I have a client who is has a lovely house built in 2010 that has oak hardwood floors throughout. There are apparently no other moisture issues besides the hardwood flooring. This problem is on the third floor and the house has hardwood on all three floors. The owner is noticing that the first floor is starting to have the same problem. Important to note that the third floor warping is directly in the middle of the floor and runs the length of the third floor. The house has an open staircase that goes from the first to the third floor. There has not been any moisture around the windows. The house has warm air heating. The floor(s) have been replaced but they are warping again. Owner is assuming that it is an excessive moisture problem and wants to install dehumidifiers.
I haven't seen the house yet and a blower door test has not been done. I don't want him to spend money on an expensive dehumidification system if it isn't going to cure the problem. Thoughts would be welcome.
David, your suggestion is really very good. Since so many dishwashers are hooked up into the sink, it's obvious to check only the sink. But if the dishwasher motor seals are failing, water will drip out onto the flooring and follow it back to the lowest point. Seldom is the lowest point in a floor near the outside walls. And it may be following the subfloor -- mostly invisible to the owners.
Nine years in the house is about the time you would expect dishwasher seals to fail..
Refrigerator leaks can do the same...
How are your gutters and downspouts and extensions functioning? and is the land still banked away from the house properly? Hundreds of gallons of water come off an average size roof during a say 1" rainfall. Best time to look at this is during a downpour. I had one home that went from needing 2 basement dehumidifiers emptied each day to once every 2 days just by regrading a few spots around the perimeter of the house.
I'm skeptical there is a humidity problem on an upper floor this time of year, but first step would be to gather data. Measure humidity. For $100 or less one can by a USB ported temperature and humidity logger.
Does the home have excessive internal sources of humidity such as 5 big dogs or a gazillion house plants?
This may be too easy of an answer, but I had a problem similar to this in a rental home I was working on. Turns out the occupant was using a steam mop (Shark) and thought nothing of it since she "used it on all her hard floors." This is probably something that is laughably simple compared to what you are facing, but you might want to gingerly ask how the floors are generally cleaned at your clients home.
My observation is this - Mid Atlantic region: If a 2400 ft2 house is at about 5-8 ACH50 (which most new houses here have been at since about 2000) and there are 3-4 people in it, then the RH is about 40-45% if there are no other moisture problems. Enough spaghetti gets cooked, enough showers get taken, and enough breathing is going on to supply a balance with the air leakage to maintain a reasonable RH. If the house gets smaller, tighter, or more heavily occupied, you can get problems. Likewise if a house is bigger, looser, or more lightly occupied you can get problems.
One of the local large (3-400 a year) national builders specializes in houses over about 3500 ft2 and on up to about 6500 ft. They found that if they installed a humidifier on each system as standard (either 2 or 3 systems) their floor warranty problems virtually disappeared.
If this house has 3 living floors, it may be a large house. And the third floor maybe the warmest, therefore have the lowest RH.