I recently bought a house with laminate flooring in a partially-below-grade room that sits on a concrete slab. The owners ripped out carpeting in the room and installed the laminate prior to putting the house on the market. The house is ~40 years old, and the owners (who were the original owners) claim that the carpet never appeared to be moist during that time.
Subsequent to our going under contract on the house but prior to settlement, there was a lot of rain and the laminate apparently started bowing. The sellers (without consulting us first) decided that the problem was due to moisture absorbing into the slab, so they replaced the gutter above the room, re-graded the side of the house, installed a French drain, and replaced the bowed floor boards. I have now been living in the house for about a month, during which we've received a lot of rain, but everything seemed to be fine. That is, until a few days ago when we received a downpour of about 2 or 3 inches of rain in the span of about 2 hours. A couple days later I noticed that some of the floor boards had started to bow. It is in a relatively isolated area, approximately in the same place (I am told) where they had previously bowed. Therefore, I am assuming this is not due to expansion gap issues.
We are contacting the contractors who did the work for the previous owners to see if they have a warranty/guarantee, however, in the event that that does not work, what is the next step? Could it be that the French drain and gutter modifications were insufficient? We don't want to replace the floor boards just to have this happen again in another few months…
Best Answer
There are 3 potential moisture issues:
You need to first figure out which of those 3 is happening.
If the water is leaking in, that's an issue of gutters, grading, draining, etc. That needs to be fixed on the outside, first.
If moisture is migrating through the slab, then you may have a high water table. If that's the case, I wouldn't bother finishing the basement. If it's just a bit of moisture, you could get by with putting down plastic underneath the laminate flooring.
If it's high humidity, then this might be the gap issue. Engineered floors shouldn't expand/contract as much as real wood, but they still need plenty of space around the edge of the room to expand. Check for that. Otherwise, get yourself a quality dehumidifier and have it run 24/7.