Humidity and wood floors

Q: I recently moved into a newly built log home in Northeast Ohio. I have hickory floors. The floors were put down in the dead of winter (January) and the humidity in my house was very low. By May I was having a problem with the floor, wavy in some areas and actually buckling in one room. For the last two weeks I have been running dehumidifiers, ceiling fans, and the air conditioner to try and bring the humidity down, but it almost seems like the waviness is getting worse not better.

I understand that the humidity should stay as constant as possible, summer and winter, but what is the ideal humidity for wood floors? The man who installed my floor is telling me 30%, but it seems like I can’t get it there. Any clues on what I could do?

A: I have to assume that this cabin is heated in winter. Humidity is a tricky question and the figures that some companies recommend seem unrealistic outside a laboratory. For example, I have read to keep the RH in the home between 45-50% year round. We could not allow that in our climate! In the winter, we would have streams of water running down the windows and walls. I heat with forced air and in winter it is typically RH 33-40 in my house. I don’t want it dropping any lower or going any higher. I think your installers number of RH 30 is unrealistic for our climate, especially in summer. You couldn’t keep it that low.

I think this is the best work around. When installing in winter with heating in place and typically low RH in the home, a humidifier should be running at that time of year to raise the RH to at least 40%. Like I said, you can’t go much higher without creating condensation issues. But, at least you won’t be under 30% and then face a huge swing when spring comes. If a humidifier had raised the RH in winter when the floor was installed, then you should be able to keep it down to 50-55% in summer. I have one of these digital dehumidifier’s running in my basement and I can set it to any figure I like. It can handle 3000 sq. ft. and does a good job. So, if the floor was installed at about 40% RH in winter and now in summer it rises to 50-55, that is only 10-15% difference and shouldn’t cause a problem.

Here is another factor that can come into play when installing at low RH in winter: You take the wood into the house and let it acclimate. It is dry in the home so the wood shrinks a bit. The wider the board, the greater the expansion and contraction. The floor is installed and nailed nice and tight. You have to know that in summer when the RH increases 30-40% or more, the floor is going to expand. It is absolutely imperative that an expansion gap be left around the perimeter to facilitate the expansion. If the floor is installed tight to the walls in winter, when it expands, something has to give. I would check the floor along the walls. If it is tight, you may have to remove that row of boards or find a way to cut it back to allow an expansion space.

I hope some of this is helpful. Hopefully this floor can be gotten under control and it will settle back down without any repercussions.