Hardwood too tight

Originally Posted By: jnosworthy
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Instead of the more frequent installation problem of “cupping”, what we have here is “crowning”. An entire house worth. The home is new and occupied about 9 months now, single story over crawlspace. We have entered the second heating season on this floor, and some slight gappage would be expected right about now. Instead we have a very “pinched” appearance as though there is too much moisture present and the floor has no where to go but “up” in a hump. The homeowners contend that the problem was not there when they moved in last Feb., and has become more evident over time. They want the builder to “fix” the problem.

My investigation tells me the site and all nearby houses in this same new development are probably experienceing drainage problems associated with a layer of clay near the surface. We are fairly certain that the crawl was probably very damp and the vapor barrier may not have been in position before the flooring installation started. (Installer’s responsibility not to start the job, if so, I told. But builder’s responsibility to actually install the vapor barrier).

My moisture readings now indicate crawlspace framing at 13% to 15% and slightly less for the underside of the subflooring. The dirt under the plastic is saturated. The hardwood is consistently at 8% throughout the living level, as is the subfloor when measured from inside the floor registers. The “crowning” amounts to about 1/32 (a dime coin) at each and every board. RH inside the dwelling was at 57% and 67% in the crawl, the day I tested. The homeowner has already disconnected the humidification equip added to his furnace. And finally, this was a Pre-finished hardwood product.

We can toss out the two most frequent causes of “crowning”. The first is associated with sanding floors at the wrong time, while cupped, and then they dry out and lay down and then you discover the opposite problem. Forget that, this is new pre-finished. The second “explanation” is too much water added on the top surface side. I really don’t think the homeowners wet mop their hardwood floors ! They are “swifter” type people. Just two retired folks who each work part time out of the home, with normal amounts of vapor causing activites in the house. All the usual suspect moisture capturing devices are vented to the outdoors.

And finally the last explanation I could find, which is the one I’m going to hang my reputation on. I want to believe that the unfinished underside of the flooring has actually given up excess moisture back through the 15# felt vapor retarder, in the direction of the crawlspace. The vapor pressure is now reversed, causing the bottom of the strips to shrink, and thus the finished top surface is wider, hence the “crown”.

Am I missing anything? Any other thoughts out there ?

Originally Posted By: dvalley
This post was automatically imported from our archived forum.


Crowning is either caused from moisture intrusion or from sanding too early after it has already cupped.

Here's a great site that'll explain it better than I can...

David Valley
MAB Member

Massachusetts Certified Home Inspections

"Some cause happiness wherever they go; others, whenever they go."

Originally Posted By: dedwards
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Another possible explanation is the wood was not allowed to acclimate prior to installation. I have laid different types of floors from hardwood, laminates, etc. and they all have one thing in common. The wood is supposed to be removed from the cartons and allowed to acclimate 48 hours prior to being nailed down. I do not know how many times I have seen what you are talking about and almost every time the homeowners said the installers took the materials out of the cartons and installed it in one day. Moisture is the problem for sure but when and where it became the problem is the question. Hope that helps

Originally Posted By: lewens
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Another problem might be the floor itself. Is the product supposed to be nailed down or is it supposed to float. If it has a snap lock system in the t and g it is most likely meant to float and nailing it will not allow that to happen, hence the crowning. It could also be too close to the edges thus not allowing it to expand. It should be given enough room to expand and contract. Wood breathes.