"Marsha" wrote in message

We have an addition on a crawl space. The crawl space is about 3'
high. Underneath on the ground is rock dust with plastic sheeting over
top. The spaces between the joists are insulated.

We had hardwood flooring put in the addition. Within about 6months the
planks are cupping. It's very slight but it is noticable (at least to
me). What is causing this?

Floors/boards cup for one reason, a differential in moisture content on
opposite sides.

The drier side will be the concave, the wetter, convex.

What you are seeing is the results of this simple fact, but mitigating it
may not be that simple, and much depends upon your climate.

The obvious solution is to insure that both sides are subject to the same
relative moisture/humidity levels and you need to think along that line for
finding a solution.

Something as simple as moving air in the crawlspace (fan ventilation) may
help, or you may need to humidify/dehumidify one side or the other, or both.

... or you may need to learn to live with it on a seasonal basis. Some of
the finest OLD houses in the world exhibit this behavior at certain times of
the year, particularly in areas where/when there is a marked change in the
seasons.

Good luck.

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Last update: 10/22/06