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The Problem
I was asked to look at a floor that had severely cupped "for no reason." It had been in place for only a few months. The homeowner was a "wood person," and he explained to me that there was noway the floor could have cupped the way it had, as it was a lake house, the home had not been used that frequently and they kept the inside temperature at a constant 78 degrees Fahrenheit when the house was not in use.
The Procedure
The floor was 3/4-inch-thick, 5-inch-wide solid white oak laid on-grade. The home was a split level house with a crawlspace that was adequately covered with 6-mil poly. The subfloor was over suspended joists that were either open to the crawlspace or had been insulated and sheet rocked. The proper nailing schedule was followed. The home seemed to be at a comfortable living temperature for March and did not have any evidence of mold or mildew from heavy, damp, humid air.
The Cause
I began my inspection on the lower level of the house. The lower level was a basement/split level. In areas where the wood flooring was installed, the grade of the land was at least on ground level. There was not any evidence of water below, and the hygrometer read roughly 67 percent. Considering this was somewhat high, I first suspected that the floor was wet and that the subfloor and joists must be wet.
Using a probe moisture meter, I checked the joists and subfloor for excessive moisture. Once satisfied that they were within normal ranges, I immediately went back up to the top floor to check the wood floor itself. It also was within the acceptable range. There was only a 3 to 4 percent difference in the moisture content of the wood floor and the subfloor. The moisture content of the joists was not much higher.
Knowing that the only thing that could have caused this floor to cup was moisture, I turned my attention to a crawlspace that was adjacent to the top floor. The layout of the floor plan allowed for a partial crawlspace and a partial finished living space below. I began to measure the amount of cupping in boards from room to room. I noticed that the boards in the area over the crawl spacewere slightly more cupped than the ones over the living space. Opening the crawlspace, I found it was adequately covered with 6-mil poly, but the air was extremely damp. Placing the hygrometer in the crawlspace and allowing it to sit for the necessary time, I found the overall relative humidity in the crawlspace was in excess of 75 percent. Then, I turned over some of the poly, revealing a severely dampened condition. The homeowner,the distributor and the installer insisted that they had not had rain in the area for at least three to four weeks. I looked further into the crawlspace and noticed that although it was a relatively windy day, there was no air movement.
I asked how long it had been since the homeowners had used the house, to which came a suspicious reply of three months. I asked if there was no heat turned on during those three months, and the answer was somewhat shocking: The homeowners did keep the home at a constant 72 to 78 degrees when in use, but the remainder of the time it was turned way down or up depending on the season,and everything was closed up.
How to Fix the Floor
The floor had cupped during the time the home was not in use and there was no air flow through the house. I suggested that they always keep the house at a constant temperature range and that crawlspace fans be installed to adequately move air under the house. Once fans were installed and the HVAC was set constantly, the cupping was reduced, although the floor did need to be sanded and refinished. Since then, there have been no problems.
In the Future
It is best to consider all of the job-site conditions when making a product recommendation, even though the product may not be exactly what the homeowners think they want. In this case, the installer should have asked specific questions regarding the use of the house. It would have been a better option to install a wide-width sawn engineered board, which could have withstood the slight amount of increased moisture that cupped the 5-inch solid board. If he discovered that solid wood was the only acceptable option for the homeowners, then he should have taken extra precautions to make sure they were educated about maintaining the right temperature, humidity and air flow through the house and crawlspace. Oftentimes, knowing the right uses can save you some abuses.