Minimize Moisture Under Hardwood Floor

Q: I installed a 3/4" tongue and groove hardwood floor in my dining and living rooms. I have been advised to do several different things to minimize moisture from the crawl space that could affect the floor, but am not sure which is right.

Should I install plastic on the joists?

A: I would have started with plastic then a subfloor before applying the hardwood flooring. I don't know if you glued or nailed the floor down.

Fortunately, that flooring is an engineered product, so it will have better control over the expansion and contraction that can occur due to moisture changes than a traditional solid wood floor.

I advise against attaching any moisture barrier directly onto the floor joists because you could trap moisture from the home in your joists and create a problem. At this time, I recommend installing a small fan and perhaps more venting to increase air circulation under the area to keep it dry. Then wait to see how the flooring reacts with your home's humidity before spending more effort or money, because it might be just fine.

John Fuchs, Senior Carpet Inspector and Flooring Consultant, Carpet Warehouse, Rancho Cordova, CA