The wood floors in my 1926 Craftsman style bungalow started cupping this year. In some places it is subtle, in some places it is really extreme. Ideas on what is causing it and what could fix it?


  • I had the floors refinished last year, by two separate people, and both areas are now cupping.
  • I am in Austin, and it has been a very humid and rainy year, compared to the normally dry climate
  • I have had a high humidity problem in my house. Had an AC installed a year agonizing my attic and it has never cooled or dehumidified properly.

Suggestions I have received:

  • change out all of your ceiling vents (I did It)
  • change them all back
  • get a radiant barrier and insulate the attic
  • insulate the floor - there is no insulation down there.:

I have bought a stand alone dehumidifier which I empty twice a day. I think it's helping

  • 1
    Humidity is definitely the cause of your problem. Some of the cupping may go away if you can lower the humidity level, but if cupped too bad, it may be permanent. Commented Aug 16, 2016 at 11:55

2 Answers 2


Cupping to me means the wood board is curling up on the edges..usually on the long edge of each board. (Concave.) Cupping is caused by moisture, sometimes humidity , but could be by moisture "introduced" into the flooring.

High-humidity or low-humidity usually does not cause rapid cupping, like you're experiencing, because it's introduced slowly and uniformly into the wood. However, if you've experienced an unusually high humidity this year it could add "moisture" to the boards which would expand the boards, thus causing each board to grow and could push against the walls. Usually, this causes the entire wood floor to bow up. If this is not what's happening, and I suspect not, because you described cupping, then it's moisture being added to the floor.

I don't think installing a new HVAC unit will cause cupping. Here, we prefer a system that moves air rather than a "radiant" type heating system because it dries out the air (we have a relative humidity of 80% or more year round...), and we don't have a cupping issue.

A humidifier will dry out the top of a board causing it to shrink, thus shrinking the top more than the bottom...causing cupping.

If the wood floor has been fine for many years and has started cupping recently, then I suspect moisture from leaking plumbing, leaking roof/drain, moisture from crawl space, or even a water event...like a large spilled water container. I know, sounds crazy, but water will drain down between boards and lay on the subfloor, then soak into the back of the wood flooring. It could take months for that to dry out...and the bottom of each board will "grow" while the top of each board will dry out rather quickly. (Do you have kids?)

You must find the cause quickly or face a big expense of replacement or major repair (sanding entire floor.) We discovered a leaking drinking fountain near a high school gym and it caused such a problem that we had them chainsaw the entire floor out and replace it. If you can find it quickly, the boards will not "set" and you can run fans (not humidifier) and allow the boards to lay flat again. Is the entire house's wood floor cupping or is it just occurring in one or two rooms?


I feel as though the floors are now much dryer than when they were sanded and finished a year ago. Even though the AC seems to not work properly, it still removes humidity.

If you can cool your home and keep a decent level of humidity in it, 35% or so, you may find that your floors may flatten out a bit, depending on how much moisture content they had before they were sanded.

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