Wood Floor Cupping and Crowning: Spotting Trouble

Man Repairing Wood Flooring

Installing wood floors is a big decision. Wood lovers eagerly anticipate successful installation and they watch for problems. However, many homeowners and installers do not recognize that the wood moisture content (MC) of the wood flooring optimally must be measured and monitored before, during and after installation for the lifetime of the wood floor.

Seasonal Problems

Sun and RainThe key is to know potential wood flooring MC problems before they arise. After installing wood floors, it is necessary to recognize that wood always loses or gains moisture depending upon the relative humidity (RH) and temperature of the surrounding environment. Specifically, wood shrinks as it loses MC. When the cold of winter causes people to turn up the heat in their homes, the RH levels in the home plummet and the wood flooring boards can shrink, and spaces appear between the boards. Wood expands when it absorbs MC from the more humid air, such as when people turn off the heat in spring and moisture returns to the air. Ironic isn’t it? Seasonal transitions bring two potential seasons of weather to the spaces between wood flooring boards.

Now for the tricky part. Expansion and contraction of the wood flooring are as normal as the RH seasonal changes are. Therefore, owners can expect some gaps to form between their wood flooring in winter months; those gaps may naturally close in spring.

Achy Joints

In order to treat those achy wood joints, wood flooring owners should invest in a wood moisture meter. It is a tool designed to measure the MC levels in wood flooring usually up to 3/4” deep into the wood. Lumber producers and contractors use wood moisture meter products as trade tools when installing wood floors. Optimally, wood must reach its equilibrium moisture content (EMC), a point of balance between the MC of the wood and the RH of its ambient environment. Mills process lumber to try to reach its EMC target, but installers still need to confirm that the MC of the wood is stable for installation purposes after the manufacturing process.

Wood flooring owners should also monitor the MC of the wood flooring after installation to remediate any potential future moisture related problems.

Cupping, Crowning, and Buckling

Cupping Illustration

Cupping occurs when the edges of a board are higher than its center. Assuming the flooring has been properly installed, cupping can occur due to excessive moisture which causes the wood flooring to swell, crushing the boards together and deforming them at the edges. The board edges form a “cup” due to excessive MC in the flooring. The first step to remediation is to identify the moisture source: high indoor RH, a water spill, a leak from a dishwasher hose or a plumbing leak, for example. Once the cause of the moisture is identified and controlled, cupping can possibly be reversed. Wood flooring owners can use a wood moisture meter to identify MC changes on a regular basis before cupping occurs.

Crowning Illustration

Crowning is the opposite; the center of a board is higher than its edges. This can occur when the surface of the floor encounters moisture or is left in wet or humid conditions for an extended period of time. Crowning may also occur due to previous floor cupping problems. If the floor is cupped, the floor should be given ample time to dry. If the floor is sanded while the boards remain cupped and moisture is still present, the sanding process can sand off the top edges of the board and thus, the edges are lower than the rest of the board when it returns to a normal MC.

Buckling occurs when wood flooring actually pulls away from its sub-floor, lifting up to several inches  in one or more places. This is one of the most extreme reactions to moisture that can occur in wood flooring applications. Fortunately, this does not happen often. The most common reason that buckling occurs is after a floor has been flooded for a period of time. Other causes on nailed floors might be insufficient nailing, incorrect nails or incorrect subfloor construction. On glued floors, use of incorrect or insufficient mastics to an inadequate mastic transfer, a subfloor separation or a subfloor contamination can cause buckling.

Any MC imbalance creates possible problems in all wood. With a wood moisture meter, flooring owners may find MC problems in time to pre-empt flooring problems or failures.

Moisture Meter

The wood moisture meter has come a long way. Wagner Meters, a company formed in 1965, carries wood moisture meter products for lumber mills, building inspectors, installation contractors, wood hobbyists and wood flooring owners. Obviously, these are primary tools for the expert flooring installer and building inspector, but homeowners can benefit from their quick “scan” capabilities as part of their regular home maintenance. Wagner Meters pinless technology allows the user to accurately scan the wood without the time-consuming effort of driving pins into the wood and damaging the wood’s surface.

The Wagner Meters MMC220 Extended Range wood moisture meter measures the MC in wood flooring and woodworking applications. The MMC220 measures the MC between 5-30%. This Wagner Meters hand-held device also assesses hardwoods, softwoods, and tropical wood species.

For more general building materials, Wagner Meters BI2200 Building Inspection moisture meter measures wood, sheetrock, concrete and many more building materials for non-damaging moisture checks throughout the home.

Spotting MC problems in advance in building structures and in wood flooring and other wood products in your home or business is a preemptive act of successfully maintaining the value of your investments.

Jason has 20+ years’ experience in sales and sales management in a spectrum of industries and has successfully launched a variety of products to the market, including the original Rapid RH® concrete moisture tests. He currently works with Wagner Meters as our Rapid RH® product sales manager.

30 Comments

  1. bert says:

    If I set up tent over damp hard wood floors and put a humidifier hooked to it will it in reversing cupping its in a small area ?

  2. Kathryn A says:

    water spilled on my wooden floor and i have minor cupping as a result. can this be reversed? it is tongue and groove bamboo flooring.

    • Jason Spangler says:

      Kathryn,

      Thanks for the comment. The answer is maybe, but I would guess it will never be complete as it was originally. No more water issues being experienced, the best chances are to have ambient conditions that are consistent and dry enough to allow the moisture to move out of the floor. My guess is that it will take an extended period of time (months) for you to see the end result.

      Regards,

      Jason

  3. MR TOM CORBETT says:

    I have had a leak in the bathroom toliet, valve went drips spread into carpet and under floor boards. There is cupping about 1/8 of boards slight. O have solved the problem, I work away, can the boards dry out in ambient conditions in the flatnaturally over months

    • Jason Spangler says:

      Mr. Corbett:

      Thanks for the comments. With a cupped floor like this, they may not ever go back to their “original” state, but they will probably lessen in their degree of cupping. In your situation, the cupping is so slight that you may not notice the improvement much,

      Thanks.

  4. Eric says:

    We have just bought a home, and after taking a hot shower, our wood floor in the kitchen is crowning in one area. Can the boards go back to normal if we find the source of the moisture and let it dry? Or does it have to be replaced ?

    • Jason Spangler says:

      Eric:

      Thanks for the comment. It depends on the extent of the damage. Unless it’s a hazard, the best course of short-term action is probably watch and wait. Good luck.

      Thank you,

      Jason

  5. Valerie Ewing says:

    Eric, we had all new hardwood installed in our renavated home. We are their 4 months, I noticed the cupping right away, my builder said that the wood was tested for moisture and passed. He said it was due to a rainy several days after install. He said there is nothing we can do about it. We are sick over it as it is very noticeable. Is there anything we can do to fix this, will it get better or worse overtime. We spent a lot of money on this renovation and are so upset, the house has an open floor plan and therefore it’s throughout all of the open living area. Any information you have regarding this problem and how to fix it would really help.

    Thank you
    Valerie Ewing

    • Jason Spangler says:

      Valerie:

      It may “relax”, over time, depending on what really caused the issue. I would visit http://www.woodfloors.org and find a certified inspector to come out and do a thorough report on the issues, remedies, and causes so you can try to completely understand. Knowledge is power in this type of situation.

      Good luck.

      Jason Spangler

  6. Sue Cobb says:

    Hi Jason,
    We are considering hardwood (ash) flooring for a mountain home where there is very low humidity, especially in the winter. We are not there all of the time and are wondering if you know of any whole house humidifiers that could be programmed remotely to keep the humidity at a decent, consistent level while we’re away. We have baseboard heaters.
    Thank you.

  7. Elena says:

    We just moved to 6 year old home and after few days of heavy rain most of our living room floor boards are cupping. We believe the water could get underneath from the gutter. Is there any simpler solution to improve situation rather than replacing the floor as suggested by technician? This may happen again and we are puzzled.

    • Jason Spangler says:

      Elena:

      Thanks for the questions. First, I wouldn’t fix any symptom (the cupping) until I knew for sure I had fixed the problem. Unless, obviously, there is some eminent danger of bodily harm due to the cupping. If the gutters are thought to be the culprit find out why and remedy it. Then, once you have that fixed and the floors aren’t getting continuously wet, you can see if any of the damage slowly goes away. Keep in mind, wood can absorb and expel moisture, depending on the severity of the damage and length of time. With that, some of the cupping may “fix” itself as the floor starts release the moisture. Good luck.

    • Michelle Krein says:

      Elena:

      Thanks for the questions. First, I wouldn’t fix any symptom (the cupping) until I knew for sure I had fixed the problem. Unless, obviously, there is some imminent danger of bodily harm due to the cupping. If the gutters are thought to be the culprit find out why and remedy it. Then, once you have that fixed and the floors aren’t getting continuously wet, you can see if any of the damage slowly goes away. Keep in mind, wood can absorb and expel moisture, depending on the severity of the damage and length of time. With that, some of the cupping may “fix” itself as the floor starts release the moisture. Good luck.

  8. Nathalie A says:

    Hello, Jason. I’m hoping you can provide advice. I had 3 1/4″ maple hardwood (Lauzon) installed on my second floor last May (2017). I live in southeastern PA, where it is dry in the winter and humid in the summer. I run my A/C at 73 degrees all summer. Within about a month of installation, the floor cupped, just about every plank throughout the entire floor. The installers told me to wait to see if they uncupped during the winter, which they did. Now that its summer again, they’re badly cupped again. It is uncomfortable to walk in bare feet.

    The current RH in my house is about 42%. The installer showed a floor humidity level of 8%. That seems reasonable to me, right?

    After much recent research, not knowing anything about hardwood floors prior to installation, I realize that they only allowed the flooring to acclimate in the boxes for 1/2 day. The owner says that it doesn’t matter because they were kept in a temperature-controlled warehouse. I don’t see how that applies to the RH, etc, in my own home. He says if they replace my flooring, the cupping is likely to happen again. I am at a standstill, not knowing what to do. I do see that a wooden drawer in a piece of furniture has swelled since the winter and now won’t close. Perhaps humidity is a big factor in my house? Yet the humidity level seems to be within normal limits, and every other home I’ve been to in the area does not have cupping, and I know they don’t have dehumidifiers.

    Do I take the safe route and replace with carpet or engineered flooring? I wish I knew definitively if the cupping is a result of improper installation, or just the way the humidity is happening in my house.

    Thanks for your help.

    • Jason Spangler says:

      Nathalie:

      Thanks for the question. I can’t answer the question of installation proficiency, but I can make a few general observations. For the floor to cup and then “relax”, there has to be changes in the moisture conditions within the house. Now, I don’t know if it is a change in conditions (RH% and temp) on just the bottom floor which is impacting the upper floor, just the second floor, or possibly uniform, seasonal changes throughout the entire house. You question other people not having dehumidifiers and having no issues. Keep in mind, many humidification/dehumidification solutions are integrated into the HVAC systems within houses. Some would probably not even know they were integrated into the system. In certain instances, different homes may also have drastically different efficiencies based on construction practices. Personally, I would need more information before I made a switch in flooring finish and you should be aware that you can still have this same issue even with engineered products. I would want to have evidence, either way, what the RH% and air temp do throughout the year. Knowing this may allow you to just look at improvements that can be done to allow for a consistent environment for you and the floor. Here is a product that will log those conditions over time and allow you to quantify the variations if there are any https://www.wagnermeters.com/shop/smart-logger/. Good luck.

  9. Marc Vickers says:

    I had a slow leak from under my kitchen sink and I have hardwood floors covered with linoleum. I have severe cupping in the floor. Will I need to remove linoleum for it to be able to dry out? Suggestions.

    Marc

    • Jason Spangler says:

      Marc:

      Thanks for the question. As far as removing the linoleum, it will be much easier to dry out the subfloor and/or determine the extent of the damage without the linoleum. Good luck.

  10. Tamieke says:

    In our renovation we we polished up some old hardwood flooring but had to pull up some sections damaged boards and replace them. It all looked really great and matched up well. We have since sanded and varnished the total area. After a few weeks we noticed the new boards have cuped. Shall we re-sand the cuped area or is it possible that they will then crown?
    Thanks

    • Jason Spangler says:

      Tamieke:

      Thanks for the question. First, I would want to know why the boards cupped and do what I could to remedy the situation. The boards may “relax” if the situation is remedied and the cupping isn’t too severe. Sanding the boards, when cupped, thins out the edges and could create varying problems in the future. Good luck.

      Thanks,

  11. Eugene Morvant says:

    I live in south Louisiana — our house is 70 years old elevated on cement blocks. The original flooring is oak which we recently covered with covered with vinyl planks. We also insulated the underneath of our house. Since then we have noticed cupping of the original wood flooring. Before we rip up the vinyl planks is it possible that the cupping might flatten during the winter?

    • Jason Spangler says:

      Eugene:

      Thanks for the questions. The answer is maybe. If I had to guess though, by insulating the underneath and installing the plank on top, you have altered the woods “normal” environment from the last 70 years and created an assembly where the moisture may have a harder time equilibrating and the wood may not “relax” completely. Good luck.

  12. Stephanie says:

    Hi Jason, My father and I returned to our house from our cottage to find the kitchen flooded, and below that the furnace room too. Outside of the kitchen is our dining room with hardwood flooring. 2 pieces have swelled to the point where the gap between has elevated the edges to almost 45 degrees. We had a pipe burst in the ceiling of the basement and that sprayed water up into the subfloor. As we were away, I’m not sure how long the hardwood was flooded. I’m assuming the only option at this point is replacing??

    • Jason Spangler says:

      Stephanie:

      Thanks for the question and sorry to hear about the troubles. At the minimum, it sounds like the two pieces you have described may need to be replaced. Upon removal of those, there may be more visible sections that need to be replaced proactively. Getting a qualified wood flooring installer or inspector may help to identify the extent of replacement necessary. Good luck.

      Jason

  13. Daphne says:

    Hello: I had my waxed red oak floors sanded, stained and refinished. There is cupping that has occurred in the middle of my floor where there is no
    water leak issue that I can find. It’s strange because some of the parquets are cupped while one next to the cupped one
    is OK… I am wondering if somehow the floor guys spilled stain which seeped down through the cracks separating the parquets
    and has now caused the cupping… Since I can’t determine a source for a water leak… I live in an apartment, should I place
    fans or a fan w/ a heater element to blow over the cupped parquet squares. In an attempt to dry out and reverse the cupping?

    • Jason Spangler says:

      Daphne:

      Thanks for the questions. Your idea of airflow may be a good idea and, if there isn’t any continual source of moisture affecting the area, stable, continuous room conditions may help it change on its own. If you find this doesn’t help, you may wish to contact a certified inspector to take a look http://www.nwfa.org.

      Jason

  14. Denise says:

    We installed bamboo floors in our master bedroom. The contractor glued them down according to the specifications. It has been a humid summer and in spit of running a/c the floors are now buckling. We had the contractor come back and he nailed them down in several places. The floor was fixed after the that. We kept ac on and now it’s buckling again. What do we do?

    • Jason Spangler says:

      Denise:

      Thanks for the question and sorry for the problems. Being very simplistic in my explanation, the moisture content of the bamboo has changed since installation. I would recommend you contact http://www.nwfa.org and look for a certified inspector in your area that can help pinpoint the culprit of the problem. Good luck.

  15. Stephanie says:

    I use a shark steam mop on my real hardwood floors. The floors are 23 years old. We live in North Florida – very hot and humid. I’ve noticed very minor cupping over the past year or two. Could it be from my shark steam mop?

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