Okay, the mfg. of my flooring (5" wide, T&G 3/4" nail down oak) states that on 4" and wider boards, the moisture should be no more than 2% different between the flooring and the subfloor. I have 4% or greater. My subfloor is showing about 12% and my flooring is 6-8%. Both have been acclimating for a few weeks. One problem I see is that the HVAC is not running much. I have been there all day long working sometimes and the house will stay a comfortable 68-72 degrees with no HVAC running. My hygrometer is indicating that the house is at about 70% which seems high. I might need to check with a different hygrometer.

Anyway, I would like to start installing the flooring soon but I am concerned about the discrepancies between what the mfg. says and what I have. Any advice?

Thanks,

Jeff

For me, when an interior subfloor reads 12% MC, that starts the red flags waving. That is the max acceptable MC for wood subfloors. But your RH is pretty high as well at 70%. You need to get the RH down by running the AC sometimes. And you should think about taking the flooring out of the cartons and "stickering" it. It's a pain but the flooring will not acclimate well in the cartons. I usually would not recommend stickering flooring but your #'s are so far off. Ideally, the flooring will be closer to 8% MC and the subfloor at 10%. Check for leaks or dampness in the basement/crawlspace.

I had work done in the crawlspace and the people that were under there said the moisture wasn't bad. I also had them lay a moisture barrier when they were completed with the floor leveling work. It has been extremely wet here this fall (Oklahoma) so that could be causing some problems. One thing I haven't checked is the 1x8 subfloor in the areas where I will be putting tile. I have laid 1/2" plywood over the 1x8 subfloor and the plywood is what is reading 12%. I'll check the moisture in the 1x8's tomorrow and let you know what it is reading.

I have not stickered the wood yet. I was planning on it but I need to lay the felt paper out first. I sure don't want to have to move it all once I've stickered it to lay the felt paper.

Thanks,

Jeff

Do NOT lay the felt paper yet!.....it will act as a moisture barrier, holding moisture in the plywood, and keeping it out of the rest of the house, throwing off your readings. Open the wood, get it stickered and let it acclimate properly....there is no set time line, trust your meter and get it within 2%, especially on a wide plank. And get the humidity down....70% is way out of line, especially since you could expect to be between 20-30 this winter. You install the wood now with that RH%, and you're going to have gaps and probably a good deal of cupping when you start running the heat.

I am seriously doubting that the actual humidity is 70% seeing that the outside RH is around 50% right now. My heat has not been running much but it is turned on. I would expect the RH in the house to be somewhere in the same range as the outside. Maybe I am wrong but I can tell you that the hygrometer was reading 70% when it was in my garage as well. So, I will get another one and check the RH in the house again.

I was pretty sure that the felt paper will hold the moisture in the subfloor. That is another reason I have not laid the felt paper yet. Thank you for confirming that.

So you are suggesting that I sticker the wood, then when the moisture levels get right, pick it all up and lay the felt paper? If that's the way it needs to be done, then that is how I will do it.

Thanks,

Jeff

Just went and checked the actual 1x8 subfloor this morning. It is showing 16-18% moisture. So the 12% in the 1/2" plywood underlayment doesn't sound unreasonable.

Jeff

You almost definitely have a moisture problem from under the sub-floor system. Best to get that attended to before even considering your hardwood install. Personally, I would be taking the flooring off-site until you reduce the MC to something more reasonable.

Well, I have done all I know to do about getting water away from the house. I know that water does not stand under the house. The yard is graded to move the water away from the house. Gutters installed, downspouts direct away from the house and will eventually be tied into an underground drain so that they do not dump in the yard. Moisture barrier installed in crawlspace. There are no plumbing leaks. I don't know what else I can do to get rid of the moisture. Does anyone have any more suggestions?

I could possibly install a ducted fan to bring air from under the house out the top. Basically install a duct that runs from floor to roof and install a fan to pull air from under the house, push it through the duct and out a roof vent.

Thanks,

Jeff

Have you completely covered the earth with 6 to 8 mil polyethylene ( plastic sheeting )?

I had my floor leveling company install a moisture barrier (6 mil polyethylene sheet). I am assuming that they completely covered it. I have not been under the house and really have no burning desire to go under the house (claustrophobic). I am trusting that they did their job correctly.

Thanks,

Jeff

Cross- ventilation utilizing the prevailing wind direction will be more efficient than venting upwards through the roof.

Your assuming but wont check? lol Good grief. What if they installed the plastic upside down!!!

Ahhhh, now I have to check and make sure my painter put the finished side out too!

Dennis - all of the vents around the house are opened. Not sure how to add more without a pretty significant cost. North/south winds are prevailing around here and those sides of the house have vents.

Thanks,

Jeff

Check your local building codes, there is a formula for calculating the amount of vent space required based on floor area of the crawl space.
This is a variable depending on local climatic conditions, which is why you should check your local codes.
It may be possible, if the amount you have is inadequate, to install a fan on the north side to increase the flow of air, I don't know, im not an engineer, but this information should be available to you locally.

Thanks Dennis, I will check into that.