood Flooring Association at NWFA.org and look for a certified wood flooring inspector that can come out and physically look at the problem and properly diagnose the issue(s). I hope this helps.

      Thanks,

      Jason

  6. Hi Ron,
    We recently installed Red Birch throughout the whole house. The install was done in August 2017, we live in the northeast (Upstate New York). I noticed, a couple weeks after install, that some of the boards have cracking down the middle of them. After further investigation I noticed that there are several large and small cracks in the hard wood. I was concerned so I called the company where I bought them. The lumber store came to my house and so did a rep from the flooring manufacture. Before they even looked at the cracks they placed a moisture reader on the floors. It 9 – 12%. They then told me it was basically my fault because the moisture reading was mildly elevated. We then checked the basement and the humidity in the basement is normal and we all agreed that my home is “dry”. I feel that there is an issue with the flooring I bought. The rep also noticed some cupping. We also all agreed that the installation was done properly and that we acclimated all the wood at least 5 – 10 days before install in our house. My question is what is a normal moisture reading for hard wood floors newly installed in my home. And, my concern is that every house in my neighborhood has hard wood and I believe that if the floors were checked in these homes than the readings wood be the same.
    Any advice wood be great:)
    Thank You
    Jess E.

    • Jason Spangler says:

      Jess:

      Thanks for the comment. “Normal” moisture readings can vary. Most manufacturers will state that they manufacturer their floors to a 6-8%MC level. Obviously, after the manufacturer, it depends on what kind of ambient environmental conditions the floor is subject to in determining what the MC% is prior to being delivered to your home. Once in the home, it then needs to acclimate, as you stated, to that environment. All of this being said, “normal” is whatever level RH% and temperature a homeowner keeps their house because, ultimately, this is the MC% level the wood is going to emulate. Here are a couple of informational links that may help more: http://www.woodfloorsonline.com/techtalk/US_moisture_map.html. We also have a free smart device app that will calculate equilibrium moisture content, say for your specific home, given you can measure the RH% and temperature in the environment: https://www.wagnermeters.com/wood-moisture-mobile/.

      Hope this helps.

      Jason

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