Question for this board. Although it is not best practices, it is related to retrofits?

I walked into the house today and the entire ~1300+ sq.ft. of the hardwoods were rippling/cupping at the joints (there was also carpet and tile, but no visible problems). I took a moisture reading of the poly coated walnut and it was 8.5% from inside the house. I took a reading of the yellow pine joists under the house and they were 9.5% (but exposed to earth). I chiseled out some of the closed cell and the reading on the subfloor was 16%!! !

It was retrofitted last year with foam - closed in the crawl, open cell in the attic. The crawl was sprayed first. They were replacing the hardwoods in the house at the time due to aesthetics, not an existing problem. The hardwoods were delivered in February of this year, 2010, after being shipped on a boat in a container. They were left inside the house to acclimate for a week or more before installed, but were brought in during a rain. There is some debate as to whether Heating was on the entire week prior to the install or not and when they actually got installed due to the foam being installed in the attic and the hoses running inside the house. There is no record of how dry they were at the time of install, nor the moisture content of the subfloor. The problem didn't show up until June this year!

Is there any way that moisture drove through the felt into the subfloor and is trapped there due to the foam? Obviously it is trying to escape as there is cupping going on, but any suggestions or ideas? Has anyone seen this problem before? There are no apparent water leaks. The foam job looks good, although an average thickness of maybe 1.5" (some thick spots and some very thin). The attic foam job was good, but did have some bypasses that need to be fixed.

The owner of the house is a HVAC and Building Engineer and even had a thermal camera. He seemed sensitive to the fact of me asking about his RH in the house, but stated it was well maintained. There is no visible signs of microbial growth and he said he keeps the house at 73 degrees all year around!

Any ideas?  Thanks!

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Replies to This Discussion

Forgive me for not having all the numbers handy but 16% is not conducive for mold to grow as I recall

The problem started in June because the AC kicked on allowing for the top of the wood to dry before the bottom which results in the cupping of the wood. It sounds like the problem is not caused by the CC foam (which does block moisture transfer) but the original conditions the floor was installed. I have a sneaky suspicion that the wood was not properly acclimatized and the moisture levels were not checked. Add into this the spraying of OC foam in the area (Let me guess with water as the blowing agent) just exacerbated the situation by adding more moisture into the air & materials. To further make matters worse, I can bet the "well maintained" RH levels are a function of a humidifier used during the winter months.

As for the "driven" question - nope, think about the laws of physics - hot to cold - wet to dry unless something is forcing it to go another direction, then ask yourself which way the water / moisture would be moving --- while he can see if the floor returns to normal over the winter, I would suggest he waits till the AC is back on before getting the floor redone if it doesn't  return to normal. This time when they acclimate the wood, it needs to be done with the containers opened and the subfloor needs to be around the 7 or 8% mark as I recall if not drier. Also depending on the product, you are talking about anywhere from 3 days to 3 weeks for proper acclimation to occur. (longer period for solid wood)


Hardwoods do not cup because moisture was driven out of the hardwood through the felt and is trapped there.


Wood changes it's shape in reaction to moisture changes or the release of tension.  Generally the moisture changes are a drying out, where the moisture in the wood, leaves.  Like heat, moisture leaves the easiest way possible and always moves to areas of less moisture.

I work with wood as a wood turner. Starting with a fresh cut log and roughing out a bowl to allow it to dry and warp. Then being able to finish turn it to a final object.

The wood was imported from overseas, it came over on a boat. The were placed in the house in February, allowed to acclimate. Then installed.  In June they began to cup.  What would the RH in the house have been in Feb.? How about the outside climate?  What is the RH in the house in June?  How about the climate?

I think everyone is assuming the moisture is from the newly installed flooring.  I am not so sure.  Where else could it have come from?  If the wood was installed wet, 12 - 20 %  then it would have dried to the room, not the sub floor. (At least after the subfloor and the floor reached the same moisture level.)  The subfloor does not have 2x moisture compared to the floor with the excess coming from the floor.  The floor did not cup to allow the release of moisture from the subfloor.  The floor cupped because of a change in the level of moisture within it - or a change in tension.  Was any of the wood milled onsite?  Was a lot of it cut to fit onsite?


@Jamie - "Is there any way that moisture drove through the felt into the subfloor and is trapped there due to the foam?"


Are you saying there is felt paper ("tar" paper) under the flooring? So from the bottom up it goes like this: CC Foam, Plywood (or OSB) Subfloor; Felt Paper, 3/4" Solid Walnut flooring (not 'engineered' walnut veneer)?

If I have that right, the one thing that jumps out at me in your data is the large differential in moisture content between the subfloor and both the floor joists and the flooring (twice as much).

Essentially there is a "sandwich" of moisture barriers around a hydrophilic subfloor. I can imagine that that could create a problem, particularly if, as @Sean suggests, the OC foam was applied with H2O as the blowing agent and the subfloor was not allowed to dry out sufficiently prior to flooring going down.

I suggest this: The moisture differential between the subfloor and the flooring is your culprit. The moisture isn’t being driven through the felt paper, but already existed and is being trapped by it. Although felt paper is a "moisture barrier," unless the seams are taped and there are no staple holes, tears, etc. then moisture will still move from high to low – back into the bottom of the flooring. Walnut, although considered a 'hardwood' is not much harder than SYP (Janks Hardness Rating). And is likely to dry out faster on top and cause cupping.

The CC Foam is doing its job preventing moisture from escaping the subfloor into the crawl space… and so is the felt paper - just not quite as well, but enough to keep the subfloor more moist than the flooring.

I've installed many hardwood floors in upstate NY, and I always use a heavy builders paper or Kraft paper underneath the flooring, above the subfloor, to reduce friction related noises while still allowing moisture to move through the system (that is: assuming you are not over a uninsulated crawl space or other area that isn’t conditioned and/or doesn’t already have a moisture retarder - there’s almost never just ONE easy answer :-)).

Another remote possibility is this: The flooring was installed too tight against the walls with no room for natural movement... this would probably result in a more violent, less uniform upheaval (not cupping). This seems much less likely, but still worth a look.

I agree with @Sean - let the flooring go through another AC cycle and see what happens. If the decision to reinstall is made, I would suggest leaving out the felt paper in favor of builders paper.

Well described.  I have to think if the crawlspace foam is only 1.5" it was intended as a vapor barrier rather than insulation. In June isn't it humid there?  You said the joists were exposed to earth, which suggests the crawlspace isn't encapsulated or insulted.  Are the joists exposed to this condition or do they also have 1.5" of foam?  If not, maybe the dryer indoors is pulling moisture through them into the conditioned space, wicking through the subfloor, and causing the cupping.


By the way, I think this is a perfect "best practices" question, at least when we look at the house as a system.


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