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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Last updated on May 4th, 2021

35 Comments

  1. Christy says:

    Hi, I recently (2 months ago) had 3/4 wood floors installed.. My floors are cupped a little in places and some of the top coat is coming off also. The store I bought it from sent a 3rd party person that completely got different moisture readings than the person that checked the moisture levels for me.. I feel like they are giving me misleading information because they want to was their hands of me and my floor.. The guy they sent also took a moisture reading inside my air conditioning floor vent.. I feel that was misleading because of condensation.. Please give me some advice..

    • Jason Wright says:

      Christy,

      Please give me a call at 1.800.634.9961 ext.212 so we can talk in more depth about this.

      Thanks.

  2. Gavin Lyman says:

    It’s great to read a post of yours, the information you gave us is not found anywhere. You keep giving us more information like this, we follow you.

  3. Doris Ann Rutledge says:

    We’ve lived in our house for 16 years, have 3/4 inch hickory floors which have cupped. This happened not long after they were installed. My husband seems to think this happened as a result of the boards being right against the wall board with no wiggle room on either end of the living room. Is this possible the floor was layed incorrectly with no room for expansion? We don’t have and have never had moisture problems in our house.
    Thanks for your thoughts!

    • Jason Spangler says:

      Doris:

      Thanks for the question. While expansion is important to accommodate changes in wood floors throughout the year, the cupping is going to be related to a moisture imbalance. This could be a situation where the wood wasn’t acclimated enough prior to installation, moisture is coming up from below, or possibly the environmental conditions in the house have dried out causing the issue. I would recommend you have a certified wood flooring inspector come out and evaluate the situation. You can find one here https://www.woodfloors.org/certified-inspector.aspx Good luck.

  4. John O'Mara says:

    I recently had an oak hardwood floor installed in my kitchen. The width of the oak wood is 3 1/4 inch. I have old oak floors in all of the rooms in my house. Never had any problems with the floors cupping. The kitchen floor was installed 2 two months ago. I’m starting to notice minor cupping on this kitchen floor. The person who installed the floor did not use and underlayment material. The hardwood oak flooring was fastened to new 1/4 inch plywood sheets which were nailed to the subfloor. Below my kitchen is a finished basement. The laundry tub is directly above the kitchen. There is a higher level of moisture in the kitchen. The flooring was sitting in my living room which is next to the kitchen for six weeks before it was installed. Any ideas why my kitchen floors are starting to cup. Thank you for reading my letter.

    • Jason Spangler says:

      John:

      Thanks for the question. There could be multiple things going on here like the moisture differential between the basement and the kitchen space or maybe the flooring didn’t fully acclimate. Instead of guessing though, I would seek out a certified wood flooring inspector and have them evaluate the situation. You can find one at https://www.woodfloors.org/certified-inspector.aspx Good luck.

  5. Tom Petroliunas says:

    Jason,
    My house is a raised ranch which had 2 1/4″ white oak through most of the upper level. In April 2019 we remodeled and hired a flooring company to finish putting in the same type of oak floor in the remaining areas of the upper level. One room required finger jointing/weaving the old floor with the new floor . The subfloor is t & g plywood. The old floors have a 15 lb. felt underlayment/moisture barrier and I’m not sure what the contractor used as underlayment for the new floor. I just know that it wasn’t roofing felt. They let the new floors acclimate for a week before installing but I don’t know if they took moisture readings. Around the Fourth of July we noticed cupping on the new floor only and it wasn’t localized but occurred throughout the new floor area. The old floor is not cupped, even right next to the new floor in the finger joint area. Never any issue with the old floors other than a little squeaking and a few , moderately large joints.
    I don’t know what to do or how this condition exists. Should the contractor have used roofing felt? If he had measured the moisture in the new flooring and the subfloor and the readings were nominal, could my new floor cup but not the old floor? Or, Is it more likely that he didn’t measure and moisture levels were off?
    Thanks

    • Jason Spangler says:

      Tom:

      Thanks for the question. Without having the information about moisture testing or the specifics on the underlayment it makes it hard to know what the issue is. It could be an acclimation issue, vapor retarder issue, and/or a localized ambient air space issue. I would recommend that you contact a certified wood flooring inspector to look at the project, collect all of the relevant information, and then present you with the facts. Anything less than that would be speculation, especially with the various possibilities. Look at http://www.nwfa.org for a certified inspector. Please let me know if you have any other questions.

      Jason

  6. Tom says:

    Hello Steve
    We have been in our house for about 17 months (new build). The floors were copied the day we moved in to the house. My builder said it is normal and by spring it should settle. Spring and summer have gone and the floors are still cupped. I ran two dehumidifiers in the basement for six months, through winter and spring at the recommendation of my builder. They are still cupped. The floor installer has suggested that he is confident that the moisture levels are settled now (he is going to measure that) and that sanding then will be fine because the moisture is gone. He claims he has all the documents that state the appropriate moisture levels to the wood and house prior to installation, but I’m not sure how valid that is.
    Bottom line…. If the readings of moisture level are fine, is sanding the floor a good option?

    • Jason Spangler says:

      Tom:

      The answer to your question is: it may be. I would recommend that you contact http://www.nwfa.org and find a certified wood flooring inspector in your area to evaluate the floor and with that information, determine the best course of action. Good luck!

      Jason

  7. Steve Budra says:

    Hi Jason,

    Thanks for your prompt response. I thought about removing the batt insulation beneath the now insulated duct but since my basement is unheated – other than heat emanating from the gas furnace which is about 10′ away – I’ve been hesitant to do it. I agree that it’s definitely related to the duct since all other ducts in the basement run perpendicular to the joists and are hung below them with batt insulation between the joists; the wood floors above are perfect.

    I may try to squeeze 12″ wide thin insulation wrap above the insulated duct and attach it to the subfloor. It won’t be perfect since there’s 14-1/2″ between the joists but it may provide enough of a barrier between the duct and allow some air flow around it. What do you think?

    Thanks,

    Steve

    • Jason Spangler says:

      Steve:

      I think it’s worth a try. If you are using a vinyl backed wrap you might want to get some seam tape to cut up a couple of pieces and get the entire 14 1/2” coverage to avoid any question.

  8. Steve Budra says:

    Jason, I installed 4-1/4″ red oak plank (sanded and poly’d) in my kitchen about three years ago over a paper moisture barrier replacing a vinyl floor. Last fall I noticed some cupping in a narrow swath just above a 6″ heating/cooling duct that runs between two floor joists. It’s most noticeable when coming up my basement stairs as the slider to our deck is across from the basement door and the sunlight shows the irregularities. Originally, the duct itself wasn’t insulated and roll insulation was simply hung beneath it between the joists. The duct is close to the subfloor and isn’t really movable so I can’t reposition the insulation above it but I was able to slide a seamless foil/sleeve over the duct and taped the ends with foil tape. I rehung the insulation beneath the duct. I suspect moisture from the central AC system during the summer months must be condensing on the subfloor bottom and migrating up to the hardwood but I thought the insulation sleeve would have solved it. I’ll continue to monitor it and imagine during the heating season that drier air will cause the wood to shrink, but I also installed a whole house humidifier last year to provide moisture during the heating season.

    What would you suggest? Thanks for any insight you can provide.

    Steve in MA

    • Jason Spangler says:

      Steve:

      Thanks for the questions. I guess first, your idea of monitoring, especially with the various changes you have made, is a good initial course of action. The only thought I have is with the insulation encasing the duct in a confined space. I think the wrap is good, just not sure about the insulation beneath it. I am wondering if by encasing it, you may be making it worse. I might try to find a way to insulate the joist space, but leave the duct exposed so it doesn’t have as much potential to impact the entire joist space. Good luck.

      Jason

  9. Sam Thompson says:

    we just had a new floor installed 3 months ago, I am noticing some cupping in a 4ft area only, and by the back door only. we have not had any leaks, spills or water at all on the floor. we only clean with Swiffer mops. No water mops. The installer is not getting back to us says he is trying to find a reason and to repair it. I am open for ideas. it was also a new subflooring. Thank you

    • Jason Spangler says:

      Sam:

      Thanks for the question. It’s hard to say why this happened exactly, but in order for a floor to cup, there has to be a moisture differential from the top to the bottom of the floor plank. That being said, if there are no water leaks that have caused this, then we have to start looking at ambient air conditions (is the door opening not sealing properly, allowing drastic ambient conditions from outside to affect the surface), is there a crawlspace issue in that area specifically, etc. You can find a certified flooring inspector if you would like to have the potential cause diagnosed. You can find one in your area at http://www.nfwa.org. Good luck.

      Thanks,

      Jason

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