Looking for a cure for a warping hardwood floor not caused by a leak

I have a client who is has a lovely house built in 2010 that has oak hardwood floors throughout. There are apparently no other moisture issues besides the hardwood flooring. This problem is on the third floor and the house has hardwood on all three floors. The owner is noticing that the first floor is starting to have the same problem. Important to note that the third floor warping is directly in the middle of the floor and runs the length of the third floor. The house has an open staircase that goes from the first to the third floor. There has not been any moisture around the windows. The house has warm air heating. The floor(s) have been replaced but they are warping again. Owner is assuming that it is an excessive moisture problem and wants to install dehumidifiers.
I haven't seen the house yet and a blower door test has not been done. I don't want him to spend money on an expensive dehumidification system if it isn't going to cure the problem. Thoughts would be welcome.

Tags: humidity, warped floor

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Water leak in nearby bath / Condensation on duct runs / exhaust fan not venting outside / cold water line condensation are all items that could be happening under said floor. Until you are out there it is pretty hard to diagnose. Shoot did they check the moisture content of the subfloor before putting down the new one / let it acclimate

Hi Paul and Sean,
Sean, < Shoot did they check the moisture content of the subfloor before putting down the new one / let it acclimate>
That would be my first guess, although you said they have replaced the floor once. If it was installed by a flooring co, they would certainly know how to acclimate the wood. A GC might rush the process.

As for acclimating the wood, that is still a difficult process in modern built homes. Most flooring companies still expect low RH in the winter, but a tight home may actually be too humid.

Buckling in the center is a clear sign it was installed too tight. I would get the dehumidifiers going asap as once it raises too much, it will not go back down. Good job for an IR camera, looking for a source of moisture, but my bet is no leaks.

Ask who installed it, how they acclimated it and moisture content. If a contractor installed it, find an old floor company and buy him a cup of coffee. We used to leave the bundles on site for at least 6 weeks, before installation. No moisture meters back then.


Before spending the money for humidifiers,  perhaps a good test would be to place some temp & RH data logging equipment in the house.  See what really is happening.   I've been using the logtag data recorders at:


They were designed for tracking environmental conditions in food shipments.  But they work very nicely for other applications.  The software is free and is actually quite amazing.   I stumbled on them while looking for something that would be simple and inexpensive to record conditions in multiple rooms of a house.

If you have a couple of logging  temp/RH evices,  you might set one on the floor, then next to it set another up with a plastic container over it.  See if you can determine where the moisture is coming from.  

If the house is seeing big seasonal swings -- that certainly can cause the problems.  However if the humidity is already low, and you keep trying to dry it out more with more dehumidifiers - that will just result in problems elsewhere.  Plus the extra cost to run humidifiers.

Acclimating wood at the installers warehouse does not work as well as acclimating it in the house (putting the stack in the garage or basement for a week or two --- doesn't work).

They also need to check/verify that ventilation for high moisture areas is working as expected.  A bubbling spa bathtub will add a lot of warm (rising) moist air into the room that doesn't have working or a correct ventilation design.

Paul, you say "warping" but I assume you mean cupping. Which way, up or down? Or, is it shrinking/gapping? What is the width of the flooring? What grain? What climate?

You said it is occurring the full length of the house, now on 2 floors? Was the same flooring company used on the replacement? I also wonder about the acclimation time. What thickness and width of flooring?  

A third floor on a newly built house, so this is not an attic conversion. Does the warping occur on both floors at the same location? Is it near a load bearing wall? If so, how does the load transfer to the foundation?

I would sign them up for a complete audit, and run all tests, take pics and go from there.

Hello Paul -- you have generated a lot of thought and commentary with this post. You won't find a more enthusiastic crowd than a bunch of building scientists trying to solve another building scientist's quandaries. I've seen the problem you describe in more cases than I want to admit, having installed about a quarter-million square feet of flooring in the 70s and 80s.

My analysis. I suspect that the warping you describe runs the length of the floor, along the axis of the flooring, and is characterized by buckling rather than cupping alone. If so, it's a function of room-wide expansion, rather than a point-source moisture problem. I'm pretty sure this would be caused by either 1) installing the floor without letting it acclimate for several weeks inside the house (amply pointed out by others in this discussion), or 2) by not leaving a reveal at the edges against the walls (more important than many installers realize.)

In the absence of these installation errors, an excessive amount of moisture could cause this type of buckling. But if the home were that wet, I'm sure you would have long ago identified the moisture problem.

Crazy story that illustrates this principle. We once repaired a situation like this by removing one 2 1/4" board from the middle of the floor, making a set of skil-saw drop-cuts to remove it and relieve the pressure. This worked like a charm, with the flooring laying down over a period of a few days under the weight of some timbers and sandbags. We milled a slip-jointed strip to replace the removed board, and when I last saw it that floor was still flat after 10 years. I'm not saying that this is an approach that you'd want to experiment with in a client's home, but it does show you how buckling pressure is ultimately created at the floor/wall intersection.

One wrinkle to consider. If you install flooring during dry winter conditions in a climate that experiences wet summers, your flooring could be TOO dry when it goes down. If this is the case, you'll have to leave gaps out in the field to accomodate the eventual expansion. I've often gapped flooring using a set of .025 feeler gauges to space each course. Sounds crazy but it works well and the gaps aren't very noticeable. Any experienced flooring contractor will use a moisture meter to evaluate the stock before they install it -- 4-8% is the typically acceptable range. And they'll know how wet the flooring will get in during the wet season in their climate -- 8-10% is possible in some climates, and in these regions some controlled gaps may be needed.

Your flooring contractor considered all this, right?

Everything does affect everthing else! Sometimes one particular thing could be the culprit. But then again, this culprit has a whole series of it's own elements. Thanks for this insight Chris. Great stuff.


Thank you for all the input.  One of the things I love most about this community is that so many people are willing to bring their knowledge and experience to bear.  I have set up a time to check the house out next week.  I will bring my gadgets including my Hobo dataloggers and we'll see what we can see.  I'll let you know.

Let me know if you'd like a second set of eyes

Great to see all the responses because I too have a severe warping problem on my kitchen hardwood floor. Floor was installed by previous owner in 2001 - he installed it wrong directly over plywood sub-floor without resin paper and left no gaps for expansion. I moved in In 2003 - from 2003-2009 no warping at all.  Then 2010-2012 every summer severe warping - floor bends 5-6" upward in a 3'x6' rectangle in front of kitchen sink and dishwasher.  Me, my IR camera, and a plumber have checked for all possible leaks and replaced most of the supply and waste pipes - no actual plumbing leaks ever found. Didn't solve the warping.

Floor is above a 4' crawlspace thats poured concrete - foundation built in 1972. No visible signs of pudddling but poured concrete is poured over boulders.

I suspect it's extreme humidity in crawlspace below thats causing the warping in the floorboards above.  

I just can't figure why its only in this on 3x6 area and not in the other 400 sqft. of same hardwood floor thats over the same crawl ?

And I cant figure why there was no warping the first 6 years in the house - nothings changed in the crawlspace ever ?

The floorboards always go back down to normal flat every winter.

This summer I'm gonna leave an RH datalogger in crawl to see if a dehumidifier is warranted. 

PS - House is tight - blower door leakage is only 15% above BAS. 

Any ideas would be appreciated... 

I think you need a pinless moisture meter. Go over the entire floor and see if there is a damp area concentrated in front of the sink/dishwasher. Check the subfloor from below as well. You might have a small plumbing leak from that's getting under the floor. In the winter, conditions are such that it dries out. In summer, it doesn't. Just a guess, but proximity to sink/dishwasher sounds like more than a coincidence. Is there a forced air outlet in the toekick under the sink?


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